Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Just to give back to the group, here are the connectors I chose from Digikey to make the GPS MMCX antenna included with the kit detachable for an enclosure: 1x ACX1499-ND CONN ADAPT JACK-JACK MMCX 50 OHM 1x 744-1715-ND RF CABL MMCX ML STR / ML RA 6" Cheers, Joel W0KGW On Tue, Nov 25, 2014 at 1:48 PM, S. Jackson via time-nuts < time-nuts@febo.com> wrote: > That's why I said its up to the user to decide what they want their > trade-off to be. > > For permanent installations I personally would not run the unbuffered 10MHz > output through more than about a foot of coax cable to the buffer. > > The rise/fall time of the TCXO output is slow enough (typical spec is 4ns) > to make that a lumped system rather than a reflected system. You won't see > any reflections on a foot or less of cable. > > For short-term phase noise measurements I have run that signal through 6 > feet of coax no problem, but there are quite significant reflections at > that > point so I would strongly advise against that. If I break the TCXO here on > my bench due to my own stupidity its a different situation than if the > customer has that happen in their setting.. > > bye, > Said > > > In a message dated 11/25/2014 09:34:11 Pacific Standard Time, > csteinm...@yandex.com writes: > > Said wrote: > > >The increased current for the driver will cause heating near the > >crystal in both the CMOS driver and the 3.0V LDO as the LDO has to > >convert the excess voltage into heat. This may or may not affect the > crystal. > > There would be next to no additional heating in the CMOS driver, > because there is very little voltage across it in either logic > state. And the additional power supply current is so small that the > increase in LDO dissipation will also be very low. At the extreme > worst, any such effects would be somewhere between imperceptible and > negligible. But on the other hand, if there is a possibility that a > passive filter can create a clean, 50 ohm sine wave output for free, > the potential up side is huge. > > >Adding an external buffer is so simple that I just did not think it > >would be worth it.. > > An external buffer is a fine way to go, but it would need to be very > close to the driver chip -- which is why I suggested on Sunday > building it onto a breakout card that plugs directly onto the LTE > Lite's MMCX output connector. You really don't want to run a naked > CMOS output at 10MHz much farther than that, both for the corruption > it may suffer and also for the mischief that radiation and capacitive > coupling can cause to other nearby circuitry (the LTE Lite) as the > loop gets larger than that. > > I'm not sure I see why a small additional source of heat is such a > dramatic concern with the 10MHz TCXO, but apparently not for the > 20MHz TCXO, which by accounts has an actual buffer amp that must > create comparatively massive heating. A temperature difference isn't > a problem in and of itself -- only a changing temperature creates a > problem. Whatever the dissipation situation is, it should settle > into stasis if one takes the slightest care with the thermal design. > > Best regards, > > Charles > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
That's why I said its up to the user to decide what they want their trade-off to be. For permanent installations I personally would not run the unbuffered 10MHz output through more than about a foot of coax cable to the buffer. The rise/fall time of the TCXO output is slow enough (typical spec is 4ns) to make that a lumped system rather than a reflected system. You won't see any reflections on a foot or less of cable. For short-term phase noise measurements I have run that signal through 6 feet of coax no problem, but there are quite significant reflections at that point so I would strongly advise against that. If I break the TCXO here on my bench due to my own stupidity its a different situation than if the customer has that happen in their setting.. bye, Said In a message dated 11/25/2014 09:34:11 Pacific Standard Time, csteinm...@yandex.com writes: Said wrote: >The increased current for the driver will cause heating near the >crystal in both the CMOS driver and the 3.0V LDO as the LDO has to >convert the excess voltage into heat. This may or may not affect the crystal. There would be next to no additional heating in the CMOS driver, because there is very little voltage across it in either logic state. And the additional power supply current is so small that the increase in LDO dissipation will also be very low. At the extreme worst, any such effects would be somewhere between imperceptible and negligible. But on the other hand, if there is a possibility that a passive filter can create a clean, 50 ohm sine wave output for free, the potential up side is huge. >Adding an external buffer is so simple that I just did not think it >would be worth it.. An external buffer is a fine way to go, but it would need to be very close to the driver chip -- which is why I suggested on Sunday building it onto a breakout card that plugs directly onto the LTE Lite's MMCX output connector. You really don't want to run a naked CMOS output at 10MHz much farther than that, both for the corruption it may suffer and also for the mischief that radiation and capacitive coupling can cause to other nearby circuitry (the LTE Lite) as the loop gets larger than that. I'm not sure I see why a small additional source of heat is such a dramatic concern with the 10MHz TCXO, but apparently not for the 20MHz TCXO, which by accounts has an actual buffer amp that must create comparatively massive heating. A temperature difference isn't a problem in and of itself -- only a changing temperature creates a problem. Whatever the dissipation situation is, it should settle into stasis if one takes the slightest care with the thermal design. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Said wrote: The increased current for the driver will cause heating near the crystal in both the CMOS driver and the 3.0V LDO as the LDO has to convert the excess voltage into heat. This may or may not affect the crystal. There would be next to no additional heating in the CMOS driver, because there is very little voltage across it in either logic state. And the additional power supply current is so small that the increase in LDO dissipation will also be very low. At the extreme worst, any such effects would be somewhere between imperceptible and negligible. But on the other hand, if there is a possibility that a passive filter can create a clean, 50 ohm sine wave output for free, the potential up side is huge. Adding an external buffer is so simple that I just did not think it would be worth it.. An external buffer is a fine way to go, but it would need to be very close to the driver chip -- which is why I suggested on Sunday building it onto a breakout card that plugs directly onto the LTE Lite's MMCX output connector. You really don't want to run a naked CMOS output at 10MHz much farther than that, both for the corruption it may suffer and also for the mischief that radiation and capacitive coupling can cause to other nearby circuitry (the LTE Lite) as the loop gets larger than that. I'm not sure I see why a small additional source of heat is such a dramatic concern with the 10MHz TCXO, but apparently not for the 20MHz TCXO, which by accounts has an actual buffer amp that must create comparatively massive heating. A temperature difference isn't a problem in and of itself -- only a changing temperature creates a problem. Whatever the dissipation situation is, it should settle into stasis if one takes the slightest care with the thermal design. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Dave, Exactly. Sent From iPhone > On Nov 25, 2014, at 7:34, Dave Martindale wrote: > > The 20 MHz output should be OK, since it is series-terminated with 50 ohms > at the source and the buffer can source enough current. The driver sees a > 100 ohm load (50 ohm resistor in series with 50 ohm coax impedance) for > that 32 ns round trip time, so it will increase power dissipation (as you > note). But the load at the far end of the coax should see a clean edge, > and the reflection should be absorbed when it returns to the source (due to > the source terminator). Just don't look at the signal half way along the > coax. > > The other outputs apparently don't have either the current drive or the > source terminator, so a long piece of coax is likely to do unpleasant > things to the edge. > > In either case, if you want to run any of the signals 10 feet it's likely > better to run a very short connection from the LTE-Lite to a proper 50 ohm > line driver. That gets the power dissipation off the board, and then you > can use drivers that give you whatever output swing you want, and which can > drive a 100 ohm load continuously so you can use parallel termination at > the far end. > > - Dave > > On Tue, Nov 25, 2014 at 12:23 AM, Hal Murray > wrote: > >> >> Said Jackson said: >>> Correct, and thats why its all a bad trade off if you have to use 50 Ohms >>> termination. Either more heat or more PN, and more circuitry. >> >>> So driving 50 Ohms inputs is not optimal here, 1M inputs are much better >> for >>> this purpose. >> >> That only works if you have a (very) short connection to the next stage. >> >> Things get interesting if you have, say, 10 feet of unterminated coax. >> >> 10 MHz is 100 ns, or 50 ns between transitions. Coax is ballpark of 5/8 c >> so >> that's 16 ns one way or 32 ns round drip. That's 60% of the heat as well >> as >> lots of nasty reflections. >> >> (Somebody please check my numbers.) >> >> >> -- >> These are my opinions. I hate spam. >> >> >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Charles, The increased current for the driver will cause heating near the crystal in both the CMOS driver and the 3.0V LDO as the LDO has to convert the excess voltage into heat. This may or may not affect the crystal. One could certainly try, this is why I initially said its certainly possible, but up to the individual to decide. Adding an external buffer is so simple that I just did not think it would be worth it.. Bye, Said Sent From iPhone > On Nov 25, 2014, at 4:12, Charles Steinmetz wrote: > > Hal wrote: > >> > So driving 50 Ohms inputs is not optimal here, 1M inputs are much better >> > for >> > this purpose. >> >> That only works if you have a (very) short connection to the next stage. >> Things get interesting if you have, say, 10 feet of unterminated coax. > > Thinking that the output was a sine wave, I previously suggested testing to > determine what its actual impedance is and to proceed accordingly. Said > pointed out that it is not a sine output, but rather 3v CMOS. Still, I think > it is worthwhile to test to see what the actual output capability is. For > example, most HC and AC CMOS outputs will source and sink 20-25mA. The > Fairchild "advanced CMOS family characteristics" document says: > >> All SSI and MSI devices (AC, ACT, ACQ or ACTQ) are >> guaranteed to source and sink 24 mA. 74AC/ACTxxx >> devices are capable of driving 50 [ohm] transmission lines. > > Some of the newer CMOS logic is similar, including Fairchild TinyLogic UHS > (NC7xZ series), LCX, and LVC devices. Now AFAIK, we do not know what CMOS > device is used for the TCXO output -- and it may well not be any of these. > Testing will provide a definitive answer, and it may show that there are > better options than a 1M termination. > > Of course, the TCXO output is used internally to the LTE Lite (and may be > used internally to the TCXO itself), so one cannot count on having all of the > rated device output current available to drive an external load. Avoid > anything that pulls the output logic levels very far down (logic high) or up > (logic low), say by more than 200mV (such as a termination resistance that is > too low), or materially distorts the output wave shape (such as a Tee or Pi > filter, which one might consider to convert the output to a sine wave and > match it to coax). > > To test, one would use a voltage divider from the logic supply voltage to > ground, with the TCXO output feeding the center point of the divider. (See > attached diagram.) I will be very surprised if it will not drive 10k + 10k > with ease (already MUCH better than 1M), and 1k + 1k is a distinct > possibility [NOTE: in some cases, this scheme works best if the resistor to > the positive supply is about 50% higher than the one to ground, for example > 1.5k + 1k]. You may even find that it will drive 100 + 100 (or 150 + 100) > without problems, in which case it should directly drive 50 ohm coax. With > any of these, best performance in the final installation will be achieved > with the termination resistors at the far end of any wire, PC trace, or > transmission line longer than a few inches. [Note that the divider scheme is > the right way to terminate CMOS logic for analog uses at any impedance -- to > terminate in 1M ohm, one would use 2M + 2M, although at that level it matters > less.] > > Because the CMOS device is a saturated switch, the TCXO and LTE Light power > dissipation will not increase by a significant amount with the increased load > current. The logic supply will need to source some extra power, but only > 45mW even for the 100 + 100 ohm output network. > > If the gods are truly with us, we may even find that the TCXO output will > source and sink sufficient current to drive a Tee network if the circuit is > designed properly -- say, a divider with 150 + 150 ohm resistors (or 220 + > 150) feeding a series 10nF capacitor and 200 ohm resistor to a Tee network > using 10uH/50.5pF/10uH -- which would drive a 0dBm sine wave into terminated > 50 ohm coax with harmonics below -40dBc. (See attached diagram.) This > requires peak currents from the CMOS output of +/- 5mA. But don't count on > this until you test and verify, and don't be surprised if the TCXO output > will not support it. [If one can live with a sine output of < 0dBm, the > divider resistors and the series resistor can all be increased in value until > it does work.] > > Best regards, > > Charles > "All electronics is analog." > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
