Re: [time-nuts] Spectrum Analyzer Specifications --> phase noise test set
On 03/25/2016 05:55 PM, Bruce Griffiths wrote: As long as BNC connectors are avoided as their phase shift isnt that stable.. A small mechanical disturbance will change it significantly. Actually low noise PN measurement systems can be very sensitive to cable movement. Bolting modules to a metal baseplate helps a lot as does using intermodule connections comprising SMA(m)-SMA(m) barrels rather than cables. There's also the question of mixer port termination.The nist paper by Walls and Stein indicates that capacitive termination of the IF port may be effective in reducing noise whilst maintaining a flat response fro dc to around 50KHz.Small value resistors in series with the RF and LO ports are then useful in reducing the VSWR. I replaced the faulty attenuator in one of my HP 8648 signal generators. The "plumbing" in them is fascinating and instructive, rigid metal tubes with smooth, continuous bends rather than flexible coaxial cable, and mating with SMA connectors on both ends. My 8468C is good from 9 kHz to 3200 MHz, and where my 8568B only went to 1.5 GHz, I was able to test the 8468C with the least spec. Signal Hound, SA44B, that goes to 4.4 GHz. Ian, G4ICV, AB2GR -- ___ 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] Spectrum Analyzer Specifications --> phase noise test set
Use TNC, which is free of the problem and it fits into the same hole... 73 KJ6UHN Alex On 3/25/2016 3:46 PM, Bob Camp wrote: Hi The sensitivity of BNC connectors goes up quite a bit as they wear out. Both sides of the connection are subject to wear. Replacing both sides is often the only solution when they get noisy. That said, “screw down” connectors are a better way to go. The “capacitive loading” termination of the mixer is something that a number of us tried to reproduce when the paper came out. Even after fairly extensive conversations with the authors, the effect seems be quite difficult to reproduce. It certainly is not a “general solution” to the problem. Bob On Mar 25, 2016, at 5:55 PM, Bruce Griffiths wrote: As long as BNC connectors are avoided as their phase shift isnt that stable.. A small mechanical disturbance will change it significantly. Actually low noise PN measurement systems can be very sensitive to cable movement. Bolting modules to a metal baseplate helps a lot as does using intermodule connections comprising SMA(m)-SMA(m) barrels rather than cables. There's also the question of mixer port termination.The nist paper by Walls and Stein indicates that capacitive termination of the IF port may be effective in reducing noise whilst maintaining a flat response fro dc to around 50KHz.Small value resistors in series with the RF and LO ports are then useful in reducing the VSWR. Bruce On Saturday, 26 March 2016 10:10 AM, Bob Camp wrote: Hi On Mar 25, 2016, at 1:55 PM, jimlux wrote: On 3/25/16 5:07 AM, Bob Camp wrote: Hi The reverse isolation issue is indeed one of the weaknesses of this setup. For testing OCXO’s isolation is not a big deal. A normal OCOX has very good output buffering to give it the stability you are after. If you are running (maybe) a VCO with no buffering, that assumption falls apart. The VCO will / can injection lock through the mixer. In that case you *do* need an amp to provide enough isolation to prevent the injection lock. But if someone were building a little module for a cheap and cheerful noise analyzer, then the buffer amp would be a separate module. That’s how I have always done it in the past. The need for the bufferer is rare enough that including it in the basic analyzer module is not cost effective. The HP 3048 has the same basic issue (isolation) and they made the same decision there. Bob ___ 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. - No virus found in this message. Checked by AVG - www.avg.com Version: 2016.0.7497 / Virus Database: 4545/11882 - Release Date: 03/25/16 ___ 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] Spectrum Analyzer Specifications --> phase noise test set
