Re: [time-nuts] Correcting jitter on the 1 PPS signalfrom a GPS receiver.
A lot of devices have a low output impedance so that the signal can be split using a TEE adapter with little loss or need for a distribution amplifier. However, the cables must be impedance matched at far end, scope input, to prevent reflections which are the source of the ringing. You can match the impedance at the source and you will get a reflection which will then be absorbed by the source resistance. One way to do this is to get a small 15 turn pot about 100 Ohms put it, in series with the input source and adjust it until the ringing is gone or you can put it at the far end ,input of the scope, to ground and do the same. But the best solution is to get a good feed thru 50 Ohm terminator and put it on the input of the scope. Bill -- Message: 1 Date: Sun, 14 Sep 2014 09:58:54 -0700 From: Said Jackson saidj...@aol.com Peter, That depends. To use 1M Ohms input impedance, you need a 50 Ohms series impedance at the driver chip. Most sources such as the 58503A and Thunderbolt violate that requirement by having only a couple of Ohms output impedance, and are thus not suitable and do need the 50 Ohms termination at the scope least you get horrible ringing as shown in Tom's plots from yesterday. From: time-nuts [time-nuts-boun...@febo.com] on behalf of time-nuts-requ...@febo.com [time-nuts-requ...@febo.com] Sent: Sunday, September 14, 2014 1:11 PM To: time-nuts@febo.com Subject: time-nuts Digest, Vol 122, Issue 42 Send time-nuts mailing list submissions to time-nuts@febo.com To subscribe or unsubscribe via the World Wide Web, visit https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts or, via email, send a message with subject or body 'help' to time-nuts-requ...@febo.com You can reach the person managing the list at time-nuts-ow...@febo.com When replying, please edit your Subject line so it is more specific than Re: Contents of time-nuts digest... Today's Topics: 1. Re: Correcting jitter on the 1 PPSsignalfromaGPSreceiver. (Said Jackson) 2. Re: Correcting jitter on the 1 PPSsignalfromaGPSreceiver. (Peter Reilley) 3. Re: Correcting jitter on the 1 PPSsignalfromaGPSreceiver. (Said Jackson) 4. Fwd: Correcting jitter on the 1 PPS signalfromaGPSreceiver. (Said Jackson) -- Message: 1 Date: Sun, 14 Sep 2014 09:58:54 -0700 From: Said Jackson saidj...@aol.com To: Peter Reilley pe...@reilley.com Cc: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Correcting jitter on the 1 PPS signalfromaGPSreceiver. Message-ID: a77b8502-096e-4d03-864e-4a63af3a9...@aol.com Content-Type: text/plain; charset=us-ascii Peter, That depends. To use 1M Ohms input impedance, you need a 50 Ohms series impedance at the driver chip. Most sources such as the 58503A and Thunderbolt violate that requirement by having only a couple of Ohms output impedance, and are thus not suitable and do need the 50 Ohms termination at the scope least you get horrible ringing as shown in Tom's plots from yesterday. However that means you are pumping up to 100mA through your coax, and scope termination. That makes your coax ground jump many 10's of millivolts (depending on cable length and quality). This IR induced ground jump now also shows up on your 10MHz coax and messes with that signal, as the 1PPS return current partially goes through the 10MHz coax shield and generates a voltage rise on the shield. It's a cluster You can take a multimeter and actually measure the voltage drop on your coax cable shield from one connector to the other. On units with longer 1PPS pulse you see the multimeter twitch once per second (Symmetricom XLI for example) even on a short 1m cable. But if you look at Tom's plots you see that there is some high frequency ringing on the 58503A 1PPS when terminated into 1M, I am not sure thats coming from cable reflections. For those high frequency rings a 1G scope may be better to see what's really going on in the driver. Think about it this way: why would you want to drive a 50 Ohms coax with a 5 Ohms output impedance? That's an absolutely horrible impedance mismatch. But that is what the Trimble Thunderbolt does, and likely also the Resolution-T.. Resulting in ringing up to 10V on your cable. Bye, Said Sent from my iPad On Sep 14, 2014, at 9:04, Peter Reilley pe...@reilley.com wrote: I tried removing the termination and got a little better than 4 nS risetime. Isn't the ringing frequency simply a function of the length of the coax? Isn't it the price you pay for mismatched impedances? Pete. -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Said Jackson via time-nuts Sent: Sunday,
Re: [time-nuts] Correcting jitter on the 1 PPS signalfrom a GPS receiver.
Is there any reason (other than cost) not to both series-terminate the source and parallel-terminate the sink? When I was dealing with analog video, the standard distribution method was : 1. Buffer amplifier with high input impedance, very low output impedance, and a gain of 2 (so 1 V P-P input becomes 2 V P-P out) 2. A series 75 ohm resistor from the amp output to each individual video output. This formed a 2:1 voltage divider with the 75 ohm coax to give 1 V P-P on the cable. It also isolates the loads from each other. 3. A single video signal could be looped through multiple high impedance loads. 4. 75 ohm parallel termination at the far end of the signal path (usually on the last device). This way, every device along the way saw an undistorted copy of the signal. The buffer amplifier sees a simple resistive load. And any reflections are absorbed at both ends of the cable. - Dave On 15/09/2014 02:04, Fuqua, Bill L wrote: A lot of devices have a low output impedance so that the signal can be split using a TEE adapter with little loss or need for a distribution amplifier. However, the cables must be impedance matched at far end, scope input, to prevent reflections which are the source of the ringing. You can match the impedance at the source and you will get a reflection which will then be absorbed by the source resistance. One way to do this is to get a small 15 turn pot about 100 Ohms put it, in series with the input source and adjust it until the ringing is gone or you can put it at the far end ,input of the scope, to ground and do the same. But the best solution is to get a good feed thru 50 Ohm terminator and put it on the input of the scope. Bill ___ 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] newcomer
Hi the list, Just wanted to introduce myself for my 1st message. I'm Stephane, 40, living in France, at the moment working in RF electronics for a particles accelerator lab. I'm hamradio as well, and I do enjoy especially weak and accurate signals. I'm desiging various RF circuits. Current design is a universal PLL able to operate from 0.5 to 6 GHz depending on the VCO and supposed to be low-jitter (1ps) regarding the application. I'm also starting a new design of low noise PLL and there will be probably a lot of question arising... I'm starting with the 1 GHz LO made upon a 100 MHz VCXO + multipliers/filters/MMICs. I want to focus deeper on low phase noise/jitter, synchronization and low-noise PLL techniques. I believe this is a good place for most of these topics. Cheers Stephane ___ 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] Correcting jitter on the 1 PPSsignalfromaGPSreceiver.