The 20 MHz output should be OK, since it is series-terminated with 50 ohms at the source and the buffer can source enough current. The driver sees a 100 ohm load (50 ohm resistor in series with 50 ohm coax impedance) for that 32 ns round trip time, so it will increase power dissipation (as you note). But the load at the far end of the coax should see a clean edge, and the reflection should be absorbed when it returns to the source (due to the source terminator). Just don't look at the signal half way along the coax. The other outputs apparently don't have either the current drive or the source terminator, so a long piece of coax is likely to do unpleasant things to the edge. In either case, if you want to run any of the signals 10 feet it's likely better to run a very short connection from the LTE-Lite to a proper 50 ohm line driver. That gets the power dissipation off the board, and then you can use drivers that give you whatever output swing you want, and which can drive a 100 ohm load continuously so you can use parallel termination at the far end. - Dave On Tue, Nov 25, 2014 at 12:23 AM, Hal Murray wrote: > > Said Jackson said: > > Correct, and thats why its all a bad trade off if you have to use 50 Ohms > > termination. Either more heat or more PN, and more circuitry. > > > So driving 50 Ohms inputs is not optimal here, 1M inputs are much better > for > > this purpose. > > That only works if you have a (very) short connection to the next stage. > > Things get interesting if you have, say, 10 feet of unterminated coax. > > 10 MHz is 100 ns, or 50 ns between transitions. Coax is ballpark of 5/8 c > so > that's 16 ns one way or 32 ns round drip. That's 60% of the heat as well > as > lots of nasty reflections. > > (Somebody please check my numbers.) > > > -- > These are my opinions. I hate spam. > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Hal wrote: > So driving 50 Ohms inputs is not optimal here, 1M inputs are much better for > this purpose. That only works if you have a (very) short connection to the next stage. Things get interesting if you have, say, 10 feet of unterminated coax. Thinking that the output was a sine wave, I previously suggested testing to determine what its actual impedance is and to proceed accordingly. Said pointed out that it is not a sine output, but rather 3v CMOS. Still, I think it is worthwhile to test to see what the actual output capability is. For example, most HC and AC CMOS outputs will source and sink 20-25mA. The Fairchild "advanced CMOS family characteristics" document says: All SSI and MSI devices (AC, ACT, ACQ or ACTQ) are guaranteed to source and sink 24 mA. 74AC/ACTxxx devices are capable of driving 50 [ohm] transmission lines. Some of the newer CMOS logic is similar, including Fairchild TinyLogic UHS (NC7xZ series), LCX, and LVC devices. Now AFAIK, we do not know what CMOS device is used for the TCXO output -- and it may well not be any of these. Testing will provide a definitive answer, and it may show that there are better options than a 1M termination. Of course, the TCXO output is used internally to the LTE Lite (and may be used internally to the TCXO itself), so one cannot count on having all of the rated device output current available to drive an external load. Avoid anything that pulls the output logic levels very far down (logic high) or up (logic low), say by more than 200mV (such as a termination resistance that is too low), or materially distorts the output wave shape (such as a Tee or Pi filter, which one might consider to convert the output to a sine wave and match it to coax). To test, one would use a voltage divider from the logic supply voltage to ground, with the TCXO output feeding the center point of the divider. (See attached diagram.) I will be very surprised if it will not drive 10k + 10k with ease (already MUCH better than 1M), and 1k + 1k is a distinct possibility [NOTE: in some cases, this scheme works best if the resistor to the positive supply is about 50% higher than the one to ground, for example 1.5k + 1k]. You may even find that it will drive 100 + 100 (or 150 + 100) without problems, in which case it should directly drive 50 ohm coax. With any of these, best performance in the final installation will be achieved with the termination resistors at the far end of any wire, PC trace, or transmission line longer than a few inches. [Note that the divider scheme is the right way to terminate CMOS logic for analog uses at any impedance -- to terminate in 1M ohm, one would use 2M + 2M, although at that level it matters less.] Because the CMOS device is a saturated switch, the TCXO and LTE Light power dissipation will not increase by a significant amount with the increased load current. The logic supply will need to source some extra power, but only 45mW even for the 100 + 100 ohm output network. If the gods are truly with us, we may even find that the TCXO output will source and sink sufficient current to drive a Tee network if the circuit is designed properly -- say, a divider with 150 + 150 ohm resistors (or 220 + 150) feeding a series 10nF capacitor and 200 ohm resistor to a Tee network using 10uH/50.5pF/10uH -- which would drive a 0dBm sine wave into terminated 50 ohm coax with harmonics below -40dBc. (See attached diagram.) This requires peak currents from the CMOS output of +/- 5mA. But don't count on this until you test and verify, and don't be surprised if the TCXO output will not support it. [If one can live with a sine output of < 0dBm, the divider resistors and the series resistor can all be increased in value until it does work.] Best regards, Charles "All electronics is analog." ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Practical considerations making a lab standard with an LTE lite
I once bought an HP16700 series logic analyzer off of Ebay that had a directory filled with porn on it... but that is a Unix machine. for good reason. A friend's scope picked up a virus. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
kb...@n1k.org said: > Maybe Tom needs a Microsoft Windows Update on his GPSDO firmware :) For some > reason the very thought of Microsoft getting involved in something like that > makes me shudder⦠For good reason. A friend's scope picked up a virus. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Said Jackson said: > Correct, and thats why its all a bad trade off if you have to use 50 Ohms > termination. Either more heat or more PN, and more circuitry. > So driving 50 Ohms inputs is not optimal here, 1M inputs are much better for > this purpose. That only works if you have a (very) short connection to the next stage. Things get interesting if you have, say, 10 feet of unterminated coax. 10 MHz is 100 ns, or 50 ns between transitions. Coax is ballpark of 5/8 c so that's 16 ns one way or 32 ns round drip. That's 60% of the heat as well as lots of nasty reflections. (Somebody please check my numbers.) -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Jim, 41 to 50dB is great. The height difference may be MSL to GPS height? Bye, Said Sent From iPhone > On Nov 24, 2014, at 18:39, Jim Sanford wrote: > > Said: > > I'm seeing C/No numbers between 50.0 and 41.0 for the "green" birds. I'm > seeing 27.0 to 42 on the "blue" birds. Not quite sure what the difference > between green and blue is. UBlox is acting kind of funny -- it ignores any > attempt to click on an icon or any of the menu bar items. Yet it lets me > move the various windows around and resize them. A challenge for another > day. (Winders7) > > HDOP is 1.0, which wikipedia tells me is "ideal". PDOP is 1.9, still good, > but far from ideal. Reported position is very stable, converting altitude > (meters) to feet gets me 1158 feet, about 120 feet lower than what the GPS in > the car says my antenna should be at. (1250' at the drive way, plus 20 feet > of pole supporting the antenna.) > > Jim > >> On 11/24/2014 8:27 PM, Said Jackson wrote: >> Jim, >> >> Bobs suggestion is good; look at for example the LT3060 for something that >> needs less than 100mA. >> >> Glad your antenna is working well. What C/No numbers is uBlox indicating? >> >> Bye, >> Said >> >> Sent from my iPad >> >>> On Nov 24, 2014, at 16:28, Bob Camp wrote: >>> >>> Hi >>> >>> The Linear LT1764 is a pretty good part. It’s nice and rugged / tough to >>> kill. Bypass the output with a few hundred uF of tantalum caps. Keep at >>> least a volt between input and output. >>> >>> Bob >>> On Nov 24, 2014, at 7:12 PM, Jim Sanford wrote: Said: Several times you've mentioned a low noise LDO regulator. I've not seen a device specified -- can you share? Also, yesterday, in response to my question about using an existing antenna, you basically said, "Try it." Well, I did -- working great for over 24 hours. At this moment, I have good lock on 9 GPS birds and a "3d/gps" fix mode reported by U-center. Interestingly, there are a few GPS birds that show up as blue, even though they have the same C/N ratio as some green birds. One of them is at 89 degrees elevation -- no blockage like some to the west -- don't get that. Anyway, wanted to share that my existing antenna seems to be working fine! AND, my first 10 MHZ board arrived today . . . . Thanks, Jim wb4...@amsat.org --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. > > > --- > This email has been checked for viruses by Avast antivirus software. > http://www.avast.com > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
It won't respond the LTE LITE is send only. I found another program from the Chip manufacturer and it behaves teh same as expected and mentioned by Said. So putty works as well as anything. OK my first external fun with the LTE. Since I had no 74AS74 I used a 74HC74 chip running at 4.5V. This allows it to operate with the 3.3V logic and act as an intermediate to a 5 volt logic family. The 4.5V is generated by a single diode drop with filter cap. I used both sections of the 74 so that 10 MHz and 5 Mhz are available. Now to do things like buffer and LPF the signals. An interesting comment from Bob. He suggests just using a traditional buffer logic chip then a LPF afterwords with a build out resistor to be able to drive coax. I may build that up using some buffers I have just to see how it works. I am thinking TTL just to tinker. Bob suggested an interesting chip bot they are SOT23 5 pin. Maybe I'll try that. But not at first. Regards Paul WB8TSL On Mon, Nov 24, 2014 at 9:39 PM, Jim Sanford wrote: > Said: > > I'm seeing C/No numbers between 50.0 and 41.0 for the "green" birds. I'm > seeing 27.0 to 42 on the "blue" birds. Not quite sure what the difference > between green and blue is. UBlox is acting kind of funny -- it ignores any > attempt to click on an icon or any of the menu bar items. Yet it lets me > move the various windows around and resize them. A challenge for another > day. (Winders7) > > HDOP is 1.0, which wikipedia tells me is "ideal". PDOP is 1.9, still > good, but far from ideal. Reported position is very stable, converting > altitude (meters) to feet gets me 1158 feet, about 120 feet lower than what > the GPS in the car says my antenna should be at. (1250' at the drive way, > plus 20 feet of pole supporting the antenna.) > > Jim > > > On 11/24/2014 8:27 PM, Said Jackson wrote: > >> Jim, >> >> Bobs suggestion is good; look at for example the LT3060 for something >> that needs less than 100mA. >> >> Glad your antenna is working well. What C/No numbers is uBlox indicating? >> >> Bye, >> Said >> >> Sent from my iPad >> >> On Nov 24, 2014, at 16:28, Bob Camp wrote: >> >> Hi >>> >>> The Linear LT1764 is a pretty good part. It’s nice and rugged / tough to >>> kill. Bypass the output with a few hundred uF of tantalum caps. Keep at >>> least a volt between input and output. >>> >>> Bob >>> >>> On Nov 24, 2014, at 7:12 PM, Jim Sanford wrote: Said: Several times you've mentioned a low noise LDO regulator. I've not seen a device specified -- can you share? Also, yesterday, in response to my question about using an existing antenna, you basically said, "Try it." Well, I did -- working great for over 24 hours. At this moment, I have good lock on 9 GPS birds and a "3d/gps" fix mode reported by U-center. Interestingly, there are a few GPS birds that show up as blue, even though they have the same C/N ratio as some green birds. One of them is at 89 degrees elevation -- no blockage like some to the west -- don't get that. Anyway, wanted to share that my existing antenna seems to be working fine! AND, my first 10 MHZ board arrived today . . . . Thanks, Jim wb4...@amsat.org --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts and follow the instructions there. >>> > > --- > This email has been checked for viruses by Avast antivirus software. > http://www.avast.com > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Said: I'm seeing C/No numbers between 50.0 and 41.0 for the "green" birds. I'm seeing 27.0 to 42 on the "blue" birds. Not quite sure what the difference between green and blue is. UBlox is acting kind of funny -- it ignores any attempt to click on an icon or any of the menu bar items. Yet it lets me move the various windows around and resize them. A challenge for another day. (Winders7) HDOP is 1.0, which wikipedia tells me is "ideal". PDOP is 1.9, still good, but far from ideal. Reported position is very stable, converting altitude (meters) to feet gets me 1158 feet, about 120 feet lower than what the GPS in the car says my antenna should be at. (1250' at the drive way, plus 20 feet of pole supporting the antenna.) Jim On 11/24/2014 8:27 PM, Said Jackson wrote: Jim, Bobs suggestion is good; look at for example the LT3060 for something that needs less than 100mA. Glad your antenna is working well. What C/No numbers is uBlox indicating? Bye, Said Sent from my iPad On Nov 24, 2014, at 16:28, Bob Camp wrote: Hi The Linear LT1764 is a pretty good part. It’s nice and rugged / tough to kill. Bypass the output with a few hundred uF of tantalum caps. Keep at least a volt between input and output. Bob On Nov 24, 2014, at 7:12 PM, Jim Sanford wrote: Said: Several times you've mentioned a low noise LDO regulator. I've not seen a device specified -- can you share? Also, yesterday, in response to my question about using an existing antenna, you basically said, "Try it." Well, I did -- working great for over 24 hours. At this moment, I have good lock on 9 GPS birds and a "3d/gps" fix mode reported by U-center. Interestingly, there are a few GPS birds that show up as blue, even though they have the same C/N ratio as some green birds. One of them is at 89 degrees elevation -- no blockage like some to the west -- don't get that. Anyway, wanted to share that my existing antenna seems to be working fine! AND, my first 10 MHZ board arrived today . . . . Thanks, Jim wb4...@amsat.org --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Jim, Bobs suggestion is good; look at for example the LT3060 for something that needs less than 100mA. Glad your antenna is working well. What C/No numbers is uBlox indicating? Bye, Said Sent from my iPad On Nov 24, 2014, at 16:28, Bob Camp wrote: > Hi > > The Linear LT1764 is a pretty good part. It’s nice and rugged / tough to > kill. Bypass the output with a few hundred uF of tantalum caps. Keep at least > a volt between input and output. > > Bob > >> On Nov 24, 2014, at 7:12 PM, Jim Sanford wrote: >> >> Said: >> >> Several times you've mentioned a low noise LDO regulator. I've not seen a >> device specified -- can you share? >> >> Also, yesterday, in response to my question about using an existing antenna, >> you basically said, "Try it." Well, I did -- working great for over 24 >> hours. At this moment, I have good lock on 9 GPS birds and a "3d/gps" fix >> mode reported by U-center. Interestingly, there are a few GPS birds that >> show up as blue, even though they have the same C/N ratio as some green >> birds. One of them is at 89 degrees elevation -- no blockage like some to >> the west -- don't get that. >> >> Anyway, wanted to share that my existing antenna seems to be working fine! >> >> AND, my first 10 MHZ board arrived today . . . . >> >> Thanks, >> Jim >> wb4...@amsat.org >> >> >> --- >> This email has been checked for viruses by Avast antivirus software. >> http://www.avast.com >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Hi The Linear LT1764 is a pretty good part. It’s nice and rugged / tough to kill. Bypass the output with a few hundred uF of tantalum caps. Keep at least a volt between input and output. Bob > On Nov 24, 2014, at 7:12 PM, Jim Sanford wrote: > > Said: > > Several times you've mentioned a low noise LDO regulator. I've not seen a > device specified -- can you share? > > Also, yesterday, in response to my question about using an existing antenna, > you basically said, "Try it." Well, I did -- working great for over 24 > hours. At this moment, I have good lock on 9 GPS birds and a "3d/gps" fix > mode reported by U-center. Interestingly, there are a few GPS birds that > show up as blue, even though they have the same C/N ratio as some green > birds. One of them is at 89 degrees elevation -- no blockage like some to > the west -- don't get that. > > Anyway, wanted to share that my existing antenna seems to be working fine! > > AND, my first 10 MHZ board arrived today . . . . > > Thanks, > Jim > wb4...@amsat.org > > > --- > This email has been checked for viruses by Avast antivirus software. > http://www.avast.com > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Said: Several times you've mentioned a low noise LDO regulator. I've not seen a device specified -- can you share? Also, yesterday, in response to my question about using an existing antenna, you basically said, "Try it." Well, I did -- working great for over 24 hours. At this moment, I have good lock on 9 GPS birds and a "3d/gps" fix mode reported by U-center. Interestingly, there are a few GPS birds that show up as blue, even though they have the same C/N ratio as some green birds. One of them is at 89 degrees elevation -- no blockage like some to the west -- don't get that. Anyway, wanted to share that my existing antenna seems to be working fine! AND, my first 10 MHZ board arrived today . . . . Thanks, Jim wb4...@amsat.org --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