Hi The sensitivity of BNC connectors goes up quite a bit as they wear out. Both sides of the connection are subject to wear. Replacing both sides is often the only solution when they get noisy. That said, “screw down” connectors are a better way to go. The “capacitive loading” termination of the mixer is something that a number of us tried to reproduce when the paper came out. Even after fairly extensive conversations with the authors, the effect seems be quite difficult to reproduce. It certainly is not a “general solution” to the problem. Bob > On Mar 25, 2016, at 5:55 PM, Bruce Griffiths > wrote: > > As long as BNC connectors are avoided as their phase shift isnt that stable.. > A small mechanical disturbance will change it significantly. Actually low > noise PN measurement systems can be very sensitive to cable movement. Bolting > modules to a metal baseplate helps a lot as does using intermodule > connections comprising SMA(m)-SMA(m) barrels rather than cables. > There's also the question of mixer port termination.The nist paper by Walls > and Stein indicates that capacitive termination of the IF port may be > effective in reducing noise whilst maintaining a flat response fro dc to > around 50KHz.Small value resistors in series with the RF and LO ports are > then useful in reducing the VSWR. > Bruce > > >On Saturday, 26 March 2016 10:10 AM, Bob Camp wrote: > > > > Hi > >> On Mar 25, 2016, at 1:55 PM, jimlux wrote: >> >> On 3/25/16 5:07 AM, Bob Camp wrote: >>> Hi >>> >>> The reverse isolation issue is indeed one of the weaknesses of this setup. >>> For testing >>> OCXO’s isolation is not a big deal. A normal OCOX has very good output >>> buffering >>> to give it the stability you are after. If you are running (maybe) a VCO >>> with no buffering, that >>> assumption falls apart. The VCO will / can injection lock through the >>> mixer. In that >>> case you *do* need an amp to provide enough isolation to prevent the >>> injection lock. >>> >> >> >> But if someone were building a little module for a cheap and cheerful noise >> analyzer, then the buffer amp would be a separate module. > > That’s how I have always done it in the past. The need for the bufferer is > rare enough that including it in the > basic analyzer module is not cost effective. The HP 3048 has the same basic > issue (isolation) and they made > the same decision there. > > Bob > > >> >> ___ >> 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] Spectrum Analyzer Specifications --> phase noise test set
As long as BNC connectors are avoided as their phase shift isnt that stable.. A small mechanical disturbance will change it significantly. Actually low noise PN measurement systems can be very sensitive to cable movement. Bolting modules to a metal baseplate helps a lot as does using intermodule connections comprising SMA(m)-SMA(m) barrels rather than cables. There's also the question of mixer port termination.The nist paper by Walls and Stein indicates that capacitive termination of the IF port may be effective in reducing noise whilst maintaining a flat response fro dc to around 50KHz.Small value resistors in series with the RF and LO ports are then useful in reducing the VSWR. Bruce On Saturday, 26 March 2016 10:10 AM, Bob Camp wrote: Hi > On Mar 25, 2016, at 1:55 PM, jimlux wrote: > > On 3/25/16 5:07 AM, Bob Camp wrote: >> Hi >> >> The reverse isolation issue is indeed one of the weaknesses of this setup. >> For testing >> OCXO’s isolation is not a big deal. A normal OCOX has very good output >> buffering >> to give it the stability you are after. If you are running (maybe) a VCO >> with no buffering, that >> assumption falls apart. The VCO will / can injection lock through the >> mixer. In that >> case you *do* need an amp to provide enough isolation to prevent the >> injection lock. >> > > > But if someone were building a little module for a cheap and cheerful noise > analyzer, then the buffer amp would be a separate module. That’s how I have always done it in the past. The need for the bufferer is rare enough that including it in the basic analyzer module is not cost effective. The HP 3048 has the same basic issue (isolation) and they made the same decision there. Bob > > ___ > 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] Spectrum Analyzer Specifications --> phase noise test set