How important are all these cable / termination / impedance issues for 1PPS signals? I know ringing and reflections are undesirable in many applications. But for 1PPS? I often use pick whatever cable, termination, and trigger level gives the cleanest edge, the best risetime. What happens to the signal tens or hundreds of nanoseconds after the edge seems irrelevant to me. Could one of you RF experts comment? /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] Correcting jitter on the 1 PPSsignalfromaGPSreceiver.
Fast risetime pulses _are_ RF and need to be treated as such. Tom - Original Message - From: Tom Van Baak t...@leapsecond.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Monday, September 15, 2014 9:43 AM Subject: Re: [time-nuts] Correcting jitter on the 1 PPSsignalfromaGPSreceiver. How important are all these cable / termination / impedance issues for 1PPS signals? I know ringing and reflections are undesirable in many applications. But for 1PPS? I often use pick whatever cable, termination, and trigger level gives the cleanest edge, the best risetime. What happens to the signal tens or hundreds of nanoseconds after the edge seems irrelevant to me. Could one of you RF experts comment? /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] Correcting jitter on the 1 PPSsignalfromaGPSreceiver.
Some good refs on coax driving showing scope traces for ringing etc: http://www.ti.com/lit/an/snla043/snla043.pdf http://www.ti.com/lit/an/sboa075/sboa075.pdf On Mon, Sep 15, 2014 at 9:43 AM, Tom Van Baak t...@leapsecond.com wrote: How important are all these cable / termination / impedance issues for 1PPS signals? I know ringing and reflections are undesirable in many applications. But for 1PPS? I often use pick whatever cable, termination, and trigger level gives the cleanest edge, the best risetime. What happens to the signal tens or hundreds of nanoseconds after the edge seems irrelevant to me. Could one of you RF experts comment? /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] Correcting jitter on the 1 PPSsignalfromaGPSreceiver.
On 9/15/2014 10:01 AM, Tom Miller wrote: Fast risetime pulses _are_ RF and need to be treated as such. You say that as if simply saying it provides an explanation, or even a reason. Exactly what ill effect on a triggered measurement is there if one does not terminate a PPS signal properly? Does/can termination increase the slew rate or make the speed of propagation more consistent, which might make the measurement more accurate? Like Tom said, what comes after the leading edge of a PPS signal (which is the measurement trigger) seems irrelevant. A simple though experiment. If I take a high impedance measurement at a tap 1M from the source, and the cable ends another 100M away, how can the termination or lack thereof at that end effect my measurement of a single event? It's over 700 ns round trip away? If I repeat that event 1/sec, is it any different? I can see where there would be a difference when I get close to a 700 ns cycle time, and likely before because of ringing. But for a 1 second cycle? Someone will have to provide more than a dismissive just because to convince me. ___ 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] Correcting jitter on the1 PPSsignalfromaGPSreceiver.
You need not have a properly terminated transmission line but you must then worry about the bounce. If you understand the size of the bounce and have a system that will not suffer false triggering then you will be OK. There are some worries however. It is hard to predict the exact size of the bounce since any measurements that you take necessarily affect the impedance of the line and therefore the characteristics of the bounce. If you change the components of your transmission line then you effect the size of the bounce. High quality (low loss) coax will have a larger bounce than crappy coax. The terminating impendence that you do have affects the bounce. Is the receiving device 1 M ohm? Is it 1 K ohm. The capacitance also has an effect. Is it 10 pF, 100 pF, 1000 pF? Complex impedances are lots of fun to figure out in these situations. A 50 Ohm terminator generally swamps any complex impedance effects and they can generally be ignored, The length of the coax will effect the size and position of the bounce. Do you know the size of the bounce? Do you know your system's trigger set point? Can you adjust the set point? If you use a properly terminated cable these worries mostly go away. You can run without a termination, it is just easier and more reliable with it. Pete. -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Mike S Sent: Monday, September 15, 2014 10:29 AM To: time-nuts@febo.com Subject: Re: [time-nuts] Correcting jitter on the1 PPSsignalfromaGPSreceiver. On 9/15/2014 10:01 AM, Tom Miller wrote: Fast risetime pulses _are_ RF and need to be treated as such. You say that as if simply saying it provides an explanation, or even a reason. Exactly what ill effect on a triggered measurement is there if one does not terminate a PPS signal properly? Does/can termination increase the slew rate or make the speed of propagation more consistent, which might make the measurement more accurate? Like Tom said, what comes after the leading edge of a PPS signal (which is the measurement trigger) seems irrelevant. A simple though experiment. If I take a high impedance measurement at a tap 1M from the source, and the cable ends another 100M away, how can the termination or lack thereof at that end effect my measurement of a single event? It's over 700 ns round trip away? If I repeat that event 1/sec, is it any different? I can see where there would be a difference when I get close to a 700 ns cycle time, and likely before because of ringing. But for a 1 second cycle? Someone will have to provide more than a dismissive just because to convince me. ___ 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] Correcting jitter on the 1 PPSsignalfromaGPSreceiver.