We should not forget that the LTE is not a free standing frequency source: it is steered to GPS signals and, in the long term, will reflect the accuracy of GPS and the stability of the as-received signal. >From the ADEV plot in the user manual, it looks like the time constant for steering of the TCXO is about one minute; constructing an enclosure with a time constant significant longer than a few minutes has diminishing returns. Mike -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Poul-Henning Kamp Sent: Sunday, November 23, 2014 8:33 AM To: Discussion of precise time and frequency measurement; Charles Steinmetz Subject: Re: [time-nuts] Practical considerations making a lab standard with an LTE lite In message <20141123153744.biokf...@smtp16.mail.yandex.net>, Charles Steinmetz writes: >First, mount the LTE in a cast aluminum box (not thin sheet metal, >something with some heft). [...] Charles' design has some good points, but I don't agree with it. What you are trying to do is to low-pass filter any thermal signals before they reach the LTE or OCXO. Charles' design works great from the outside, but doesn't do anything with respect to the thermal energy expended by the encapsulated device themselves, which will cause convection in the inner box. (For LTE and OCXO it is probably less of a problem that changing power-disipation will have a outsized effect on the central temperature.) Here is a much simpler and likely cheaper way to do it: Put the LTE or OCXO in a small box of your choice. Even a cardboard box is fine. A little thermal insulation in the box is OK, but not too much, the heat must be able to get out. Find a medium sized cardboard box, something like a cubic feet or so. Place it where you want your house-standard, with some kind of thermal insulation under it, two layers of old rug will do fine. Lay a floor of bricks inside the box. Build a "wall" of bricks along the outside of the box. Place the smaller box in the hole in the middle, cut the corner of a brick to run the cables without too much leakage. Use a floortile as roof, possibly with a layer of bricks on top. Close the outher cardboard box with tape to minimize convection. Congratulations, you now have a cheap and incredibly efficient thermal low-pas filter, which will allow thermal energy to move in both directions -- eventually. The outher cardboard box is not optional, unless you replace it with some other "mostly air-tight" barrier. The little bit of insulation the outher cardboard adds are not a bad idea either, for instance it reduces the effect of sunlight hits the box at certain times of the day/year. But you can substitute any geological building material you have at hand for the bricks, because the trick is that geological building materials have just the right thermal properties we are looking for: Decent but not too good thermal conductivity with healthy dose of thermal mass. Cinderblocks comes with convenient interior holes premade. Aerated concrete blocks are also a candidate material but don't make it too thick since it insulates quite well, and paint the surface to bind the dust. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Correct, and thats why its all a bad trade off if you have to use 50 Ohms termination. Either more heat or more PN, and more circuitry. So driving 50 Ohms inputs is not optimal here, 1M inputs are much better for this purpose. I had discussed the advantages of CMOS open-ended termination some months ago here in detail.. Sent From iPhone > On Nov 24, 2014, at 5:32, "Dr. David Kirkby (Kirkby Microwave Ltd)" > wrote: > > On 24 November 2014 at 03:44, Said Jackson via time-nuts > wrote: >> On the 20MHz units there is already a strong buffer that can drive 50 Ohms >> terminations so adding a buffer in front of the coax connector on that >> version would have just added unnecessary phase and AM noise, parts count >> and cost, and power consumption, and would have resulted in a product with >> worse performance than we have now. > > IIRC you said that using this will generate more heat on the board > near the crystal. > >> Bye, >> Said > > Dave ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
On 24 November 2014 at 03:44, Said Jackson via time-nuts wrote: > On the 20MHz units there is already a strong buffer that can drive 50 Ohms > terminations so adding a buffer in front of the coax connector on that > version would have just added unnecessary phase and AM noise, parts count and > cost, and power consumption, and would have resulted in a product with worse > performance than we have now. IIRC you said that using this will generate more heat on the board near the crystal. > Bye, > Said Dave ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
In message <54723237.7070...@pcscons.com>, Alex Pummer writes: >by us in central California, we get 1kW/h square meter average around >the year, the south even more, el Cajon will have today +29C° in the >afternoon as of 23 of November 2014 Yes, the latitude means a lot for ground heating, both in terms of Sun radiation angle and length of winter. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Charles, Any buffer options added to the board would have caused either additive phase noise or added power consumption, and possibly yet another low noise LDO to be required. On the 20MHz units there is already a strong buffer that can drive 50 Ohms terminations so adding a buffer in front of the coax connector on that version would have just added unnecessary phase and AM noise, parts count and cost, and power consumption, and would have resulted in a product with worse performance than we have now. That configuration is the "normal" one so we did not add unnecessary circuitry that would have decreased product performance. On the 10MHz boards with external DIP-14 TCXO there is no buffer, and adding one would have required to possibly add yet another low noise supply regulator and possibly another MMCX connector. Since this is the "optional" configuration, we optimized for highest performance for the "standard" configuration. Adding this many features to the board required some trade offs to be made, and we have to keep in mind the initial goal of the entire effort: to provide an easy way to evaluate the performance of our LTE Lite module - hence its called the LTE Lite Evaluation board. Everything else was a bonus. But in the end it should be fairly trivial to put a 50 Ohms driver and low pass filter together using either a CMOS gate or a simple emitter follower. We also need to keep in mind that generating a Sine Wave output would have consumed 200mW to 250mW additive power and thus would have more than doubled the total power consumption. Lastly we have three outputs on the board so we would have required three additional buffers and their support circuitry, all that for a questionable improvement. Or instead of adding a bunch of buffers one can use somewhat short cables and 1M input impedance on the target hardware and that will work perfectly too without any changes.. Bye, Said Sent From iPhone > On Nov 23, 2014, at 16:22, Charles Steinmetz wrote: > > Said wrote: > >> The 10MHz units have a different RF output than the 20MHz units. The >> 20MHz units have a 50 Ohms series-terminated and buffered RF output, while >> the >> 10MHz units have the TCXO output drive the MMCX connector directly without >> series impedance matching. Both drive the line with 3.0V CMOS levels. This >> means the cable on the 10MHz unit should be kept as short as possible, and >> that impedance matching for maximum power-transfer is not required nor >> desired. The suggestion that Charles made for checking the impedance by >> progressively loading the output more and more is valid for Sine Wave >> outputs, but >> not for CMOS outputs as implemented on the LTE Lite. > > Absolutely correct -- I did not anticipate that anyone would make unbuffered > logic levels available to the external world. > > In that case, I'd put a logic-level line driver immediately at the unit (by > immediately, I mean with a small breakout card that plugs directly onto the > LTE's MMCX connector with no intervening cable). For example, all 6 outputs > of an HC14 or AC14 hex inverter connected in parallel, or a dedicated line > driver chip like an HC365/366 or AC240/244/540/541. > > The buffer should be inside the enclosure with the LTE, and I would also add > a T-network filter to convert the logic-level square wave into a sine wave. > This would confine all of the fast logic transitions inside the shielded box, > where they can do the least mischief. > > For the T-network, I like 10uH/50.5pF/10uH, others like 1.5uH/310pF/1.5uH. > Both draw ~ +/- 35mA from a 5v logic output. Make sure your buffer can > supply this current, and feed the T-network through 10nF and 50 ohms in > series. You'll get a 1Vrms (13dBm) sine wave into 50 ohms (675mVrms with 3v > logic). H3 is down 40dBc with the 1.5uH network and 60dBc with the 10uH > network. [Note that the apparent source impedance is > 50 ohms, so the > open-circuit voltage is more than double.] > > Best regards, > > Charles > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
On 11/23/14, 5:46 PM, Brooke Clarke wrote: Hi Jim: It turns out that ground water that's being pumped is very similar to pumping oil. It's a limited resource. There's a web page showing the GRACE satellite maps of California and that we are running out of ground water. Back east where that data is from, I suspect that's not a big an issue. Water is many tens of meters down in most of California. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Hi Jim: It turns out that ground water that's being pumped is very similar to pumping oil. It's a limited resource. There's a web page showing the GRACE satellite maps of California and that we are running out of ground water. This isn't the page, but gives the idea: http://www.cnyo.org/2014/08/19/nasa-space-place-droughts-floods-and-the-earths-gravity-by-the-grace-of-nasa/ So depending on ground water as a stable heat sink may no longer be an option as wells go dry. It's been many years since the local water company has quit installing new meters. Mail_Attachment -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html http://www.prc68.com/I/DietNutrition.html Jim Lux wrote: On 11/23/14, 11:15 AM, Alex Pummer wrote: by us in central California, we get 1kW/h square meter average around the year, the south even more, el Cajon will have today +29C° in the afternoon as of 23 of November 2014 I suspect more like the insolation peaks at 1kW/square meter or a bit more, the average over a day is somewhat less. At JPL we have a weather station on line that displays this and I don't recall seeing significantly more than 1000 W/m2. The nominal average 1.362 kW/sq meter at solar max is at the top of the atmosphere, and is normal to the incidence. The surface insolation at the equator when the sun is directly overhead is about 1.04 kW/sq meter. I think you'd get pretty close to that at solar noon in the Summer in Southern California, which is 32-34 degrees latitude, so at the solstice, the zenith angle is 10 degrees, and cos(10) is pretty close to 1. You do pick up some additional insolation from diffuse and scattered radiation from clouds or haze, but I'm not sure that makes up for the attenuation due to the same haze. Some time ago, I calculated that in Los Angeles (34 degrees latitude), a horizontal flat plate gets about 8-9 kWh/m2/day in summer and about 1-2 kWh/m2/day in winter.. Tilting the collector would help a lot in the winter (Zenith angle is 56 degrees instead of 10), but there's no making up for the short days. Getting back to the time-nuts aspects, there are some charts around that show the temperature variation as a function of depth, latitude, soil and season. I know that for DSN, they went through all kinds of gyrations to calculate (and measure) this for the optical fiber timing links between the antennas and the masers. For small dissipated power (I doubt your oscillator is going to be putting kilowatts into the soil) you don't have to go very deep (single digit meters) before the diurnal variation is down in the 0.1 degree or smaller. Annual variations are bigger. http://www.builditsolar.com/Projects/Cooling/EarthTemperatures.htm has a bunch of charts for some unknown latitude (probably mid Atlantic states, since the data is from Virginia Tech). They appear to use well water temperatures as the measurement technique. A bit more googling found a paper by one G. Florides that refers to the Kasuda formula.. (the link is hard to cut and paste.. I'm sure if you google "Florides soil temperature" you'll find it) and gives this reference Kasuda, T., and Archenbach, P.R. "Earth Temperature and Thermal Diffusivity at Selected Stations in the United States", ASHRAE Transactions, Vol. 71, Part 1, 1965. Horizontal ground heat means that you are harvesting sunshine accumulated in the top one meter of the soil. Much of the energy is harvested from freezing the water around the pipe thus pulling out the relatively high melting energy of water. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Said wrote: The 10MHz units have a different RF output than the 20MHz units. The 20MHz units have a 50 Ohms series-terminated and buffered RF output, while the 10MHz units have the TCXO output drive the MMCX connector directly without series impedance matching. Both drive the line with 3.0V CMOS levels. This means the cable on the 10MHz unit should be kept as short as possible, and that impedance matching for maximum power-transfer is not required nor desired. The suggestion that Charles made for checking the impedance by progressively loading the output more and more is valid for Sine Wave outputs, but not for CMOS outputs as implemented on the LTE Lite. Absolutely correct -- I did not anticipate that anyone would make unbuffered logic levels available to the external world. In that case, I'd put a logic-level line driver immediately at the unit (by immediately, I mean with a small breakout card that plugs directly onto the LTE's MMCX connector with no intervening cable). For example, all 6 outputs of an HC14 or AC14 hex inverter connected in parallel, or a dedicated line driver chip like an HC365/366 or AC240/244/540/541. The buffer should be inside the enclosure with the LTE, and I would also add a T-network filter to convert the logic-level square wave into a sine wave. This would confine all of the fast logic transitions inside the shielded box, where they can do the least mischief. For the T-network, I like 10uH/50.5pF/10uH, others like 1.5uH/310pF/1.5uH. Both draw ~ +/- 35mA from a 5v logic output. Make sure your buffer can supply this current, and feed the T-network through 10nF and 50 ohms in series. You'll get a 1Vrms (13dBm) sine wave into 50 ohms (675mVrms with 3v logic). H3 is down 40dBc with the 1.5uH network and 60dBc with the 10uH network. [Note that the apparent source impedance is > 50 ohms, so the open-circuit voltage is more than double.] Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Hi I believe that if you go back a few years in the archives, you will find a thread that ultimately stops with a swimming pool full of mercury. Needless to say, we’re been down this road once or twice before. Bob > On Nov 23, 2014, at 7:59 PM, Neville Michie wrote: > > A Hint about avoiding convective cell heat transfer, > If you keep the spacing between two planes less than 5/16" then you will > be unlikely to have convection cells forming. The stationary air is a good > insulator > but thermal radiation will be the dominant heat transfer process. > This is true for double glazing, katharometers and generally all devices. > The suppression of turbulent heat transfer may provide more insulation but > also > less noise and instability. > So it may be a good idea to use a relatively close fitting box with thick > walls. > Cheers, > Neville Michie > > > > > On 23/11/2014, at 11:37 PM, Charles Steinmetz wrote: > >> Dave wrote >> >>> But given the TCXO"s sensitivity to temperature changes, I don't >>> know whether it might be preferable to mount the LTE lite in its own box >>> without any power supplies in it - perhaps with some thermally insulting >>> material around the LTE lite so the crystal doesn't experience any fast >>> temperature changes. >> >> First, mount the LTE in a cast aluminum box (not thin sheet metal, something >> with some heft). Use thermally insulating standoffs (teflon or nylon, with >> no metal "through" fasteners) to get the board in the middle of the volume >> of the box. Use a box a bit larger than you'd first think, so there is at >> least 1" of air on all 6 sides of the LTE board. Do NOT mount any part of >> the LTE board (connectors, etc.) directly to the box walls -- use "pigtails" >> for all connections. Do NOT use any insulation between the LTE and the box >> walls other than the 1"+ of air. >> >> The mounting described above will add substantial thermal capacitance to the >> LTE board (good) without adding significant thermal resistance (bad). For >> further discussions of this issue, search the list archives for "thermal >> capacitance" and "thermal mass." >> >> Now, mount the cast box (plus any thermal mass you add to it -- see below) >> so that IT is thermally isolated from the overall enclosure (or, if it sits >> out in the open, thermally isolated from anything solid). The air space in >> the enclosure isolates the oscillator from the cast box and the box is >> sufficiently massive that its temperature cannot change nearly as fast as >> ambient. The thermal mass of the cast box can be adjusted by adding thermal >> mass to it as desired. >> >> The goal is for the box temperature to change only by changes in ambient AIR >> temperature, and the LTE board to change only by changes in the AIR >> temperature inside the cast box. This integrates any changes to the LTE >> board temperature with a very long time constant, which allows the GPS >> discipline to track and cancel the temperature changes. >> >> (If you mount an ovenized oscillator this same way, it integrates any >> changes to the OCXO temperature so that the oven control loop can track and >> cancel any changes to the crystal temperature.) >> >> You can, of course, improve things even further by making sure the ambient >> air temperature surrounding the cast box changes slowly, or not at all. But >> the technique described above can be counted on to reduce thermal effects in >> most OCXOs or GPSDOs to better (often much better) than the 1e-13 level >> unless the ambient temperature changes MUCH more and MUCH faster than any >> change we wouild consider normal for a living space. This is true whether >> the cast box is mounted out in the open, or inside an overall enclosure with >> other electronics. >> >> Best regards, >> >> Charles >> >> >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
A Hint about avoiding convective cell heat transfer, If you keep the spacing between two planes less than 5/16" then you will be unlikely to have convection cells forming. The stationary air is a good insulator but thermal radiation will be the dominant heat transfer process. This is true for double glazing, katharometers and generally all devices. The suppression of turbulent heat transfer may provide more insulation but also less noise and instability. So it may be a good idea to use a relatively close fitting box with thick walls. Cheers, Neville Michie On 23/11/2014, at 11:37 PM, Charles Steinmetz wrote: > Dave wrote > >> But given the TCXO"s sensitivity to temperature changes, I don't >> know whether it might be preferable to mount the LTE lite in its own box >> without any power supplies in it - perhaps with some thermally insulting >> material around the LTE lite so the crystal doesn't experience any fast >> temperature changes. > > First, mount the LTE in a cast aluminum box (not thin sheet metal, something > with some heft). Use thermally insulating standoffs (teflon or nylon, with > no metal "through" fasteners) to get the board in the middle of the volume of > the box. Use a box a bit larger than you'd first think, so there is at least > 1" of air on all 6 sides of the LTE board. Do NOT mount any part of the LTE > board (connectors, etc.) directly to the box walls -- use "pigtails" for all > connections. Do NOT use any insulation between the LTE and the box walls > other than the 1"+ of air. > > The mounting described above will add substantial thermal capacitance to the > LTE board (good) without adding significant thermal resistance (bad). For > further discussions of this issue, search the list archives for "thermal > capacitance" and "thermal mass." > > Now, mount the cast box (plus any thermal mass you add to it -- see below) so > that IT is thermally isolated from the overall enclosure (or, if it sits out > in the open, thermally isolated from anything solid). The air space in the > enclosure isolates the oscillator from the cast box and the box is > sufficiently massive that its temperature cannot change nearly as fast as > ambient. The thermal mass of the cast box can be adjusted by adding thermal > mass to it as desired. > > The goal is for the box temperature to change only by changes in ambient AIR > temperature, and the LTE board to change only by changes in the AIR > temperature inside the cast box. This integrates any changes to the LTE > board temperature with a very long time constant, which allows the GPS > discipline to track and cancel the temperature changes. > > (If you mount an ovenized oscillator this same way, it integrates any changes > to the OCXO temperature so that the oven control loop can track and cancel > any changes to the crystal temperature.) > > You can, of course, improve things even further by making sure the ambient > air temperature surrounding the cast box changes slowly, or not at all. But > the technique described above can be counted on to reduce thermal effects in > most OCXOs or GPSDOs to better (often much better) than the 1e-13 level > unless the ambient temperature changes MUCH more and MUCH faster than any > change we wouild consider normal for a living space. This is true whether > the cast box is mounted out in the open, or inside an overall enclosure with > other electronics. > > Best regards, > > Charles > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
On 11/23/14, 11:15 AM, Alex Pummer wrote: by us in central California, we get 1kW/h square meter average around the year, the south even more, el Cajon will have today +29C° in the afternoon as of 23 of November 2014 I suspect more like the insolation peaks at 1kW/square meter or a bit more, the average over a day is somewhat less. At JPL we have a weather station on line that displays this and I don't recall seeing significantly more than 1000 W/m2. The nominal average 1.362 kW/sq meter at solar max is at the top of the atmosphere, and is normal to the incidence. The surface insolation at the equator when the sun is directly overhead is about 1.04 kW/sq meter. I think you'd get pretty close to that at solar noon in the Summer in Southern California, which is 32-34 degrees latitude, so at the solstice, the zenith angle is 10 degrees, and cos(10) is pretty close to 1. You do pick up some additional insolation from diffuse and scattered radiation from clouds or haze, but I'm not sure that makes up for the attenuation due to the same haze. Some time ago, I calculated that in Los Angeles (34 degrees latitude), a horizontal flat plate gets about 8-9 kWh/m2/day in summer and about 1-2 kWh/m2/day in winter.. Tilting the collector would help a lot in the winter (Zenith angle is 56 degrees instead of 10), but there's no making up for the short days. Getting back to the time-nuts aspects, there are some charts around that show the temperature variation as a function of depth, latitude, soil and season. I know that for DSN, they went through all kinds of gyrations to calculate (and measure) this for the optical fiber timing links between the antennas and the masers. For small dissipated power (I doubt your oscillator is going to be putting kilowatts into the soil) you don't have to go very deep (single digit meters) before the diurnal variation is down in the 0.1 degree or smaller. Annual variations are bigger. http://www.builditsolar.com/Projects/Cooling/EarthTemperatures.htm has a bunch of charts for some unknown latitude (probably mid Atlantic states, since the data is from Virginia Tech). They appear to use well water temperatures as the measurement technique. A bit more googling found a paper by one G. Florides that refers to the Kasuda formula.. (the link is hard to cut and paste.. I'm sure if you google "Florides soil temperature" you'll find it) and gives this reference Kasuda, T., and Archenbach, P.R. "Earth Temperature and Thermal Diffusivity at Selected Stations in the United States", ASHRAE Transactions, Vol. 71, Part 1, 1965. Horizontal ground heat means that you are harvesting sunshine accumulated in the top one meter of the soil. Much of the energy is harvested from freezing the water around the pipe thus pulling out the relatively high melting energy of water. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
by us in central California, we get 1kW/h square meter average around the year, the south even more, el Cajon will have today +29C° in the afternoon as of 23 of November 2014 73 Alex On 11/23/2014 9:49 AM, Poul-Henning Kamp wrote: In message , "Dr. David Kirkby (Kirkby Microwave Ltd)" writes: He installs ground source heat pumps for the geothermal energy. He says that they actually work quite poorly in many cases. There is a BIG difference between geothermal and ground heating. Geothermal means you drill at least 50m (Iceland) or more likely half a kilometer down, in order to harvest water at near boiling point from the Earths geological heat-sources (mostly uranium decay). Extracting more energy than available just means the temperature drops temporarily. It will increase again once you reduce the pump rate. Horizontal ground heat means that you are harvesting sunshine accumulated in the top one meter of the soil. Much of the energy is harvested from freezing the water around the pipe thus pulling out the relatively high melting energy of water. If you extract more energy than you deposit sunshine, you end up freezing a larger and larger volume of water/soil around the pipe and your compressor will eat a lot of electricity. In practice it looks like this: http://ing.dk/artikel/varmepumpe-mareridt-jordslange-var-dybfrossen-i-maj-113176 (The two pictures show the same pipe, with and without frozen ground.) Finally there is vertial ground heat where you drill down only about 40-80 meter, tapping heat mostly from ground water resources.Most places the ground water doesn't move fast enough to deliver the amounts of energy extracted, and over time the source returns unusably low temperature and must be abandonned. Typically after 25-30 years. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Hi Actually that was Bob trying to explain Tom’s plots simply from looking at them. I *think* I got it right, but it’s Tom’s data and his LTE part. Others have commented that Tom’s part looks different than theirs. Maybe Tom needs a Microsoft Windows Update on his GPSDO firmware :) For some reason the very thought of Microsoft getting involved in something like that makes me shudder… Bob > On Nov 23, 2014, at 5:33 PM, Said Jackson via time-nuts > wrote: > > Tom, > > From the looks of the plots these may be from the first proto unit with early > software no? Also was this with the indoor GPS antenna setup? > > The production units with outdoor or windowed' antenna should have > significantly improved average performance from the first unit and its early > GPS and GPSDO firmware versions. > > Bye, > Said > > Sent From iPhone > >> On Nov 23, 2014, at 14:18, Bob Camp wrote: >> >> Hi >> >> There are two plots with activity changing at 300 seconds. The second plot >> (purple) is the removal of the paper at 300 seconds. The fourth plot (red) >> is the addition of the paper at 300 seconds. >> >> The last plot (green and blue) is ADEV with and without the paper. Blue is >> ADEV with paper. Green is ADEV without paper. >> >> The second to last plot demonstrates the unit meeting 1x10^-9 (peak to peak) >> frequency stability with the paper over a 1,000 second test. It shows it >> doing about 5X worse on frequency stability over the same period without the >> paper. Yes, that’s all with 1 second averaging. Changing the averaging would >> impact each of the results. It should change their ratio. >> >> Again back to the basic question: frequency over what period? Go to a 24 >> hour average and the results should be terrific. In some systems, that’s a >> useful number (I guess….). I rarely see people set their counters to an >> 86,000 second gate time :) >> >> Bob >> >> >>> On Nov 23, 2014, at 4:42 PM, Dr. David Kirkby (Kirkby Microwave Ltd) >>> wrote: >>> >>> On 23 Nov 2014 16:25, "Tom Van Baak" wrote: >>> For plots and photos showing performance with, and without, and with >>> insulation see: http://leapsecond.com/pages/LTE-Lite/ The difference is dramatic, especially if you are used to working with >>> OCXO where this sort of effect does not occur. >>> >>> Tom, >>> >>> What plots are with and without the thermal paper? >>> >>> I see several graphs, but don't know what is under what conditions. >>> >>> The second graph shows something fairly significant happening at 300 s. Is >>> that where you removed the TP? >>> >>> Dave >>> ___ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Hi A lot of these parts are designed for use in a system environment rather than sitting out on a bench. That’s as true of the KS boxes (forced air cooling) as it is of the LTE’s. In > 90% (and likely > 99.9%) of the places a TCXO gets used, it’s packed tight in with a bunch of other stuff. Not only is there no air movement, there might not be much air. A cell phone is a good example of this sort of assembly. Other battery powered portable gear fit this same general model, but possibly not to the same degree of “cram it in". Yes, we love our big rack mounted boxes full of this or that. They are useful. The TCXO guys would go broke quickly if that was the market they focused their main efforts on. Big Morion 2” x 2” x 1” OCXO’s, yes those are targeted more at big rack mount this or that. Different market focus for different products. It’s not a one size fits all world. Indeed, adapting a TCXO to a bench environment is something that you need to do. A nice fluffy cotton towel works quite well. Yes, that’s a 1970’s solution to the problem. Most TCXO’s were bigger back then. The issue has been around “for a while”. It’s actually not a bad thing to keep handy when testing OCXO’s. If they don’t work you can always use it to cry into …:) Bob > On Nov 23, 2014, at 11:24 AM, Tom Van Baak wrote: > > The short-term performance is 10x worse if you don't shield the TCXO from > air, even if the ambient air is "still". I suggested Said sell the product > with some sort of engineered shield in place. Instead each of us will solve > the problem in our own way; which is ok for a dev kit. > > For plots and photos showing performance with, and without, and with > insulation see: > http://leapsecond.com/pages/LTE-Lite/ > The difference is dramatic, especially if you are used to working with OCXO > where this sort of effect does not occur. > > The insulation may be found in convenient rolls at many local stores. I used > TP, which for this application is an acronym for Thermal Paper. > > /tvb > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Tom, >From the looks of the plots these may be from the first proto unit with early >software no? Also was