On Friday, March 25, 2016 10:55:59 AM jimlux wrote: > On 3/25/16 5:07 AM, Bob Camp wrote: > > Hi > > > > The reverse isolation issue is indeed one of the weaknesses of this setup. > > For testing OCXO’s isolation is not a big deal. A normal OCOX has very > > good output buffering to give it the stability you are after. If you are > > running (maybe) a VCO with no buffering, that assumption falls apart. The > > VCO will / can injection lock through the mixer. In that case you *do* > > need an amp to provide enough isolation to prevent the injection lock. > But if someone were building a little module for a cheap and cheerful > noise analyzer, then the buffer amp would be a separate module. > > ___ > 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. Yes that way one can tailor the amp gain and/or operating frequency to the task at hand. As a general guide for amps employing 1-2 transistors if a reverse isolation of 40dB or more is required: For a gain of 0-3dB a CB stage offers the lowest noise. For higher gain and/or output push pull CB stages are required. For a gain of 3-10dB a series shunt feedback amplifier can be effective particularly if the output is taken from a transformer connected between the collector and the shunt feedback resistor. This configuration is useful in that one can employ the same output transformer for a wide range of gains. The gain is changed by changing the value of a pair of resistors. HP used discrete series shunt feedback stages in some of their PN measurement gear. However these suffered from relatively poor close in PN which can be cured by substituting a lower noise biasing system. As long as the amp uses low noise biasing and low noise supplies together with sufficient RF negative feedback then its flicker noise wont be an issue. With a cross correlation system employing independent amps for each channel an amp with a noise figure < 6dB will usually suffice in that the added noise penalty can be traded off against a longer averaging time to reduce the system PN noise. Bruce ___ 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] Spectrum Analyzer Specifications --> phase noise test set
Hi > On Mar 25, 2016, at 1:55 PM, jimlux wrote: > > On 3/25/16 5:07 AM, Bob Camp wrote: >> Hi >> >> The reverse isolation issue is indeed one of the weaknesses of this setup. >> For testing >> OCXO’s isolation is not a big deal. A normal OCOX has very good output >> buffering >> to give it the stability you are after. If you are running (maybe) a VCO >> with no buffering, that >> assumption falls apart. The VCO will / can injection lock through the >> mixer. In that >> case you *do* need an amp to provide enough isolation to prevent the >> injection lock. >> > > > But if someone were building a little module for a cheap and cheerful noise > analyzer, then the buffer amp would be a separate module. That’s how I have always done it in the past. The need for the bufferer is rare enough that including it in the basic analyzer module is not cost effective. The HP 3048 has the same basic issue (isolation) and they made the same decision there. Bob > > ___ > 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] Spectrum Analyzer Specifications --> phase noise test set
On 3/25/16 5:07 AM, Bob Camp wrote: Hi The reverse isolation issue is indeed one of the weaknesses of this setup. For testing OCXO’s isolation is not a big deal. A normal OCOX has very good output buffering to give it the stability you are after. If you are running (maybe) a VCO with no buffering, that assumption falls apart. The VCO will / can injection lock through the mixer. In that case you *do* need an amp to provide enough isolation to prevent the injection lock. But if someone were building a little module for a cheap and cheerful noise analyzer, then the buffer amp would be a separate module. ___ 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] Spectrum Analyzer Specifications --> phase noise test set
Hi The reverse isolation issue is indeed one of the weaknesses of this setup. For testing OCXO’s isolation is not a big deal. A normal OCOX has very good output buffering to give it the stability you are after. If you are running (maybe) a VCO with no buffering, that assumption falls apart. The VCO will / can injection lock through the mixer. In that case you *do* need an amp to provide enough isolation to prevent the injection lock. Bob > On Mar 25, 2016, at 12:27 AM, Bruce Griffiths > wrote: > > http://www.ko4bb.com/getsimple/index.php?id=low-noise-high-reverse-isolation-low-distortion-rf-amplifier > Bruce > > > >On Friday, 25 March 2016 4:57 PM, Bruce Griffiths > wrote: > > > If 40-50dB reverse isolation is sufficient one can easily build suitable low > gain (<10dB) amps with a single RF transistor (plus output transformer > together with a low frequency transistor plus LED for bias stabilisation). > Retrofitting a similar biasing scheme to the RF amps in some early HP PN > measurement gear apparently does wonders for their PN at low offsets. > One could even use a square wave drive from the output of a 74UHS125 or > similar CMOS buffer to drive the phase detector input. There is a NIST