Hi guys, Tried to bring my point across, but I guess I failed to do so properly. What happens after the edge is very important because what happens after the edge settles is up to 100mA DC current is flowing through all the coaxes AND your building ground. Pumping ~5V into 50 Ohms (Thunderbolt) results in up to 100mA DC current flowing. This current flows out into the center conductor then through the 50 Ohms termination resistor at the sink and then back through ALL your grounds due to the finite resistance of your coax. This includes the instruments' AC power cord, as well as any 10MHz coax you have connected! This DC ground current now does many bad things: 1) it can corrode the connectors over time in humid environments (eg shipboard) 2) it causes measurable and significant (~0.5W!) heating in the termination resistor ( I have IR video that shows the termination resistor blink like a christmas tree once a second) 3) it causes significant dips in the source power supply and heating of the driver ICs in the source 4) it causes a high voltage drop across all coax connections which results in a corresponding shift in the ground potential of the 10MHz signal and thus results in amplitude modulation of the 10MHz signal (CMOS). RG-142 shield has 0.0075 ohms per meter, so the AM modulation of the 10MHz signal over several meters could be in the millivolts - not conducive for measuring stability in ppt 5) if the termination fails or you leave the coax end-termination unconnected then your driver (a number of standard AC gates in parallel in case of the Thunderbolt) will get the full brunt of the reflected pulse which will be up to 10V for a significant amount of time so you are over-stressing that gate. If the termination fails or is disabled, your counter input or scope input may also be overstressed by the double amplitude. On the falling edge it gets even worse: the reflections generate negative voltages far below ground level and can also cause driver over-stress. In summary: End-termination is designed for maximum power transfer for RF signals. It should not be used for transmitting DC signals such as 1PPS signals (the 1PPS pulse is a very high frequency AC signal until the reflections settle in some 10's of nanoseconds, then it is a DC signal) Series termination such as used for reflected wave switching (ie PCI) is the way to go for 1PPS signals and has essentially no drawbacks for fast rising edges other than that a resistor must be inserted at the output of the driver. Hope I made the advantages of series rather than end termination clear. I understand that we all were taught in school that a coax needs to be terminated, and series termination is just that - but at the other end of the cable which is somewhat counter intuitive. The above except item 1) is easy to verify and a lot if fun to do. All you have to do is insert that single series resistor after the driving gates and remove the end-termination and your system will be updated to 21st century standards. Btw I have extensive scope plots comparing series- to end-termination over 10+ feet of coax if anyone is interested. Bye, Said Sent From iPhone On Sep 15, 2014, at 6:43, Tom Van Baak t...@leapsecond.com wrote: How important are all these cable / termination / impedance issues for 1PPS signals? I know ringing and reflections are undesirable in many applications. But for 1PPS? I often use pick whatever cable, termination, and trigger level gives the cleanest edge, the best risetime. What happens to the signal tens or hundreds of nanoseconds after the edge seems irrelevant to me. Could one of you RF experts comment? /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] newcomer
Hi Stephanie, Welcome to the list! We designed a 1GHz crystal LO for PLLs (the ULN-1G) using an off the shelf miniature 500MHz crystal oscillator which is run at 3 rd overtone internally then using a diode doubler and a steep bandpass filter using several Mini Circuits ceramic filters and a 20dBm amp. Works like a charm and has phase noise very close to theoretical.. Bye, Said Sent From iPhone On Sep 15, 2014, at 5:50, steph.rey steph@wanadoo.fr wrote: Hi the list, Just wanted to introduce myself for my 1st message. I'm Stephane, 40, living in France, at the moment working in RF electronics for a particles accelerator lab. I'm hamradio as well, and I do enjoy especially weak and accurate signals. I'm desiging various RF circuits. Current design is a universal PLL able to operate from 0.5 to 6 GHz depending on the VCO and supposed to be low-jitter (1ps) regarding the application. I'm also starting a new design of low noise PLL and there will be probably a lot of question arising... I'm starting with the 1 GHz LO made upon a 100 MHz VCXO + multipliers/filters/MMICs. I want to focus deeper on low phase noise/jitter, synchronization and low-noise PLL techniques. I believe this is a good place for most of these topics. Cheers Stephane ___ 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] Finally, Success
My daughter and I were discussing what she does for a living with time and phase as a geophysicist and relating that to what I'm trying to do with my GPSDOengine. I explained that I was trying to keep the frequency accurate and stable, while also keeping the phase near a target of 180 degrees. And suddenly, I realized that that's not what I was actually doing. For the I term of PID, I was integrating on phase position, which was never going to work. So, I made a change to start integrating on the phase change from second to second (i.e. frequency error), and I think this is finally performing correctly. The DAC is now very flat, and the phase is moving around as would be expected from Bob's and Tom's comments on the LEA-6T. Here's an ADEV of the GPSDO's OCXO vs the 10811 in my 5335A. It covers a timeframe from about 11:00PM last night to about 11:00AM this morning. This is with the PID running as a PI controller with very small P and I gain values. http://evoria.net/AE6RV/TIC/GPSDO.vs.HP10811.png Bob - AE6RV ___ 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] newcomer
Hello Said, Thanks for the answer. Sounds interresting. Do you have a description of that ? Especially a phase noise plot ? As said, I'm planning to use a VCXO (low cost and low noise) at 100 MHz followed by a MMIC (ERA) and a 500 MHz 3-cells helical filter from Temwell. Then a doubler from minicircuit, an other MMIC and a 3-cell helical filter at 1 GHz... Cheers Stephane On Mon, 15 Sep 2014 09:17:01 -0700, Said Jackson via time-nuts time-nuts@febo.com wrote: Hi Stephanie, Welcome to the list! We designed a 1GHz crystal LO for PLLs (the ULN-1G) using an off the shelf miniature 500MHz crystal oscillator which is run at 3 rd overtone internally then using a diode doubler and a steep bandpass filter using several Mini Circuits ceramic filters and a 20dBm amp. Works like a charm and has phase noise very close to theoretical.. Bye, Said Sent From iPhone On Sep 15, 2014, at 5:50, steph.rey steph@wanadoo.fr wrote: Hi the list, Just wanted to introduce myself for my 1st message. I'm Stephane, 40, living in France, at the moment working in RF electronics for a particles accelerator lab. I'm hamradio as well, and I do enjoy especially weak and accurate signals. I'm desiging various RF circuits. Current design is a universal PLL able to operate from 0.5 to 6 GHz depending on the VCO and supposed to be low-jitter (1ps) regarding the application. I'm also starting a new design of low noise PLL and there will be probably a lot of question arising... I'm starting with the 1 GHz LO made upon a 100 MHz VCXO + multipliers/filters/MMICs. I want to focus deeper on low phase noise/jitter, synchronization and low-noise PLL techniques. I believe this is a good place for most of these topics. Cheers Stephane ___ 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] newcomer