this with the indoor GPS antenna setup? The production units with outdoor or windowed' antenna should have significantly improved average performance from the first unit and its early GPS and GPSDO firmware versions. Bye, Said Sent From iPhone > On Nov 23, 2014, at 14:18, Bob Camp wrote: > > Hi > > There are two plots with activity changing at 300 seconds. The second plot > (purple) is the removal of the paper at 300 seconds. The fourth plot (red) is > the addition of the paper at 300 seconds. > > The last plot (green and blue) is ADEV with and without the paper. Blue is > ADEV with paper. Green is ADEV without paper. > > The second to last plot demonstrates the unit meeting 1x10^-9 (peak to peak) > frequency stability with the paper over a 1,000 second test. It shows it > doing about 5X worse on frequency stability over the same period without the > paper. Yes, that’s all with 1 second averaging. Changing the averaging would > impact each of the results. It should change their ratio. > > Again back to the basic question: frequency over what period? Go to a 24 hour > average and the results should be terrific. In some systems, that’s a useful > number (I guess….). I rarely see people set their counters to an 86,000 > second gate time :) > > Bob > > >> On Nov 23, 2014, at 4:42 PM, Dr. David Kirkby (Kirkby Microwave Ltd) >> wrote: >> >> On 23 Nov 2014 16:25, "Tom Van Baak" wrote: >> >>> For plots and photos showing performance with, and without, and with >> insulation see: >>> http://leapsecond.com/pages/LTE-Lite/ >>> The difference is dramatic, especially if you are used to working with >> OCXO where this sort of effect does not occur. >> >> Tom, >> >> What plots are with and without the thermal paper? >> >> I see several graphs, but don't know what is under what conditions. >> >> The second graph shows something fairly significant happening at 300 s. Is >> that where you removed the TP? >> >> Dave >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Hi There are two plots with activity changing at 300 seconds. The second plot (purple) is the removal of the paper at 300 seconds. The fourth plot (red) is the addition of the paper at 300 seconds. The last plot (green and blue) is ADEV with and without the paper. Blue is ADEV with paper. Green is ADEV without paper. The second to last plot demonstrates the unit meeting 1x10^-9 (peak to peak) frequency stability with the paper over a 1,000 second test. It shows it doing about 5X worse on frequency stability over the same period without the paper. Yes, that’s all with 1 second averaging. Changing the averaging would impact each of the results. It should change their ratio. Again back to the basic question: frequency over what period? Go to a 24 hour average and the results should be terrific. In some systems, that’s a useful number (I guess….). I rarely see people set their counters to an 86,000 second gate time :) Bob > On Nov 23, 2014, at 4:42 PM, Dr. David Kirkby (Kirkby Microwave Ltd) > wrote: > > On 23 Nov 2014 16:25, "Tom Van Baak" wrote: > >> For plots and photos showing performance with, and without, and with > insulation see: >> http://leapsecond.com/pages/LTE-Lite/ >> The difference is dramatic, especially if you are used to working with > OCXO where this sort of effect does not occur. > > Tom, > > What plots are with and without the thermal paper? > > I see several graphs, but don't know what is under what conditions. > > The second graph shows something fairly significant happening at 300 s. Is > that where you removed the TP? > > Dave > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Hi Well the answer is obvious:) You simply need to turn on the air-conditioning full blast for more months of the summer in … ummm ….. e …. Denmark … hmmm….. Heat only or cool only systems seem to be more practical when the heat sink is a flowing body of water or an ocean. Unfortunately those seem to also run up the price of adjacent real estate. Moving bodies of water also aren’t very good for stabilizing temperature on a frequency source. The same thing is true of a hole in the ground that goes above or below the level of ground water over the course of the year. If you drill a hole, there is indeed a wrong depth to pick. It might be interesting to see how deep you need to go for stable ground water temps. Around here the top layer of ground water was rain last week or last month. Bob > On Nov 23, 2014, at 1:07 PM, Poul-Henning Kamp wrote: > > > In message > > , "Dr. David Kirkby (Kirkby Microwave Ltd)" writes: > >>> Geothermal means you drill at least 50m (Iceland) or more likely >>> half a kilometer down, in order to harvest water at near boiling >>> point from the Earths geological heat-sources (mostly uranium decay). >> >> Sorry. What he installs is pipes in the ground in residential or >> industrial sites. Basically he says they work initially, but performance >> drops dramatically over a couple of years. > > That is not "geothermal" then, and yes, a LOT of those systems are > badly underdimensioned. > > I've been researching this topic intensively because my new house > will be heated that way. > > My conclusion, based on reading a lot of reports, is that there > is no credible way to predict the performance. The wetter your > soil the better, but that's about it. > > I'm going to overprovision by a factor two to be on the safe side, > afterall it only costs EUR7 for each extra meter of pipe. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
On 23 Nov 2014 16:25, "Tom Van Baak" wrote: > For plots and photos showing performance with, and without, and with insulation see: >http://leapsecond.com/pages/LTE-Lite/ > The difference is dramatic, especially if you are used to working with OCXO where this sort of effect does not occur. Tom, What plots are with and without the thermal paper? I see several graphs, but don't know what is under what conditions. The second graph shows something fairly significant happening at 300 s. Is that where you removed the TP? Dave ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Hi If your target frequency error is in the < 1x10^-10 to the “hopefully 1x10^-11” range, You should consider your very requirements carefully. I tossed up some frequency plots of the KS boxes and of the Z3801 a while back. They are OCXO based boxes running in a very good thermal environment. Their OCXO’s ADEV is roughly 1x10^-12 at 1 to 10 seconds. That compares directly to the TCXO’s apparent ADEV posted by Tom earlier at 5x10^-11 in the 1 to 10 second region. The OCXO based parts (with a very loose interpretation of 1x10^-11 frequency accuracy) do not hit < +/- 1x10^-11 frequency accuracy. If the plots are to far back to dig up, I can re-post them. They will hit a < 1x10^-10 frequency accuracy limit without any quibbling over the definition of the spec. The frequency accuracy of a TCXO based part is not going to measure up to an OCXO based part. That’s not because the TCXO part is in some way flawed, it’s just the way things work on a GPSDO. If you are going with a TCXO, concrete bunker construction is not needed. With an OCXO based part, it just might help a bit. This may be a bit counter intuitive. It’s a function of where the (much better) ADEV of the OCXO intersects the (constant slope) ADEV of the GPS receiver. The control loop on the OCXO based part will be running at a *much* longer time constant. If the OCXO ADEV is 10X better, it will be 10X longer. If it’s 100X better it will be 100X longer. In both cases (TCXO and OCXO) the ADEV at 1 or even 10 seconds will not be improved by thermal this or that , once drafts are eliminated. The filter will still track where it needs to track. If the OCXO is running a filter out at a thousand seconds, you will *will* see slow thermal variations. The TCXO based part’s output running at (say) 10 seconds will not see the same variations, they will be corrected out by the GPS before they hit the output. — Why tie these things together? Where you wind up depends very much on where you are headed. Starting with the right gear for the application will matter in the end. Putting a lot of effort into a project without considering the ultimate goal may not be as economical as it could otherwise be. Bob > On Nov 23, 2014, at 3:04 PM, Jim Sanford wrote: > > All: > > I appreciate all the responses to my post earlier today. Very informative. > > First: DownEast Microwave sells a nice kit for distributing 10 MHz. Specs > are on their website, but basically, one in, four out -- each individually > buffered and filtered. > > Second: I will use the 20 MHz from the LTE-Lite to lock a 100Mhz TCXO which > will be the LO for a high performance 2meter amateur software defined radio. > (OpenHPSDR.org for info on the SDR) I may multiply it to help with some of > the microwave LOs. It will also use the 20 Mhz to lock a 1GHz TXCO to be > multiplied for microwave LOs. > > Third: I will have three of the LTE-Light units. The first will feed some > LOs as described above, and the synthesized 10 MHz output will be my lab > frequency standard. The lab is in a cinder block room off the basement, with > 2" of foam insulation under 2 inches of concrete which is the floor for a > covered porch above. I'd never thought of it, but the "put it on the floor > next to a brick wall" idea fits here. Actually, I can put it next to 2 > buried brick walls, and will surround it with cinder block on the remaining > sides. Can probably cover it with a few 12x12 paver stones. NOW, this > involves drilling a hole through cinder block and drywall between the > office/ham shack and the lab. Would rather not, but have to anyway. I have > been "informed" that the fan noise from the ham shack gigabit ethernet switch > will become politically unacceptable in about 72 hours. (Office/ham shack > share a guest bedroom.) I would like to get 1E-10 or 1E-11 accuracy out of > this setup. Thanks for this suggestion! > > Fourth: The second unit will be in a building at the base of my antenna > tower, about 350 feet from the house. This building is above ground, and > will be allowed to swing from 45F to 80F over the course of the year. Hence > my interest in insulating and heating. I might consider putting something in > the ground here, the problem would be access for servicing I would like > to get 1E-10 or 1E-11 accuracy out of this unit. Considered shipping 10 MHz > in coax out from the house, would rather not, and would like some redundancy, > anyway. > > Fifth: I get that the /efc/ vs. /temp/ relationship is very complex and > accept that trying to characterize it is not worth the effort. Thanks for > this bit of information. > > Sixth: My third LTE-Lite will drive a 10MHz reference for a mobile ("rover") > microwave setup, providing the reference for a bunch of GHz LOs. This > station will see motion, and temperature variation. Ultra low power will not > be a concern, so heaters are accepta
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Hi guys, this is the kind of lively discussion I was hoping for! I enjoyed this. Some comments (these are my opinions only): * Thanks much for Tom publishing the plots, and spending a lot(!) of time evaluating and helping improve the units significantly. Tom's unit was a pre-production unit. We added RTV (some units black, some a combo) to the TCXO production units based on his suggestion of the successful TP modification. The RTV will help keep airflow away, but additional shielding will help even more. * There is a point where thermally stabilizing the unit does not help anymore. I suspect that point is reached shortly before burying the unit 50 meters underground :) At the point of diminishing marginal returns the GPS and loop noise will be larger than the thermally induced phase offsets. Also local heating from the GPS receiver (which is not constant) will swamp external thermal effects at some point. For us in our lab, the point of diminishing returns is reached when we simply slide the unit into its ESD packaging, then put some pink ESD padding on top of it. With that simple shielding we can get ADEV at 5x to 8x its rated 1ppb performance out of most units. * Temperature changes are typically not the problem with TCXOs, simple airflow and convection turbulence is what causes most of the phase drift problems. As shown by Tom simply putting a layer of TP on top of the unit made a huge difference in stability by keeping convective flow away from the TCXO, while it probably did nothing for temperature insulation. These convective flows are very fast and high-frequency so inside the GPS loop time constant, whereas temp changes are usually easy to low-pass dampen to the point that the GPS loop will hide them. * Actively heating the units' enclosure to some stable temperature is counter-productive in my opinion for two reasons: first higher temperatures cause convective airflow inside the enclosure. We want as little convective flow as possible. Second CMOS slows down at higher temperatures, and noise levels go up with temperature. As mentioned before temperature changes (other than instant changes such as when the sun almost sudden hits the enclosure) usually are easily low-pass filtered to be slower than the GPS loop time constant which is below a couple 100 seconds, so keeping the enclosure at some high temperature is probably going to make things worse. There are other items to consider such as the AT-cut TCXO crystal probably has its most stable operating point at around 25C, and the lifetime MTBF of electronics typically gets cut in half with every 10C Degree increase in temperature. * The 10MHz units have a different RF output than the 20MHz units. The 20MHz units have a 50 Ohms series-terminated and buffered RF output, while the 10MHz units have the TCXO output drive the MMCX connector directly without series impedance matching. Both drive the line with 3.0V CMOS levels. This means the cable on the 10MHz unit should be kept as short as possible, and that impedance matching for maximum power-transfer is not required nor desired. The suggestion that Charles made for checking the impedance by progressively loading the output more and more is valid for Sine Wave outputs, but not for CMOS outputs as implemented on the LTE Lite. One issue is that the TCXO is driving a 1.8V CMOS input through a capacitive voltage divider, and if you load the TCXO so much that its output voltage goes to 1/2 the no-load voltage then the input of the processor will likely not get enough voltage range to operate properly. I mentioned 1M Ohms input impedance simply for convenience as it is a standard input impedance as Charles mentions. You can significantly reduce that impedance since the 10MHz TCXO can drive a handful of mA no problem, and the 20MHz buffered output can drive 20mA or more. This means a 1K Ohms load is also no issue as it would load the output only with 3mA, however(!) the more you load the CMOS output the more heating will happen in the 3.0V linear regulator close to the TCXO and inside the 10MHz DIP-14 TCXO. This will cause load-induced instability. The best input for the LTE-Lite output is simply a 3.3V or 5V powered CMOS gate. No input termination resistance required. Cable lengths should be kept short (less than a foot) to prevent ringing and loading the TCXO output for more than a couple of nanoseconds as the edges traverse into the coax. I like to put a weak pull-down of 470K to 1M on those CMOS gate inputs so the input does not float when its not connected to anything. There is absolutely no need to load down the output with 100 Ohms, 1K, or even 10K. For CMOS inputs, the only thing that makes a difference in phase noise seems to be the rise/fall time and voltage swing. The faster swing and higher voltage the better. Loading down the output will reduce this volt
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