paper > that indicates a square wave LO drive for some mixers improves the > performance somewhat. > > If reverse isolation isnt an issue a pushpull transformer feedback Norton amp > works well. > > I just bought the HELA10's on evaluation PCBs complete with brass metalwork.. > > Bruce > > > >On Friday, 25 March 2016 4:02 PM, Bob Camp wrote: > > > Hi > > If you think the HELA10 is fun at 10 MHz, try it at 1 MHz :) > > The RPD-1 is a 1 MHz to 100 MHz part. That pretty well covers *most* of the > low > phase noise OCXO’s that people find running around in their junk boxes. To be > “general purpose”, an amp would need to cover the same range. With two OCXO’s > and two mixers, you would need 4 amps if they are after the splitters. By the > time you > get even the HELA10’s on heatsinks and boards you probably are around $40 an > amplifier. Finding a part that is “as good as” the HELA10 is at 100 MHz, but > at 1 MHz, > is not very easy …. > > = > > Sort of on a bit different part of the same topic: > > There is nothing magic about the RPD-1 other than it is easy to dead bug and > attach leaded > parts to. If one is doing a pc board, the SYPD-1 is the same thing in a > cheaper > surface mount package. The $5.70 you save will pay for a few square inches of > pc board. > > Bob > > >> On Mar 24, 2016, at 9:31 PM, Bruce Griffiths >> wrote: >> >> Actually if you split the signal and then amplify each output independently >> then the PN performance of the RF amps is not too critical in that cross >> correlation averages the amplifier PN down as well as that of the >> mixers.I've done this with the Timepod using quite noisy amps as nothing >> else was immediately to hand.It just takes a little longer but works very >> well. I measured the output PN noise of an LTC6957 evaluation board this way >> using a couple of minicircuits HELA10s which are fairly noisy at 10MHz. >> If you don't need a PN floor below -180dBc/Hz then there are simple >> inexpensive one transistor (plus another for biasing) circuits that will >> achieve a few dB of gain with a PN noise floor well below -170dBc/Hz.The >> only real limitation is due to the presence of anti correlated thermal noise >> at the splitter outputs. >> >> Bruce >> >> >> On Friday, 25 March 2016 2:06 PM, Bob Camp wrote: >> >> >> Hi >> >> That’s another good point about the need to work out a target device. Both >> of the possible target devices I mentioned have enough channels to do at >> least a >> dual channel measurement. That would add another mixer and a pair of power >> splitters along with another amp chain. >> >> The other part of that news is the RF drive power required goes up. You can >> do a pretty good job >> of saturating an RPD-1 with +7 dbm. Most (but not all) OCXO’s and other >> gizmos will >> provide that without any amplifiers involved. Adding a 3 db splitter gets >> you into the 10 dbm >> range. That is getting fairly close to the limit for a lot of devices. >> >> You can add an amp. The ones that work without impacting the phase noise of >> a high quality >> OCXO cost as much as the audio cards or USB devices. Cost wise, I’d keep >> that sort >> of thing off the main board. >> >> So what is the second channel worth? >> >> The basic single channel design will get you into the -173 to -176 dbc / Hz >> range on a fairly high >> power pair of OCXO’s. The cross correlation “stuff” will get you past that >> point. Is that worth taking >> the BOM (without board and power supply) up to $80 or so? Consider that with >> the board and >> power supply, it likely is over $100. >> >> Would I do it as an accessory to a Janus or QA401? Maybe. You would need to >> pic
Re: [time-nuts] Spectrum Analyzer Specifications --> phase noise test set
http://www.ko4bb.com/getsimple/index.php?id=low-noise-high-reverse-isolation-low-distortion-rf-amplifier Bruce On Friday, 25 March 2016 4:57 PM, Bruce Griffiths wrote: If 40-50dB reverse isolation is sufficient one can easily build suitable low gain (<10dB) amps with a single RF transistor (plus output transformer together with a low frequency transistor plus LED for bias stabilisation). Retrofitting a similar biasing scheme to the RF amps in some early HP PN measurement gear apparently does wonders for their PN at low offsets. One could even use a square wave drive from the output of a 74UHS125 or similar CMOS buffer to drive the phase detector input. There is a NIST paper that indicates a square wave LO drive for some mixers improves the performance somewhat. If reverse isolation