Hi, It sounds like all my messages need moderator approbation. Is it the rule on the list or a technical problem at my side ? Cheers Stephane On Mon, 15 Sep 2014 09:17:01 -0700, Said Jackson via time-nuts time-nuts@febo.com wrote: Hi Stephanie, Welcome to the list! We designed a 1GHz crystal LO for PLLs (the ULN-1G) using an off the shelf miniature 500MHz crystal oscillator which is run at 3 rd overtone internally then using a diode doubler and a steep bandpass filter using several Mini Circuits ceramic filters and a 20dBm amp. Works like a charm and has phase noise very close to theoretical.. Bye, Said Sent From iPhone On Sep 15, 2014, at 5:50, steph.rey steph@wanadoo.fr wrote: Hi the list, Just wanted to introduce myself for my 1st message. I'm Stephane, 40, living in France, at the moment working in RF electronics for a particles accelerator lab. I'm hamradio as well, and I do enjoy especially weak and accurate signals. I'm desiging various RF circuits. Current design is a universal PLL able to operate from 0.5 to 6 GHz depending on the VCO and supposed to be low-jitter (1ps) regarding the application. I'm also starting a new design of low noise PLL and there will be probably a lot of question arising... I'm starting with the 1 GHz LO made upon a 100 MHz VCXO + multipliers/filters/MMICs. I want to focus deeper on low phase noise/jitter, synchronization and low-noise PLL techniques. I believe this is a good place for most of these topics. Cheers Stephane ___ 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] newcomer
Hi Stephanie, I have a similar issue, I can never tell if my messages post or not, some I get back instantly others never show up in my inbox. I think the mail server was just updated.. To answer your questions: 1) attached is the PN plot of the 1.0GHz version. 2) Here is a datasheet for the part: http://www.jackson-labs.com/index.php/products/uln_1g The tricky part in your proposed setup will be getting a 100MHz crystal with low enough phase noise so that the 20log(N/M) added phase noise won't be a problem - +20dB added after all. On our part some of the tricky design issues were size and power as well as the high output power of +22dBm, and a requirement to maintain the output power to within 0.5dB over the entire -40C to +85C temperature range. bye, Said In a message dated 9/15/2014 09:40:37 Pacific Daylight Time, steph@wanadoo.fr writes: Hi, It sounds like all my messages need moderator approbation. Is it the rule on the list or a technical problem at my side ? Cheers Stephane On Mon, 15 Sep 2014 09:17:01 -0700, Said Jackson via time-nuts time-nuts@febo.com wrote: Hi Stephanie, Welcome to the list! We designed a 1GHz crystal LO for PLLs (the ULN-1G) using an off the shelf miniature 500MHz crystal oscillator which is run at 3 rd overtone internally then using a diode doubler and a steep bandpass filter using several Mini Circuits ceramic filters and a 20dBm amp. Works like a charm and has phase noise very close to theoretical.. Bye, Said Sent From iPhone On Sep 15, 2014, at 5:50, steph.rey steph@wanadoo.fr wrote: Hi the list, Just wanted to introduce myself for my 1st message. I'm Stephane, 40, living in France, at the moment working in RF electronics for a particles accelerator lab. I'm hamradio as well, and I do enjoy especially weak and accurate signals. I'm desiging various RF circuits. Current design is a universal PLL able to operate from 0.5 to 6 GHz depending on the VCO and supposed to be low-jitter (1ps) regarding the application. I'm also starting a new design of low noise PLL and there will be probably a lot of question arising... I'm starting with the 1 GHz LO made upon a 100 MHz VCXO + multipliers/filters/MMICs. I want to focus deeper on low phase noise/jitter, synchronization and low-noise PLL techniques. I believe this is a good place for most of these topics. Cheers Stephane ___ 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. 1006030 BUT AT 1GHZ.png Description: Binary data ___ 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] Correcting jitter on the 1 PPSsignalfromaGPSreceiver.
Looks like this email did not make it: Hi guys, Tried to bring my point across, but I guess I failed to do so properly. What happens after the edge is very important because what happens after the edge settles is up to 100mA DC current is flowing through all the coaxes AND your building ground. Pumping ~5V into 50 Ohms (Thunderbolt) results in up to 100mA DC current flowing. This current flows out into the center conductor then through the 50 Ohms termination resistor at the sink and then back through ALL your grounds due to the finite resistance of your coax. This includes the instruments' AC power cord, as well as any 10MHz coax you have connected! This DC ground current now does many bad things: 1) it can corrode the connectors over time in humid environments (eg shipboard) 2) it causes measurable and significant (~0.5W!) heating in the termination resistor ( I have IR video that shows the termination resistor blink like a christmas tree once a second) 3) it causes significant dips in the source power supply and heating of the driver ICs in the source 4) it causes a high voltage drop across all coax connections which results in a corresponding shift in the ground potential of the 10MHz signal and thus results in amplitude modulation of the 10MHz signal (CMOS). RG-142 shield has 0.0075 ohms per meter, so the AM modulation of the 10MHz signal over several meters could be in the millivolts - not conducive for measuring stability in ppt 5) if the termination fails or you leave the coax end-termination unconnected then your driver (a number of standard AC gates in parallel in case of the Thunderbolt) will get the full brunt of the reflected pulse which will be up to 10V for a significant amount of time so you are over-stressing that gate. If the termination fails or is disabled, your counter input or scope input may also be overstressed by the double amplitude. On the falling edge it gets even worse: the reflections generate negative voltages far below ground level and can also cause driver over-stress. In summary: End-termination is designed for maximum power transfer for RF signals. It should not be used for transmitting DC signals such as 1PPS signals (the 1PPS pulse is a very high frequency AC signal until the reflections settle in some 10's of nanoseconds, then it is a DC signal) Series termination such as used for reflected wave switching (ie PCI) is the way to go for 1PPS signals and has essentially no drawbacks for fast rising edges other than that a resistor must be inserted at the output of the driver. Hope I made the advantages of series rather than end termination clear. I understand that we all were taught in school that a coax needs to be terminated, and series termination is just that - but at the other end of the cable which is somewhat counter intuitive. The above except item 1) is easy to verify and a lot if fun to do. All you have to do is insert that single series resistor after the driving gates and remove the end-termination and your system will be updated to 21st century standards. Btw I have extensive scope plots comparing series- to end-termination over 10+ feet of coax if anyone is interested. Bye, Said In a message dated 9/15/2014 06:44:21 Pacific Daylight Time, t...@leapsecond.com writes: How important are all these cable / termination / impedance issues for 1PPS signals? I know ringing and reflections are undesirable in many applications. But for 1PPS? I often use pick whatever cable, termination, and trigger level gives the cleanest edge, the best risetime. What happens to the signal tens or hundreds of nanoseconds after the edge seems irrelevant to me. Could one of you RF experts comment? /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] Correcting jitter on the 1 PPS signalfrom a GPS receiver.