All: I appreciate all the responses to my post earlier today. Very informative. First: DownEast Microwave sells a nice kit for distributing 10 MHz. Specs are on their website, but basically, one in, four out -- each individually buffered and filtered. Second: I will use the 20 MHz from the LTE-Lite to lock a 100Mhz TCXO which will be the LO for a high performance 2meter amateur software defined radio. (OpenHPSDR.org for info on the SDR) I may multiply it to help with some of the microwave LOs. It will also use the 20 Mhz to lock a 1GHz TXCO to be multiplied for microwave LOs. Third: I will have three of the LTE-Light units. The first will feed some LOs as described above, and the synthesized 10 MHz output will be my lab frequency standard. The lab is in a cinder block room off the basement, with 2" of foam insulation under 2 inches of concrete which is the floor for a covered porch above. I'd never thought of it, but the "put it on the floor next to a brick wall" idea fits here. Actually, I can put it next to 2 buried brick walls, and will surround it with cinder block on the remaining sides. Can probably cover it with a few 12x12 paver stones. NOW, this involves drilling a hole through cinder block and drywall between the office/ham shack and the lab. Would rather not, but have to anyway. I have been "informed" that the fan noise from the ham shack gigabit ethernet switch will become politically unacceptable in about 72 hours. (Office/ham shack share a guest bedroom.) I would like to get 1E-10 or 1E-11 accuracy out of this setup. Thanks for this suggestion! Fourth: The second unit will be in a building at the base of my antenna tower, about 350 feet from the house. This building is above ground, and will be allowed to swing from 45F to 80F over the course of the year. Hence my interest in insulating and heating. I might consider putting something in the ground here, the problem would be access for servicing I would like to get 1E-10 or 1E-11 accuracy out of this unit. Considered shipping 10 MHz in coax out from the house, would rather not, and would like some redundancy, anyway. Fifth: I get that the /efc/ vs. /temp/ relationship is very complex and accept that trying to characterize it is not worth the effort. Thanks for this bit of information. Sixth: My third LTE-Lite will drive a 10MHz reference for a mobile ("rover") microwave setup, providing the reference for a bunch of GHz LOs. This station will see motion, and temperature variation. Ultra low power will not be a concern, so heaters are acceptable. I would be happy with 1E-9 accuracy out of this unit. That translates into 10Hz frequency error at 10 GHz. This kind of frequency accuracy has been demonstrated to provide 3+db improvement in the ability to detect weak signals -- very significant for microwave weak signal work. Finally: I have pondered all the suggestions about measuring output impedance, etc. For now, I have decided to default to Said's expertise with the units and will use one of his suggested circuits as buffers. Hopefully, these will be on a board inside the HAMMOND box with the LTE-Lite. That buffer will drive one of the MMICs to provide additional power to drive a filter and then output to the distribution amplifier. I will continue to look for a better idea from one of you smarter than me. Thanks again for all the insight and ideas. You guys type and I learn. 73, Jim wb4...@amsat.org On 11/23/2014 4:46 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: I would like to make a unit with multiple 10 MHz 50 Ohm outputs to feed my various bits of test equipment. I am thinking about some practical considerations. 1) It would be great if there was a circuit published which can give 50 Ohn output impedance from a 12-15 power supply, which a) Doesn't load the TCXO b) Doesn't degrade the phase noise. c) Powered the LTE lite. Ideally one for both 10 & 20 MHz crystals. Better still if there was a PCB available. 2) How should I mount the components? My preference would be a metal box with * IEC mains socket * antenna input socket * 9-pin D for reading dats * 15 BNC's outputs With a power amplifier to provide the output for 15 sockets, some ventilation possibly requiring a small amount of forced air cooling would be needed. But given the TCXO"s sensitivity to temperature changes, I don't know whether it might be preferable to mount the LTE lite in its own box without any power supplies in it - perhaps with some thermally insulting material around the LTE lite so the crystal doesn't experience any fast temperature changes. Then have the power hungry bits completely separately. I don't have a particularly big lab, so wherever I mount the LTE lite, the temperature is going to change with the air conditioning unit blows hot or cold There are fairly large temperature changes when I am not using the lab, as I don't run the air condition
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Did you use one-ply, two-ply, or three-ply TP? More seriously, your LTE-Lite differs in a couple of respects from the batch of "production" ones, or at least my example. Your TCXO seems to be in a metal package (shiny gold colour) and open to the air, if I'm interpreting the photo on your LTE-Lite page correctly (and also the photo that Said posted in his divide-by-two document). The production units have the TCXO in a solid black package, probably black epoxy, with a blob of RTV rubber on top. So the "production" units are probably already somewhat better shielded against drafts. (Thanks for doing the tests, particularly for those of us who can't do these tests ourselves. I can only watch the 1 PPS of the LTE-Lite wander with respect to the 1 PPS from my old Thunderbolt (Piezo oscillator), and look at the worst-case variation, but I have no way of knowing how much of the drift is due to each GPSDO). - Dave On Sun, Nov 23, 2014 at 11:24 AM, Tom Van Baak wrote: > The short-term performance is 10x worse if you don't shield the TCXO from > air, even if the ambient air is "still". I suggested Said sell the product > with some sort of engineered shield in place. Instead each of us will solve > the problem in our own way; which is ok for a dev kit. > > For plots and photos showing performance with, and without, and with > insulation see: > http://leapsecond.com/pages/LTE-Lite/ > The difference is dramatic, especially if you are used to working with > OCXO where this sort of effect does not occur. > > The insulation may be found in convenient rolls at many local stores. I > used TP, which for this application is an acronym for Thermal Paper. > > /tvb > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Interesting comment about the geothermal. I have to take continuing education courses in order to maintain my PE; one was in geothermal. Intuitively, great for cooling, even (especially!) in Florida. Intuitively, not so hot for heating, especially in PA, and especially with the price of natural gas plummeting. The guy who services our conventional AC and gas furnace was not very enthused, when I told him I was considering geothermal for the next cooling unit. He got a little more enthused when he found out I already have more pipe in the ground than I'd need (ft per ton of cooling capacity) and a several thousand gallon in-ground tank. Still not excited about it. I really appreciate your new data point. Shortly, I'll post response to all replies to my original post on this topic. For now, the bury it option might actually have use here. Jim On 11/23/2014 11:46 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: On 23 Nov 2014 14:45, "Bob Camp" wrote: Hi If you have a basement in your house / building I do not. —and — it’s dry and reasonably draft free (no garage doors opening up from time to time) My lab is a room which is part of the garage! Just about everything is against me with this method, BUT you do give me an idea... You got me thinking about the possibility of actually mounting the TCXO burried in the ground! The temperature of that is not going to change very rapidly. FWIW, I know a guy that did work as an air conditioning engineer,, but now works for a company selling geothermal heating. He installs ground source heat pumps for the geothermal energy. He says that they actually work quite poorly in many cases. In a couple of years the temperature of the ground falls as the heat is extracted faster than it replenishes. So the efficiency falls off. I don't think that the TCXO would heat the ground faster than it dissipates away. Of course there would be some practical issues burying the TCXO, but those would not be insurmountable ones. I have no idea what depth might be needed. My wife thinks thinks I am a nutcase - that would only confirm it to her! Dave, G8WRB ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
I've read about die-hard microwave hams burying their master oscillators for a long time . . . . On 11/23/2014 11:46 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: On 23 Nov 2014 14:45, "Bob Camp" wrote: Hi If you have a basement in your house / building I do not. —and — it’s dry and reasonably draft free (no garage doors opening up from time to time) My lab is a room which is part of the garage! Just about everything is against me with this method, BUT you do give me an idea... You got me thinking about the possibility of actually mounting the TCXO burried in the ground! The temperature of that is not going to change very rapidly. FWIW, I know a guy that did work as an air conditioning engineer,, but now works for a company selling geothermal heating. He installs ground source heat pumps for the geothermal energy. He says that they actually work quite poorly in many cases. In a couple of years the temperature of the ground falls as the heat is extracted faster than it replenishes. So the efficiency falls off. I don't think that the TCXO would heat the ground faster than it dissipates away. Of course there would be some practical issues burying the TCXO, but those would not be insurmountable ones. I have no idea what depth might be needed. My wife thinks thinks I am a nutcase - that would only confirm it to her! Dave, G8WRB ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Schomandl -- the company which made the first indirect synthesizers in the sixties in the past century -- used buried crystal oscillators as standard frequency source, 12meter deep in the companies yard in the Belfort Strasse in Munich, Bavaria Germany, ...Rohde& Schwarz also had buried oscillators. I have one in California, where, the temperature at 10m deep is 15,784C° around the year, and measuring the frequency off set between wwvb's harmonic and the buried oscillator originally tuned to cca 3MHz, to the natural serial resonance of the crystal, by counting the beat -- to a harmonic of wwvb, cca 4217Hz , 364 358 801 pulses per day, as of Nov 2014, counter resets by wwvb daily, daily changes max ± 8 pulses, are to see, but a yearly decrement of 15 to 8 pulses per year, less per year in the last time is observable the "system down there"is running since 1991. 73 KJ6UHN Alex On 11/23/2014 8:46 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: On 23 Nov 2014 14:45, "Bob Camp" wrote: Hi If you have a basement in your house / building I do not. —and — it’s dry and reasonably draft free (no garage doors opening up from time to time) My lab is a room which is part of the garage! Just about everything is against me with this method, BUT you do give me an idea... You got me thinking about the possibility of actually mounting the TCXO burried in the ground! The temperature of that is not going to change very rapidly. FWIW, I know a guy that did work as an air conditioning engineer,, but now works for a company selling geothermal heating. He installs ground source heat pumps for the geothermal energy. He says that they actually work quite poorly in many cases. In a couple of years the temperature of the ground falls as the heat is extracted faster than it replenishes. So the efficiency falls off. I don't think that the TCXO would heat the ground faster than it dissipates away. Of course there would be some practical issues burying the TCXO, but those would not be insurmountable ones. I have no idea what depth might be needed. My wife thinks thinks I am a nutcase - that would only confirm it to her! Dave, G8WRB ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
In message , "Dr. David Kirkby (Kirkby Microwave Ltd)" writes: >> Geothermal means you drill at least 50m (Iceland) or more likely >> half a kilometer down, in order to harvest water at near boiling >> point from the Earths geological heat-sources (mostly uranium decay). > >Sorry. What he installs is pipes in the ground in residential or >industrial sites. Basically he says they work initially, but performance >drops dramatically over a couple of years. That is not "geothermal" then, and yes, a LOT of those systems are badly underdimensioned. I've been researching this topic intensively because my new house will be heated that way. My conclusion, based on reading a lot of reports, is that there is no credible way to predict the performance. The wetter your soil the better, but that's about it. I'm going to overprovision by a factor two to be on the safe side, afterall it only costs EUR7 for each extra meter of pipe. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
On 23 Nov 2014 17:49, "Poul-Henning Kamp" wrote: > > > In message < canx10hb0kdrnaayzgvm1gkduj7gklth0acdxczg894hxbus...@mail.gmail.com> > , "Dr. David Kirkby (Kirkby Microwave Ltd)" writes: > > >He installs ground source > >heat pumps for the geothermal energy. He says that they actually work > >quite poorly in many cases. > > There is a BIG difference between geothermal and ground heating. > > Geothermal means you drill at least 50m (Iceland) or more likely > half a kilometer down, in order to harvest water at near boiling > point from the Earths geological heat-sources (mostly uranium decay). Sorry. What he installs is pipes in the ground in residential or industrial sites. Basically he says they work initially, but performance drops dramatically over a couple of years. > If you extract more energy than you deposit sunshine, you end > up freezing a larger and larger volume of water/soil around > the pipe and your compressor will eat a lot of electricity. That is what he was saying. Dave. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
In message , "Dr. David Kirkby (Kirkby Microwave Ltd)" writes: >He installs ground source >heat pumps for the geothermal energy. He says that they actually work >quite poorly in many cases. There is a BIG difference between geothermal and ground heating. Geothermal means you drill at least 50m (Iceland) or more likely half a kilometer down, in order to harvest water at near boiling point from the Earths geological heat-sources (mostly uranium decay). Extracting more energy than available just means the temperature drops temporarily. It will increase again once you reduce the pump rate. Horizontal ground heat means that you are harvesting sunshine accumulated in the top one meter of the soil. Much of the energy is harvested from freezing the water around the pipe thus pulling out the relatively high melting energy of water. If you extract more energy than you deposit sunshine, you end up freezing a larger and larger volume of water/soil around the pipe and your compressor will eat a lot of electricity. In practice it looks like this: http://ing.dk/artikel/varmepumpe-mareridt-jordslange-var-dybfrossen-i-maj-113176 (The two pictures show the same pipe, with and without frozen ground.) Finally there is vertial ground heat where you drill down only about 40-80 meter, tapping heat mostly from ground water resources.Most places the ground water doesn't move fast enough to deliver the amounts of energy extracted, and over time the source returns unusably low temperature and must be abandonned. Typically after 25-30 years. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