isnt an issue a pushpull transformer feedback Norton amp works well. I just bought the HELA10's on evaluation PCBs complete with brass metalwork.. Bruce On Friday, 25 March 2016 4:02 PM, Bob Camp wrote: Hi If you think the HELA10 is fun at 10 MHz, try it at 1 MHz :) The RPD-1 is a 1 MHz to 100 MHz part. That pretty well covers *most* of the low phase noise OCXO’s that people find running around in their junk boxes. To be “general purpose”, an amp would need to cover the same range. With two OCXO’s and two mixers, you would need 4 amps if they are after the splitters. By the time you get even the HELA10’s on heatsinks and boards you probably are around $40 an amplifier. Finding a part that is “as good as” the HELA10 is at 100 MHz, but at 1 MHz, is not very easy …. = Sort of on a bit different part of the same topic: There is nothing magic about the RPD-1 other than it is easy to dead bug and attach leaded parts to. If one is doing a pc board, the SYPD-1 is the same thing in a cheaper surface mount package. The $5.70 you save will pay for a few square inches of pc board. Bob > On Mar 24, 2016, at 9:31 PM, Bruce Griffiths > wrote: > > Actually if you split the signal and then amplify each output independently > then the PN performance of the RF amps is not too critical in that cross > correlation averages the amplifier PN down as well as that of the mixers.I've > done this with the Timepod using quite noisy amps as nothing else was > immediately to hand.It just takes a little longer but works very well. I > measured the output PN noise of an LTC6957 evaluation board this way using a > couple of minicircuits HELA10s which are fairly noisy at 10MHz. > If you don't need a PN floor below -180dBc/Hz then there are simple > inexpensive one transistor (plus another for biasing) circuits that will > achieve a few dB of gain with a PN noise floor well below -170dBc/Hz.The only > real limitation is due to the presence of anti correlated thermal noise at > the splitter outputs. > > Bruce > > > On Friday, 25 March 2016 2:06 PM, Bob Camp wrote: > > > Hi > > That’s another good point about the need to work out a target device. Both > of the possible target devices I mentioned have enough channels to do at > least a > dual channel measurement. That would add another mixer and a pair of power > splitters along with another amp chain. > > The other part of that news is the RF drive power required goes up. You can > do a pretty good job > of saturating an RPD-1 with +7 dbm. Most (but not all) OCXO’s and other > gizmos will > provide that without any amplifiers involved. Adding a 3 db splitter gets you > into the 10 dbm > range. That is getting fairly close to the limit for a lot of devices. > > You can add an amp. The ones that work without impacting the phase noise of a > high quality > OCXO cost as much as the audio cards or USB devices. Cost wise, I’d keep > that sort > of thing off the main board. > > So what is the second channel worth? > > The basic single channel design will get you into the -173 to -176 dbc / Hz > range on a fairly high > power pair of OCXO’s. The cross correlation “stuff” will get you past that > point. Is that worth taking > the BOM (without board and power supply) up to $80 or so? Consider that with > the board and > power supply, it likely is over $100. > > Would I do it as an accessory to a Janus or QA401? Maybe. You would need to > pick one or > the other. In the case of the Janus, there are more software issues and some > noise floor testing. > The QA401 is mighty expensive. The original idea was to use the sound card > you already have …. > > Bob > > >> On Mar 24, 2016, at 5:30 PM, Bruce Griffiths >> wrote: >> >> If the software implements acquisition of cross power spectra >> Then one could implement a near state of the art cross correlation PN test >> set >> based on this. >> With a suitable preamp the sound card could also be used for power supply >> and >> reference noise measurement. >> >> Bruce >> >> On Thursday, March 24, 2016 04:54:47 PM Bob Camp wrote: >>> Hi >>> >>> The board is pre
Re: [time-nuts] Spectrum Analyzer Specifications --> phase noise test set