Hi Dave, yes there is a reason. The standard 1PPS signal termination (Thunderbolt etc) used to be 5 Ohms or less series termination into a 50 Ohms coax (yikes), then end-terminate to get rid of all the undesired reflections. Your example below is properly terminating a 75 Ohms coax with a 75 Ohms series termination. The end-termination then becomes optional and affects the signal level at the sink. So if a higher signal level is desired, simply leave off the 75 Ohms end termination. But in the case of the Thunderbolt they don't use a 50 Ohms output impedance, they use something around 5 Ohms. That is the problem here: the total impedance mismatch from the very low source impedance into the 50 Ohms coax. The reason they do that is so that they can generate a proper signal level that is approaching 5V across the 50 Ohms end termination so that the signal remains CMOS compatible. Otherwise if they properly terminated the driver with 50 Ohms they would have a voltage divider and would only generate 2.5V at the sink. bye, Said In a message dated 9/15/2014 06:04:34 Pacific Daylight Time, dave.martind...@gmail.com writes: Is there any reason (other than cost) not to both series-terminate the source and parallel-terminate the sink? When I was dealing with analog video, the standard distribution method was : 1. Buffer amplifier with high input impedance, very low output impedance, and a gain of 2 (so 1 V P-P input becomes 2 V P-P out) 2. A series 75 ohm resistor from the amp output to each individual video output. This formed a 2:1 voltage divider with the 75 ohm coax to give 1 V P-P on the cable. It also isolates the loads from each other. 3. A single video signal could be looped through multiple high impedance loads. 4. 75 ohm parallel termination at the far end of the signal path (usually on the last device). This way, every device along the way saw an undistorted copy of the signal. The buffer amplifier sees a simple resistive load. And any reflections are absorbed at both ends of the cable. - Dave On 15/09/2014 02:04, Fuqua, Bill L wrote: A lot of devices have a low output impedance so that the signal can be split using a TEE adapter with little loss or need for a distribution amplifier. However, the cables must be impedance matched at far end, scope input, to prevent reflections which are the source of the ringing. You can match the impedance at the source and you will get a reflection which will then be absorbed by the source resistance. One way to do this is to get a small 15 turn pot about 100 Ohms put it, in series with the input source and adjust it until the ringing is gone or you can put it at the far end ,input of the scope, to ground and do the same. But the best solution is to get a good feed thru 50 Ohm terminator and put it on the input of the scope. Bill ___ 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] newcomer
Hi Stephane, Welcome. There's nothing wrong on your end. Thanks for asking. Subscription to this list is open to all without approval. Since about a year or two ago postings from new subscribers are moderated. Any technically rich, on-topic posting goes through. /tvb (i5s) On Sep 15, 2014, at 9:40 AM, steph.rey steph@wanadoo.fr wrote: Hi, It sounds like all my messages need moderator approbation. Is it the rule on the list or a technical problem at my side ? Cheers Stephane On Mon, 15 Sep 2014 09:17:01 -0700, Said Jackson via time-nuts time-nuts@febo.com wrote: Hi Stephanie, Welcome to the list! We designed a 1GHz crystal LO for PLLs (the ULN-1G) using an off the shelf miniature 500MHz crystal oscillator which is run at 3 rd overtone internally then using a diode doubler and a steep bandpass filter using several Mini Circuits ceramic filters and a 20dBm amp. Works like a charm and has phase noise very close to theoretical.. Bye, Said Sent From iPhone On Sep 15, 2014, at 5:50, steph.rey steph@wanadoo.fr wrote: Hi the list, Just wanted to introduce myself for my 1st message. I'm Stephane, 40, living in France, at the moment working in RF electronics for a particles accelerator lab. I'm hamradio as well, and I do enjoy especially weak and accurate signals. I'm desiging various RF circuits. Current design is a universal PLL able to operate from 0.5 to 6 GHz depending on the VCO and supposed to be low-jitter (1ps) regarding the application. I'm also starting a new design of low noise PLL and there will be probably a lot of question arising... I'm starting with the 1 GHz LO made upon a 100 MHz VCXO + multipliers/filters/MMICs. I want to focus deeper on low phase noise/jitter, synchronization and low-noise PLL techniques. I believe this is a good place for most of these topics. Cheers Stephane ___ 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] Correcting jitter on the 1 PPSsignalfromaGPSreceiver.
I found the schematics of the Mini-T output circuit. It actually is a single 10 Ohms series resistor (R32) driven by six parallel 74AC04 gates. Thus only a single resistor change on the Mini-T would fix the issue. Since the gates probably have about 2 Ohms equivalent impedance, simply changing R32 to a 47 Ohms resistor would fix the problem. Also, another issue with the end termination happens when driving very long coax cables: RG-142 for example has about 60 Ohms center conductor resistance and 7.5 Ohms shield resistance at 1km length. So the cable DC resistance is almost 70 Ohms at 1km, which would make the voltage across the end termination drop to around 2V from the desired 5V. In this scenario the series terminated system would generate a nice 5V at the end of the cable after the reflections have calmed down (within some us). bye, Said In a message dated 9/15/2014 07:24:27 Pacific Daylight Time, tsho...@gmail.com writes: Some good refs on coax driving showing scope traces for ringing etc: http://www.ti.com/lit/an/snla043/snla043.pdf http://www.ti.com/lit/an/sboa075/sboa075.pdf On Mon, Sep 15, 2014 at 9:43 AM, Tom Van Baak t...@leapsecond.com wrote: How important are all these cable / termination / impedance issues for 1PPS signals? I know ringing and reflections are undesirable in many applications. But for 1PPS? I often use pick whatever cable, termination, and trigger level gives the cleanest edge, the best risetime. What happens to the signal tens or hundreds of nanoseconds after the edge seems irrelevant to me. Could one of you RF experts comment? /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. ___ 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] Correcting jitter on the 1 PPS signalfrom a GPS receiver.