On 23 Nov 2014 14:45, "Bob Camp" wrote: > > Hi > > If you have a basement in your house / building I do not. > —and — > it’s dry and reasonably draft free (no garage doors opening up from time to time) My lab is a room which is part of the garage! Just about everything is against me with this method, BUT you do give me an idea... You got me thinking about the possibility of actually mounting the TCXO burried in the ground! The temperature of that is not going to change very rapidly. FWIW, I know a guy that did work as an air conditioning engineer,, but now works for a company selling geothermal heating. He installs ground source heat pumps for the geothermal energy. He says that they actually work quite poorly in many cases. In a couple of years the temperature of the ground falls as the heat is extracted faster than it replenishes. So the efficiency falls off. I don't think that the TCXO would heat the ground faster than it dissipates away. Of course there would be some practical issues burying the TCXO, but those would not be insurmountable ones. I have no idea what depth might be needed. My wife thinks thinks I am a nutcase - that would only confirm it to her! Dave, G8WRB ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
The short-term performance is 10x worse if you don't shield the TCXO from air, even if the ambient air is "still". I suggested Said sell the product with some sort of engineered shield in place. Instead each of us will solve the problem in our own way; which is ok for a dev kit. For plots and photos showing performance with, and without, and with insulation see: http://leapsecond.com/pages/LTE-Lite/ The difference is dramatic, especially if you are used to working with OCXO where this sort of effect does not occur. The insulation may be found in convenient rolls at many local stores. I used TP, which for this application is an acronym for Thermal Paper. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Poul-Henning wrote: Charles' design works great from the outside, but doesn't do anything with respect to the thermal energy expended by the encapsulated device themselves, which will cause convection in the inner box. I have been using the technique for 30+ years, including with many OCXOs (which, obviously, generate significant heat) and have never observed any problems of that nature at the 1e-13 level. I did consider the possibility when I first started doing it, and tested two potential fixes: (i) putting a fan inside the box to homogenize the internal temperature, and (ii) filling the air space inside the box with irregular solid shapes to break up the convection pattern. I tested both methods extensively with instrumented sources, in many variations (fan speeds and orientations, mass and porosity of passive internal shapes), and did not find any difference at the 1e-13 level. I have occasionally used an internal fan just on theoretical grounds, but I have never measured any practical difference. Thinking about it, this does not seem too surprising -- one would expect any convection to settle into a stable pattern and thus not to cause any temperature changes over time (once it is warm and settled). Whether this explains my results or some other effect predominates (for example, convection may move enough air in the limited space to achieve substantial isothermy), I have confirmed to my satisfaction that it is simply not a factor in practice at the levels we are concerned with. If you test the "cast aluminum box" method and find that your results do not accord with mine, please publish them and we can discuss what might account for the observed differences and how the method could be improved. Until then, you are just posting speculative musings on the subject based on no data, which does not seem helpful. And good luck fitting a cubic foot box with a surround of bricks into a 3U rack cabinet, or any other relocatable (much less, semi-portable) enclosure. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Hi Yup, that’s another good reason for the plastic bag :) If moisture might be an issue in your area, cover up the corner for a while in the rainy season to check for that problem before the project begins. Depending on the bag is not a real good idea. Bob > On Nov 23, 2014, at 9:50 AM, Poul-Henning Kamp wrote: > > > In message , Bob Camp writes: > >> At least one side / corner is well buried in the ground > > But be aware that such a corner may be dry only when empty. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
I am scratching my head here. >From what I see the LTE is a good unit but does swim around a bit. The conclusion I might get from this thread is that lots of insulation will fix that. I suspect not. The LTE in use down at 2.8 e-10 according to its output. I have put it in a small cardboard box with free standing air and some Styrofoam. Because thats what turned up in the basement. I have added heat to it. It sits on top the Lucent box thats on. :-) It still swims around. It moves forward and backwards stays steady. Random. Certainly not terrible. I just think as neat as bricks may be it would not help allot. The top of the thread is excellant about checking the TCXO output Z. Regards Paul WB8TSL On Sun, Nov 23, 2014 at 9:55 AM, Poul-Henning Kamp wrote: > > In message <20141123174632.kvk4s...@smtp18.mail.yandex.net>, Charles > Steinmetz > writes: > > >And good luck fitting a cubic foot box with a surround of bricks into > >a 3U rack cabinet, or any other relocatable (much less,semi-portable) > >enclosure. > > I didn't say it doesn't work, I said that I don't agree with it ;-) > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Hi What you have in the LTE is a TCXO rather than a bare crystal or an OCXO. It’s got a compensation circuit that corrects the FT curve of the crystal. The net result is likely a 5th or higher order curve when you plot frequency over temperature. Every TCXO off that production line will have a different curve. You would need a full characterization of that curve for your specific TCXO to pick an optimum point. With a GPSDO, taking care of the long term drift is not what you are after. The GPS does that. If the GPSDO is TCXO based, the the loop filter is going to be pretty fast. That is *not* a knock on the LTE part, it’s just physics. An OCXO part is a different beast. Each has their strong points. Don’t try to run the OCXO off batteries for a week … With a fast filter, temperature variations at the “per hour” level are not likely an issue. Once you get to the point that drafts are worked out, and that temperature change is slowed down, you are done. No need for anything more complex. Bob > On Nov 23, 2014, at 9:30 AM, Jim Sanford wrote: > > All: > I am enjoying this thread. These are all very interesting ideas. > > Hoping to power up my first unit later today > > I'm putting my LTE-Lite in the recommended HAMMOND box. That takes care of > the box with air. I was then considering proportional heating of the surface > of the box, like I did long ago with some GUNNPLEXERS -- seemed to work > pretty well. Then this whole assembly goes inside two or four inches of the > foam insulation. > > Now, the question becomes, to what temperature to heat it? With a crystal, > I'd plot /f/ vs. /T/, and look for minimum slope. How to do that with > LTE-Lite -- plot /efc/ vs /T/ and look for either center of range or minimum > slope?? > > Thoughts? > > Jim > wb4...@amsat.org > > On 11/23/2014 9:03 AM, Magnus Danielson wrote: >> NIST did something similar for their WWWV site, where they used bottled >> water in its staple packaging to build a thermal mass. They measured how >> their atomic clocks and rig behaved before and after, and could see the >> difference. Very neat way of using off the (store)shelf components for a >> test. >> >> Another aspect is to think about what kind of heating/coolling you have. If >> it can act more as a proportional system rather than bang-bang regulations, >> it won't produce as drastic swings for you. >> >> Cheers, >> Magnus >> >> On 11/23/2014 02:32 PM, Poul-Henning Kamp wrote: >>> >>> In message <20141123153744.biokf...@smtp16.mail.yandex.net>, Charles >>> Steinmetz >>> writes: >>> First, mount the LTE in a cast aluminum box (not thin sheet metal, something with some heft). [...] >>> >>> Charles' design has some good points, but I don't agree with it. >>> >>> What you are trying to do is to low-pass filter any thermal signals >>> before they reach the LTE or OCXO. >>> >>> Charles' design works great from the outside, but doesn't do anything >>> with respect to the thermal energy expended by the encapsulated >>> device themselves, which will cause convection in the inner box. >>> >>> (For LTE and OCXO it is probably less of a problem that changing >>> power-disipation will have a outsized effect on the central >>> temperature.) >>> >>> Here is a much simpler and likely cheaper way to do it: >>> >>> Put the LTE or OCXO in a small box of your choice. Even a cardboard >>> box is fine. A little thermal insulation in the box is OK, but not >>> too much, the heat must be able to get out. >>> >>> Find a medium sized cardboard box, something like a cubic feet or so. >>> >>> Place it where you want your house-standard, with some kind of >>> thermal insulation under it, two layers of old rug will do fine. >>> >>> Lay a floor of bricks inside the box. >>> >>> Build a "wall" of bricks along the outside of the box. >>> >>> Place the smaller box in the hole in the middle, cut the >>> corner of a brick to run the cables without too much leakage. >>> >>> Use a floortile as roof, possibly with a layer of bricks on top. >>> >>> Close the outher cardboard box with tape to minimize convection. >>> >>> Congratulations, you now have a cheap and incredibly efficient >>> thermal low-pas filter, which will allow thermal energy to move in >>> both directions -- eventually. >>> >>> The outher cardboard box is not optional, unless you replace it >>> with some other "mostly air-tight" barrier. >>> >>> The little bit of insulation the outher cardboard adds are not a >>> bad idea either, for instance it reduces the effect of sunlight >>> hits the box at certain times of the day/year. >>> >>> But you can substitute any geological building material you have >>> at hand for the bricks, because the trick is that geological building >>> materials have just the right thermal properties we are looking >>> for: Decent but not too good thermal conductivity with healthy >>> dose of thermal mass. >>> >>> Cinderblocks comes with convenient
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
In message <20141123174632.kvk4s...@smtp18.mail.yandex.net>, Charles Steinmetz writes: >And good luck fitting a cubic foot box with a surround of bricks into >a 3U rack cabinet, or any other relocatable (much less,semi-portable) >enclosure. I didn't say it doesn't work, I said that I don't agree with it ;-) -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
In message , Bob Camp writes: >At least one side / corner is well buried in the ground But be aware that such a corner may be dry only when empty. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Hi If you have a basement in your house / building —and — it’s dry and reasonably draft free (no garage doors opening up from time to time) — and — At least one side / corner is well buried in the ground — and — You can get at that corner / side. Move your thermal baffle gizmo up against that wall, move it into that corner. There is a lot more mass in the foundation of a building than anything you would want to lug around for a project. You still need to handle the issues on at least half the surface, that should be less trouble than doing the whole thing. There is another subtle advantage to this approach. The standard is out of the way. It’s not in the middle of the lab. It does not get bumped. It does not get sparked (unless you have full ESD protection in the lab …). It’s less likely to have random power cycle events due to cords being accidentally pulled. Even second order stuff related to ground loops from connecting and disconnecting cables may be reduced. “Just leave it alone” is much easier to do when the gizmo is surrounded by a pile of bricks. With a GPSDO, you don’t care (much) about the environmental swings from week to week or month to month. The GPS will take care of that. What you care about are the hour to hour or minute to minute movements. Those are the ones that the filter on an OCXO based unit will struggle with. Hotter in the summer / colder in the winter is not as big a deal as “cold when I come in / hot after I turn everything on”. One practical hint if you do try this: Put a cheap plastic bag around the gizmo and tape it up. It discourages the bug colonies. I have empirical evidence that this is a good idea ... Bob > On Nov 23, 2014, at 9:03 AM, Magnus Danielson > wrote: > > NIST did something similar for their WWWV site, where they used bottled water > in its staple packaging to build a thermal mass. They measured how their > atomic clocks and rig behaved before and after, and could see the difference. > Very neat way of using off the (store)shelf components for a test. > > Another aspect is to think about what kind of heating/coolling you have. If > it can act more as a proportional system rather than bang-bang regulations, > it won't produce as drastic swings for you. > > Cheers, > Magnus > > On 11/23/2014 02:32 PM, Poul-Henning Kamp wrote: >> >> In message <20141123153744.biokf...@smtp16.mail.yandex.net>, Charles >> Steinmetz >> writes: >> >>> First, mount the LTE in a cast aluminum box (not thin sheet metal, >>> something with some heft). [...] >> >> Charles' design has some good points, but I don't agree with it. >> >> What you are trying to do is to low-pass filter any thermal signals >> before they reach the LTE or OCXO. >> >> Charles' design works great from the outside, but doesn't do anything >> with respect to the thermal energy expended by the encapsulated >> device themselves, which will cause convection in the inner box. >> >> (For LTE and OCXO it is probably less of a problem that changing >> power-disipation will have a outsized effect on the central >> temperature.) >> >> Here is a much simpler and likely cheaper way to do it: >> >> Put the LTE or OCXO in a small box of your choice. Even a cardboard >> box is fine. A little thermal insulation in the box is OK, but not >> too much, the heat must be able to get out. >> >> Find a medium sized cardboard box, something like a cubic feet or so. >> >> Place it where you want your house-standard, with some kind of >> thermal insulation under it, two layers of old rug will do fine. >> >> Lay a floor of bricks inside the box. >> >> Build a "wall" of bricks along the outside of the box. >> >> Place the smaller box in the hole in the middle, cut the >> corner of a brick to run the cables without too much leakage. >> >> Use a floortile as roof, possibly with a layer of bricks on top. >> >> Close the outher cardboard box with tape to minimize convection. >> >> Congratulations, you now have a cheap and incredibly efficient >> thermal low-pas filter, which will allow thermal energy to move in >> both directions -- eventually. >> >> The outher cardboard box is not optional, unless you replace it >> with some other "mostly air-tight" barrier. >> >> The little bit of insulation the outher cardboard adds are not a >> bad idea either, for instance it reduces the effect of sunlight >> hits the box at certain times of the day/year. >> >> But you can substitute any geological building material you have >> at hand for the bricks, because the trick is that geological building >> materials have just the right thermal properties we are looking >> for: Decent but not too good thermal conductivity with healthy >> dose of thermal mass. >> >> Cinderblocks comes with convenient interior holes premade. >> >> Aerated concrete blocks are also a candidate material but >> don't make it too thick since it insulates quite well, and >> paint the surface to bind the dust.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Dave wrote: It would be great if there was a circuit published which can give 50 Ohn output impedance from a 12-15 power supply, which a) Doesn't load the TCXO b) Doesn't degrade the phase noise. WRT loading the TCXO, someone should establish quantitatively how high the load impedance must be to avoid significant negative effects. Said mentioned 1M ohm, which is the "other" common lab instrument input impedance besides 50 ohms, but I would be very surprised to find that the load resistance really needs to be that high. Why does this matter? The lower the impedance you load the oscillator with, the more power you get out of it; therefore, the lower the power gain that is necessary to develop an output signal you can use to feed the external world -- and, consequently, the less noise you are forced to add to the signal during amplification. I would recommend testing the LTE with a 1M ohm load resistance to establish a baseline. 1) Measure and record the outout voltage. 2) Measure and record the levels of the first few harmonics in relation to the carrier. 3) Get a qualitative feel for the levels of higher harmonics. Then, start reducing the load impedance (I would start with 10k ohms, then move to 1k ohms), paying attention to: a) The output voltage b) The levels of the first few harmonics in relation to the carrier, and c) The levels of higher harmonics, if they increase faster than the first few as the load resistance decreases. When you get to the point where the output voltage drops to 1/2 of the 1M ohm voltage, you have reached the output impedance of the LTE board (matched source and load impedances). As a general matter, it would not be useful to use a load impedance lower than this. If you reach this point without a significant increase in the output harmonics, great -- use this impedance as the input resistance of your buffer amplifier. If, however, the harmonics increase faster (with decreasing load resistance) and become objectionable before you reach the 1/2 voltage point, you must decide how much distortion is acceptable and use the load resistance that produces this level of harmonics. In this case, you trade off distortion and noise. So, the first step is for someone to do the experiment and find out how low the input resistance of the buffer amp can be as a practical matter. Then, a buffer amp topology can be chosen for best performance with this input resistance. Also, determine how many oscillator-frequency outputs you need (including outputs that will feed dividers, multipliers, or other circuitry internal to the buffer box). This will also influence the optimum choice of buffer amp topology. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