Hi If you think the HELA10 is fun at 10 MHz, try it at 1 MHz :) The RPD-1 is a 1 MHz to 100 MHz part. That pretty well covers *most* of the low phase noise OCXO’s that people find running around in their junk boxes. To be “general purpose”, an amp would need to cover the same range. With two OCXO’s and two mixers, you would need 4 amps if they are after the splitters. By the time you get even the HELA10’s on heatsinks and boards you probably are around $40 an amplifier. Finding a part that is “as good as” the HELA10 is at 100 MHz, but at 1 MHz, is not very easy …. = Sort of on a bit different part of the same topic: There is nothing magic about the RPD-1 other than it is easy to dead bug and attach leaded parts to. If one is doing a pc board, the SYPD-1 is the same thing in a cheaper surface mount package. The $5.70 you save will pay for a few square inches of pc board. Bob > On Mar 24, 2016, at 9:31 PM, Bruce Griffiths > wrote: > > Actually if you split the signal and then amplify each output independently > then the PN performance of the RF amps is not too critical in that cross > correlation averages the amplifier PN down as well as that of the mixers.I've > done this with the Timepod using quite noisy amps as nothing else was > immediately to hand.It just takes a little longer but works very well. I > measured the output PN noise of an LTC6957 evaluation board this way using a > couple of minicircuits HELA10s which are fairly noisy at 10MHz. > If you don't need a PN floor below -180dBc/Hz then there are simple > inexpensive one transistor (plus another for biasing) circuits that will > achieve a few dB of gain with a PN noise floor well below -170dBc/Hz.The only > real limitation is due to the presence of anti correlated thermal noise at > the splitter outputs. > > Bruce > > >On Friday, 25 March 2016 2:06 PM, Bob Camp wrote: > > > Hi > > That’s another good point about the need to work out a target device. Both > of the possible target devices I mentioned have enough channels to do at > least a > dual channel measurement. That would add another mixer and a pair of power > splitters along with another amp chain. > > The other part of that news is the RF drive power required goes up. You can > do a pretty good job > of saturating an RPD-1 with +7 dbm. Most (but not all) OCXO’s and other > gizmos will > provide that without any amplifiers involved. Adding a 3 db splitter gets you > into the 10 dbm > range. That is getting fairly close to the limit for a lot of devices. > > You can add an amp. The ones that work without impacting the phase noise of a > high quality > OCXO cost as much as the audio cards or USB devices. Cost wise, I’d keep > that sort > of thing off the main board. > > So what is the second channel worth? > > The basic single channel design will get you into the -173 to -176 dbc / Hz > range on a fairly high > power pair of OCXO’s. The cross correlation “stuff” will get you past that > point. Is that worth taking > the BOM (without board and power supply) up to $80 or so? Consider that with > the board and > power supply, it likely is over $100. > > Would I do it as an accessory to a Janus or QA401? Maybe. You would need to > pick one or > the other. In the case of the Janus, there are more software issues and some > noise floor testing. > The QA401 is mighty expensive. The original idea was to use the sound card > you already have …. > > Bob > > >> On Mar 24, 2016, at 5:30 PM, Bruce Griffiths >> wrote: >> >> If the software implements acquisition of cross power spectra >> Then one could implement a near state of the art cross correlation PN test >> set >> based on this. >> With a suitable preamp the sound card could also be used for power supply >> and >> reference noise measurement. >> >> Bruce >> >> On Thursday, March 24, 2016 04:54:47 PM Bob Camp wrote: >>> Hi >>> >>> The board is pretty non-critical. It’s 90% audio. The biggest hassle is a >>> power supply. You would *like* a fairly high voltage, at least if you are >>> driving a spectrum analyzer. That may not be quite the case with a sound >>> card. It depends a *lot* which one you are running. Something like a QA401: >>> >>> https://www.quantasylum.com/content/Products/QA401.aspx >>> >>> Would make a good target device. It’s based on the AKM 5397 So might some >>> Janus boards. They are based on the earlier(?) AKM 5394. The QA401 has the >>> advantage of a nice box and full USB isolation (ground loops are a pain).. >>> It also has drivers and all the OS hooks. The Janus is a bit more “DIY” >>> with no drivers or interface (let alone isolation). The Janus is < 1/4 the >>> price. >>> >>> The high voltage (+/- 18V linear regulated) supply approach makes a lot of >>> sense with the QA401. It probably does not make as much sense with the >>> Janus. Switching regulators of any sort are something I would strongly >>> recommend against in a system