I will agree that the end termination is optional if you are delivering a pulse signal to just one input, which is at the far end of the coax. However, I think there's still a problem with series-only termination when the pulse signal is daisy-chained through multiple inputs. When you apply 5 volts through a 50 ohm terminator to a 50 ohm cable, the instantaneous voltage on the coax is only 2.5 V. A pulse of amplitude 2.5 V travels down the cable, and reflects from the open far end. The reflection travels back along the cable to the source, raising the voltage from 2.5 to 5 V as it passes. A device input located at the far end of the cable sees a single edge of 5 V amplitude, so it's happy. But anything located somewhere along the cable run sees two edges: one from 0 to 2.5 V, then a constant 2.5 V for a period equal to twice the delay of the remaining cable, then another edge from 2.5 to 5 V. Depending on the input threshold, this in-between device might trigger reliably on the first edge, the second edge, or not reliably on either. Having proper far-end termination is critical for analog video, where daisy-chaining is common, and a reflection that's even 1% of the amplitude of the original signal is likely to be visible as a ghost image. With pulse signals, maybe it makes more sense to use one cable per device input, input plus lots of distribution amplifiers and splitters. - Dave On Mon, Sep 15, 2014 at 1:13 PM, S. Jackson via time-nuts time-nuts@febo.com wrote: Hi Dave, yes there is a reason. The standard 1PPS signal termination (Thunderbolt etc) used to be 5 Ohms or less series termination into a 50 Ohms coax (yikes), then end-terminate to get rid of all the undesired reflections. Your example below is properly terminating a 75 Ohms coax with a 75 Ohms series termination. The end-termination then becomes optional and affects the signal level at the sink. So if a higher signal level is desired, simply leave off the 75 Ohms end termination. But in the case of the Thunderbolt they don't use a 50 Ohms output impedance, they use something around 5 Ohms. That is the problem here: the total impedance mismatch from the very low source impedance into the 50 Ohms coax. The reason they do that is so that they can generate a proper signal level that is approaching 5V across the 50 Ohms end termination so that the signal remains CMOS compatible. Otherwise if they properly terminated the driver with 50 Ohms they would have a voltage divider and would only generate 2.5V at the sink. bye, Said In a message dated 9/15/2014 06:04:34 Pacific Daylight Time, dave.martind...@gmail.com writes: Is there any reason (other than cost) not to both series-terminate the source and parallel-terminate the sink? When I was dealing with analog video, the standard distribution method was : 1. Buffer amplifier with high input impedance, very low output impedance, and a gain of 2 (so 1 V P-P input becomes 2 V P-P out) 2. A series 75 ohm resistor from the amp output to each individual video output. This formed a 2:1 voltage divider with the 75 ohm coax to give 1 V P-P on the cable. It also isolates the loads from each other. 3. A single video signal could be looped through multiple high impedance loads. 4. 75 ohm parallel termination at the far end of the signal path (usually on the last device). This way, every device along the way saw an undistorted copy of the signal. The buffer amplifier sees a simple resistive load. And any reflections are absorbed at both ends of the cable. - Dave On 15/09/2014 02:04, Fuqua, Bill L wrote: A lot of devices have a low output impedance so that the signal can be split using a TEE adapter with little loss or need for a distribution amplifier. However, the cables must be impedance matched at far end, scope input, to prevent reflections which are the source of the ringing. You can match the impedance at the source and you will get a reflection which will then be absorbed by the source resistance. One way to do this is to get a small 15 turn pot about 100 Ohms put it, in series with the input source and adjust it until the ringing is gone or you can put it at the far end ,input of the scope, to ground and do the same. But the best solution is to get a good feed thru 50 Ohm terminator and put it on the input of the scope. Bill ___ 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
Re: [time-nuts] Correcting jitter on the 1 PPS signalfrom a GPS receiver.
Hi Dave, what you are describing is reflected wave switching, which works perfectly in applications such as the PCI bus. The PCI bus uses it because it lends itself to extremely low power consumption. Your scenario does not work with end-termination either if you have multiple taps, because the taps would have to a) have very high impedance so as not to disturb the signal traveling down the pipe, and b) not have any cable length associated with them so as to prevent the edge going down into the stub and reflecting back from it, and the stub causing a 25 Ohms impedance drop (due to two 50 Ohms transmission lines in parallel). With the rise-times of sub 1ns (the CSAC GPSDO has a rise and fall time of 500ps typically) any cable length becomes an issue, including the couple of inches of wiring inside the counter and through the T-splitter etc. Another issue is that the timing of the instruments would be all off because of the differing propagation delays through the additional cable. So in the end-terminated world having a stub would only work if the stub does not have any cable length associated with it and very high impedance. How many folks distribute their 1PPS signal through a single coax cable to multiple instruments? This should be done through a 1PPS distribution amp. I agree though that in the analog video world you don't want reflections due to even small impedance mismatches because they cause ghosting. In the digital world where all we care about is that one single rising edge per second ghosting is not an issue. My original point was that the video world got it right: use a 75 Ohms output impedance for a 75 Ohms coax. The 1PPS world did not get it right by driving a 50 Ohms coax with a 10 Ohms output impedance. Bye, Said In a message dated 9/15/2014 10:43:24 Pacific Daylight Time, dave.martind...@gmail.com writes: I will agree that the end termination is optional if you are delivering a pulse signal to just one input, which is at the far end of the coax. However, I think there's still a problem with series-only termination when the pulse signal is daisy-chained through multiple inputs. When you apply 5 volts through a 50 ohm terminator to a 50 ohm cable, the instantaneous voltage on the coax is only 2.5 V. A pulse of amplitude 2.5 V travels down the cable, and reflects from the open far end. The reflection travels back along the cable to the source, raising the voltage from 2.5 to 5 V as it passes. A device input located at the far end of the cable sees a single edge of 5 V amplitude, so it's happy. But anything located somewhere along the cable run sees two edges: one from 0 to 2.5 V, then a constant 2.5 V for a period equal to twice the delay of the remaining cable, then another edge from 2.5 to 5 V. Depending on the input threshold, this in-between device might trigger reliably on the first edge, the second edge, or not reliably on either. Having proper far-end termination is critical for analog video, where daisy-chaining is common, and a reflection that's even 1% of the amplitude of the original signal is likely to be visible as a ghost image. With pulse signals, maybe it makes more sense to use one cable per device input, input plus lots of distribution amplifiers and splitters. - Dave On Mon, Sep 15, 2014 at 1:13 PM, S. Jackson via time-nuts _time-nuts@febo.com_ (mailto:time-nuts@febo.com) wrote: Hi Dave, yes there is a reason. The standard 1PPS signal termination (Thunderbolt etc) used to be 5 Ohms or less series termination into a 50 Ohms coax (yikes), then end-terminate to get rid of all the undesired reflections. Your example below is properly terminating a 75 Ohms coax with a 75 Ohms series termination. The end-termination then becomes optional and affects the signal level at the sink. So if a higher signal level is desired, simply leave off the 75 Ohms end termination. But in the case of the Thunderbolt they don't use a 50 Ohms output impedance, they use something around 5 Ohms. That is the problem here: the total impedance mismatch from the very low source impedance into the 50 Ohms coax. The reason they do that is so that they can generate a proper signal level that is approaching 5V across the 50 Ohms end termination so that the signal remains CMOS compatible. Otherwise if they properly terminated the driver with 50 Ohms they would have a voltage divider and would only generate 2.5V at the sink. bye, Said In a message dated 9/15/2014 06:04:34 Pacific Daylight Time, _dave.martindale@gmail.com_ (mailto:dave.martind...@gmail.com) writes: Is there any reason (other than cost) not to both series-terminate the source and parallel-terminate the sink? When I was dealing with analog video, the standard distribution method was : 1. Buffer amplifier with high input impedance, very low output impedance, and a gain of 2 (so 1
Re: [time-nuts] Correcting jitter on the 1 PPSsignalfromaGPSreceiver.