All: I am enjoying this thread. These are all very interesting ideas. Hoping to power up my first unit later today I'm putting my LTE-Lite in the recommended HAMMOND box. That takes care of the box with air. I was then considering proportional heating of the surface of the box, like I did long ago with some GUNNPLEXERS -- seemed to work pretty well. Then this whole assembly goes inside two or four inches of the foam insulation. Now, the question becomes, to what temperature to heat it? With a crystal, I'd plot /f/ vs. /T/, and look for minimum slope. How to do that with LTE-Lite -- plot /efc/ vs /T/ and look for either center of range or minimum slope?? Thoughts? Jim wb4...@amsat.org On 11/23/2014 9:03 AM, Magnus Danielson wrote: NIST did something similar for their WWWV site, where they used bottled water in its staple packaging to build a thermal mass. They measured how their atomic clocks and rig behaved before and after, and could see the difference. Very neat way of using off the (store)shelf components for a test. Another aspect is to think about what kind of heating/coolling you have. If it can act more as a proportional system rather than bang-bang regulations, it won't produce as drastic swings for you. Cheers, Magnus On 11/23/2014 02:32 PM, Poul-Henning Kamp wrote: In message <20141123153744.biokf...@smtp16.mail.yandex.net>, Charles Steinmetz writes: First, mount the LTE in a cast aluminum box (not thin sheet metal, something with some heft). [...] Charles' design has some good points, but I don't agree with it. What you are trying to do is to low-pass filter any thermal signals before they reach the LTE or OCXO. Charles' design works great from the outside, but doesn't do anything with respect to the thermal energy expended by the encapsulated device themselves, which will cause convection in the inner box. (For LTE and OCXO it is probably less of a problem that changing power-disipation will have a outsized effect on the central temperature.) Here is a much simpler and likely cheaper way to do it: Put the LTE or OCXO in a small box of your choice. Even a cardboard box is fine. A little thermal insulation in the box is OK, but not too much, the heat must be able to get out. Find a medium sized cardboard box, something like a cubic feet or so. Place it where you want your house-standard, with some kind of thermal insulation under it, two layers of old rug will do fine. Lay a floor of bricks inside the box. Build a "wall" of bricks along the outside of the box. Place the smaller box in the hole in the middle, cut the corner of a brick to run the cables without too much leakage. Use a floortile as roof, possibly with a layer of bricks on top. Close the outher cardboard box with tape to minimize convection. Congratulations, you now have a cheap and incredibly efficient thermal low-pas filter, which will allow thermal energy to move in both directions -- eventually. The outher cardboard box is not optional, unless you replace it with some other "mostly air-tight" barrier. The little bit of insulation the outher cardboard adds are not a bad idea either, for instance it reduces the effect of sunlight hits the box at certain times of the day/year. But you can substitute any geological building material you have at hand for the bricks, because the trick is that geological building materials have just the right thermal properties we are looking for: Decent but not too good thermal conductivity with healthy dose of thermal mass. Cinderblocks comes with convenient interior holes premade. Aerated concrete blocks are also a candidate material but don't make it too thick since it insulates quite well, and paint the surface to bind the dust. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
NIST did something similar for their WWWV site, where they used bottled water in its staple packaging to build a thermal mass. They measured how their atomic clocks and rig behaved before and after, and could see the difference. Very neat way of using off the (store)shelf components for a test. Another aspect is to think about what kind of heating/coolling you have. If it can act more as a proportional system rather than bang-bang regulations, it won't produce as drastic swings for you. Cheers, Magnus On 11/23/2014 02:32 PM, Poul-Henning Kamp wrote: In message <20141123153744.biokf...@smtp16.mail.yandex.net>, Charles Steinmetz writes: First, mount the LTE in a cast aluminum box (not thin sheet metal, something with some heft). [...] Charles' design has some good points, but I don't agree with it. What you are trying to do is to low-pass filter any thermal signals before they reach the LTE or OCXO. Charles' design works great from the outside, but doesn't do anything with respect to the thermal energy expended by the encapsulated device themselves, which will cause convection in the inner box. (For LTE and OCXO it is probably less of a problem that changing power-disipation will have a outsized effect on the central temperature.) Here is a much simpler and likely cheaper way to do it: Put the LTE or OCXO in a small box of your choice. Even a cardboard box is fine. A little thermal insulation in the box is OK, but not too much, the heat must be able to get out. Find a medium sized cardboard box, something like a cubic feet or so. Place it where you want your house-standard, with some kind of thermal insulation under it, two layers of old rug will do fine. Lay a floor of bricks inside the box. Build a "wall" of bricks along the outside of the box. Place the smaller box in the hole in the middle, cut the corner of a brick to run the cables without too much leakage. Use a floortile as roof, possibly with a layer of bricks on top. Close the outher cardboard box with tape to minimize convection. Congratulations, you now have a cheap and incredibly efficient thermal low-pas filter, which will allow thermal energy to move in both directions -- eventually. The outher cardboard box is not optional, unless you replace it with some other "mostly air-tight" barrier. The little bit of insulation the outher cardboard adds are not a bad idea either, for instance it reduces the effect of sunlight hits the box at certain times of the day/year. But you can substitute any geological building material you have at hand for the bricks, because the trick is that geological building materials have just the right thermal properties we are looking for: Decent but not too good thermal conductivity with healthy dose of thermal mass. Cinderblocks comes with convenient interior holes premade. Aerated concrete blocks are also a candidate material but don't make it too thick since it insulates quite well, and paint the surface to bind the dust. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
Dave wrote But given the TCXO"s sensitivity to temperature changes, I don't know whether it might be preferable to mount the LTE lite in its own box without any power supplies in it - perhaps with some thermally insulting material around the LTE lite so the crystal doesn't experience any fast temperature changes. First, mount the LTE in a cast aluminum box (not thin sheet metal, something with some heft). Use thermally insulating standoffs (teflon or nylon, with no metal "through" fasteners) to get the board in the middle of the volume of the box. Use a box a bit larger than you'd first think, so there is at least 1" of air on all 6 sides of the LTE board. Do NOT mount any part of the LTE board (connectors, etc.) directly to the box walls -- use "pigtails" for all connections. Do NOT use any insulation between the LTE and the box walls other than the 1"+ of air. The mounting described above will add substantial thermal capacitance to the LTE board (good) without adding significant thermal resistance (bad). For further discussions of this issue, search the list archives for "thermal capacitance" and "thermal mass." Now, mount the cast box (plus any thermal mass you add to it -- see below) so that IT is thermally isolated from the overall enclosure (or, if it sits out in the open, thermally isolated from anything solid). The air space in the enclosure isolates the oscillator from the cast box and the box is sufficiently massive that its temperature cannot change nearly as fast as ambient. The thermal mass of the cast box can be adjusted by adding thermal mass to it as desired. The goal is for the box temperature to change only by changes in ambient AIR temperature, and the LTE board to change only by changes in the AIR temperature inside the cast box. This integrates any changes to the LTE board temperature with a very long time constant, which allows the GPS discipline to track and cancel the temperature changes. (If you mount an ovenized oscillator this same way, it integrates any changes to the OCXO temperature so that the oven control loop can track and cancel any changes to the crystal temperature.) You can, of course, improve things even further by making sure the ambient air temperature surrounding the cast box changes slowly, or not at all. But the technique described above can be counted on to reduce thermal effects in most OCXOs or GPSDOs to better (often much better) than the 1e-13 level unless the ambient temperature changes MUCH more and MUCH faster than any change we wouild consider normal for a living space. This is true whether the cast box is mounted out in the open, or inside an overall enclosure with other electronics. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Practical considerations making a lab standard with an LTE lite
In message <20141123153744.biokf...@smtp16.mail.yandex.net>, Charles Steinmetz writes: >First, mount the LTE in a cast aluminum box (not thin sheet metal, >something with some heft). [...] Charles' design has some good points, but I don't agree with it. What you are trying to do is to low-pass filter any thermal signals before they reach the LTE or OCXO. Charles' design works great from the outside, but doesn't do anything with respect to the thermal energy expended by the encapsulated device themselves, which will cause convection in the inner box. (For LTE and OCXO it is probably less of a problem that changing power-disipation will have a outsized effect on the central temperature.) Here is a much simpler and likely cheaper way to do it: Put the LTE or OCXO in a small box of your choice. Even a cardboard box is fine. A little thermal insulation in the box is OK, but not too much, the heat must be able to get out. Find a medium sized cardboard box, something like a cubic feet or so. Place it where you want your house-standard, with some kind of thermal insulation under it, two layers of old rug will do fine. Lay a floor of bricks inside the box. Build a "wall" of bricks along the outside of the box. Place the smaller box in the hole in the middle, cut the corner of a brick to run the cables without too much leakage. Use a floortile as roof, possibly with a layer of bricks on top. Close the outher cardboard box with tape to minimize convection. Congratulations, you now have a cheap and incredibly efficient thermal low-pas filter, which will allow thermal energy to move in both directions -- eventually. The outher cardboard box is not optional, unless you replace it with some other "mostly air-tight" barrier. The little bit of insulation the outher cardboard adds are not a bad idea either, for instance it reduces the effect of sunlight hits the box at certain times of the day/year. But you can substitute any geological building material you have at hand for the bricks, because the trick is that geological building materials have just the right thermal properties we are looking for: Decent but not too good thermal conductivity with healthy dose of thermal mass. Cinderblocks comes with convenient interior holes premade. Aerated concrete blocks are also a candidate material but don't make it too thick since it insulates quite well, and paint the surface to bind the dust. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Practical considerations making a lab standard with an LTE lite
I would like to make a unit with multiple 10 MHz 50 Ohm outputs to feed my various bits of test equipment. I am thinking about some practical considerations. 1) It would be great if there was a circuit published which can give 50 Ohn output impedance from a 12-15 power supply, which a) Doesn't load the TCXO b) Doesn't degrade the phase noise. c) Powered the LTE lite. Ideally one for both 10 & 20 MHz crystals. Better still if there was a PCB available. 2) How should I mount the components? My preference would be a metal box with * IEC mains socket * antenna input socket * 9-pin D for reading dats * 15 BNC's outputs With a power amplifier to provide the output for 15 sockets, some ventilation possibly requiring a small amount of forced air cooling would be needed. But given the TCXO"s sensitivity to temperature changes, I don't know whether it might be preferable to mount the LTE lite in its own box without any power supplies in it - perhaps with some thermally insulting material around the LTE lite so the crystal doesn't experience any fast temperature changes. Then have the power hungry bits completely separately. I don't have a particularly big lab, so wherever I mount the LTE lite, the temperature is going to change with the air conditioning unit blows hot or cold There are fairly large temperature changes when I am not using the lab, as I don't run the air conditioning unit 24/7. I am interested in people's thoughts on the best way to go about this. For testing I have a couple of signal generators that have ovens that are powered 24/7. Also I should soon have the SR620. Dave. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.