I don't claim to be able to do the math, but one could probably easily calculate it from the Fourier frequencies by looking at the attenuation by frequency over a 1km lengh: Loss per 100m over frequency: 10M100M400M1300M2300M 7dB14dB28dB 49dB72dB So looking at these numbers I am guesstimating a risetime in the us alongside a good handful of microseconds of propagation delay. bye, Said In a message dated 9/15/2014 11:31:28 Pacific Daylight Time, hmur...@megapathdsl.net writes: Also, another issue with the end termination happens when driving very long coax cables: RG-142 for example has about 60 Ohms center conductor resistance and 7.5 Ohms shield resistance at 1km length. RG-142 is far from low-loss. Does anybody use it at that length? What's the rise time at the end of 1 km with a 1 ns rise time at the input? -- 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] Hydrogen Maser KIT!
Is that all. Sounds like a piece of cake. Regards. Max. K 4 O DS. - Original Message - From: cdel...@juno.com To: time-nuts@febo.com Sent: Sunday, September 14, 2014 12:16 PM Subject: [time-nuts] Hydrogen Maser KIT! Well, I bet that got your attention! My Hydrogen Maser kit arrived recently. It's a surplus Sigma Tau VLBA-112 with an unknown physics package problem that has had its power supply modules, RF receiver modules, synthesizer and cavity servo tuning modules, and a couple other bits removed for spares. Also it has been opened up to the level that the storage bulb could be removed. (Magnetic shields, insulation, and bell jar removed) The two main problems (so far, fingers crossed) are that the palladium silver purifier/leak valve is missing (along with the Hydrogen supply bottle), and that the storage bulb coating looks to be shot. I've been tracing the power supply wiring and design, and should be able to replace the missing stuff easily. Minor problems are fabricating connectors for the ion pumps, replacing one missing oven control module, and finding a Perkin Elmer pump controller (150ma) for a reasonable price. Once the bulb and purifier problems are cured the major efforts will be: -to reassemble the cavity, shields, and bell jar. -bakeout and pumpdown the ion pumps (in isolation) -bakeout and pumpdown the system. -stabilize the ovens and initiate the Hydrogen discharge. Then if oscillation can be achieved the RF system can be built. Replacing the Automatic cavity tuning will come last as it's not needed for basic operation. I plan to add a relay on the input of the EFOS2 Maser that lives here. This will allow the EFOS RF systems to be utilized for testing before having to build up the new receiver. This will be a LONG term effort and I will share the progress as I go along. Some info: Copper cavity loaded with Quartz dielectric cylinder and Quartz bulb. Cavity Q (loaded) 36000 Line Q approx 1.6X10+9 Drift 5 parts in 10-15 per day (Auto tuner on) Temperature sensitivity 1 X 10-14 per degree C `Weight 525 pounds (including backup battery) Tom has kindly posted some PIX at: http://leapsecond.com/corby/maser/ You might want to look at the old posts about homemade Hydrogen Masers starting back in Aug 29 2010. Cheers, Corby ___ 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] Correcting jitter on the 1 PPSsignalfromaGPSreceiver.
Also, another issue with the end termination happens when driving very long coax cables: RG-142 for example has about 60 Ohms center conductor resistance and 7.5 Ohms shield resistance at 1km length. RG-142 is far from low-loss. Does anybody use it at that length? What's the rise time at the end of 1 km with a 1 ns rise time at the input? -- 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] Finally, Success
Bob, On 09/15/2014 06:23 PM, Bob Stewart wrote: My daughter and I were discussing what she does for a living with time and phase as a geophysicist and relating that to what I'm trying to do with my GPSDOengine. I explained that I was trying to keep the frequency accurate and stable, while also keeping the phase near a target of 180 degrees. And suddenly, I realized that that's not what I was actually doing. For the I term of PID, I was integrating on phase position, which was never going to work. So, I made a change to start integrating on the phase change from second to second (i.e. frequency error), and I think this is finally performing correctly. The DAC is now very flat, and the phase is moving around as would be expected from Bob's and Tom's comments on the LEA-6T. Here's an ADEV of the GPSDO's OCXO vs the 10811 in my 5335A. It covers a timeframe from about 11:00PM last night to about 11:00AM this morning. This is with the PID running as a PI controller with very small P and I gain values. http://evoria.net/AE6RV/TIC/GPSDO.vs.HP10811.png For a PID PLL you need to build the phase error properly one way or another being PE = phase_ref - phase_out If you use a TIC, the time difference is simply a variant of the PE value (phase_out to start and phase_ref to stop channels). It may be useful to have a offset value that can be subtracted numerically. A PID on this then becomes f = (PE - PE_prev)/t0 PE_prev = PE Vi = Vi + I*PE Vf = Vi + P*PE + D*f Integrating on the derivate of PE helps in one particular case, when the frequency error is so large that it doesn't lock up easily. This is done like this: f = (PE - PE_prev)/t0 PE_prev = PE Vi = Vi + I*PE + F*f Vf = Vi + P*PE + D*f As you increase the F factor, the rate of frequency learning of I goes quicker, and steers the exponential relaxation of the frequency error before the beat frequency becomes so low that the phase-lock takes over. As we (me and Warren) had a long thread before, turning up F is the same as turning up P. P is proportional to the damping factor P is proportional to the PLL bandwidth I is proportional to the square of the PLL bandwidth Sounds like you had too low P value. I could write the exact formulas up, they are easy to derivate with paper and pen. It is also textbook material. Make sure you have a damping factor of at least 3. Hope it helps. Cheers, Magnus ___ 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] Correcting jitter on the 1 PPS signalfrom a GPS receiver.
dave.martind...@gmail.com said: Is there any reason (other than cost) not to both series-terminate the source and parallel-terminate the sink? With both series and parallel termination, the signal at the receiver is 1/2 the output level of the output driver. That doesn't work well if you use typical CMOS logic chips at both ends. I don't remember ever seeing an app-note describing how to do that cleanly with readily available chips or data sheets for chips designed to solve that problem. An HCT type receiver might work well. Driver is 5V. Half that is 2.5V. Receiver switches at 1.4 (nominal) which is close to half the signal. I don't think anybody makes a similar chip using modern high-speed CMOS technology. When I was dealing with analog video, the standard distribution method was : ... 3. A single video signal could be looped through multiple high impedance loads. 4. 75 ohm parallel termination at the far end of the signal path (usually on the last device). That looped through is important. Most video boxes have 2 connectors per signal. The idea is that the signal gets routed through the box rather than using a T connector. That lets them minimize the stub length. -- 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] Correcting jitter on the 1 PPSsignalfromaGPSreceiver.
So does adding ~80 pF per meter or 8 nF for 100 meters (RG58) to your output have any effect on the risetime? Because that is what it will see with an open cable. I am sure you can make a case for some condition(s) where an unterminated cable will still work. But it is not something we have been shown necessary to make precise measurements (something this group strives for). YMMV, Tom - Original Message - From: Mike S mi...@flatsurface.com To: time-nuts@febo.com Sent: Monday, September 15, 2014 10:29 AM Subject: Re: [time-nuts] Correcting jitter on the 1 PPSsignalfromaGPSreceiver. On 9/15/2014 10:01 AM, Tom Miller wrote: Fast risetime pulses _are_ RF and need to be treated as such. You say that as if simply saying it provides an explanation, or even a reason. Exactly what ill effect on a triggered measurement is there if one does not terminate a PPS signal properly? Does/can termination increase the slew rate or make the speed of propagation more consistent, which might make the measurement more accurate? Like Tom said, what comes after the leading edge of a PPS signal (which is the measurement trigger) seems irrelevant. A simple though experiment. If I take a high impedance measurement at a tap 1M from the source, and the cable ends another 100M away, how can the termination or lack thereof at that end effect my measurement of a single event? It's over 700 ns round trip away? If I repeat that event 1/sec, is it any different? I can see where there would be a difference when I get close to a 700 ns cycle time, and likely before because of ringing. But for a 1 second cycle? Someone will have to provide more than a dismissive just because to convince me. ___ 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] Hydrogen Maser KIT!
Hi Corby, Looks like a nice challenge and lots of fun and learning. A maser or two would not be bad for my lab :) Those Sigma-Taus is known to be pressure sensitive. Might be something to investigate. Cheers, Magnus On 09/14/2014 07:16 PM, cdel...@juno.com wrote: Well, I bet that got your attention! My Hydrogen Maser kit arrived recently. It's a surplus Sigma Tau VLBA-112 with an unknown physics package problem that has had its power supply modules, RF receiver modules, synthesizer and cavity servo tuning modules, and a couple other bits removed for spares. Also it has been opened up to the level that the storage bulb could be removed. (Magnetic shields, insulation, and bell jar removed) The two main problems (so far, fingers crossed) are that the palladium silver purifier/leak valve is missing (along with the Hydrogen supply bottle), and that the storage bulb coating looks to be shot. I've been tracing the power supply wiring and design, and should be able to replace the missing stuff easily. Minor problems are fabricating connectors for the ion pumps, replacing one missing oven control module, and finding a Perkin Elmer pump controller (150ma) for a reasonable price. Once the bulb and purifier problems are cured the major efforts will be: -to reassemble the cavity, shields, and bell jar. -bakeout and pumpdown the ion pumps (in isolation) -bakeout and pumpdown the system. -stabilize the ovens and initiate the Hydrogen discharge. Then if oscillation can be achieved the RF system can be built. Replacing the Automatic cavity tuning will come last as it's not needed for basic operation. I plan to add a relay on the input of the EFOS2 Maser that lives here. This will allow the EFOS RF systems to be utilized for testing before having to build up the new receiver. This will be a LONG term effort and I will share the progress as I go along. Some info: Copper cavity loaded with Quartz dielectric cylinder and Quartz bulb. Cavity Q (loaded) 36000 Line Q approx 1.6X10+9 Drift 5 parts in 10-15 per day (Auto tuner on) Temperature sensitivity 1 X 10-14 per degree C `Weight 525 pounds (including backup battery) Tom has kindly posted some PIX at: http://leapsecond.com/corby/maser/ You might want to look at the old posts about homemade Hydrogen Masers starting back in Aug 29 2010. Cheers, Corby ___ 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] Correcting jitter on the 1 PPS signalfrom a GPS receiver.
Hi These are saturated logic signals. When you terminate both source and load you get an interesting issue with compatible logic levels. For instance: 5V CMOS switches at roughly 2.5V. If you series terminate and load terminate, your destination now sees a 0 to 2.5V signal. Either it’s running 2.5V CMOS and switching at 1.25V or you have a problem. Bob On Sep 15, 2014, at 9:03 AM, Dave Martindale dave.martind...@gmail.com wrote: Is there any reason (other than cost) not to both series-terminate the source and parallel-terminate the sink? When I was dealing with analog video, the standard distribution method was : 1. Buffer amplifier with high input impedance, very low output impedance, and a gain of 2 (so 1 V P-P input becomes 2 V P-P out) 2. A series 75 ohm resistor from the amp output to each individual video output. This formed a 2:1 voltage divider with the 75 ohm coax to give 1 V P-P on the cable. It also isolates the loads from each other. 3. A single video signal could be looped through multiple high impedance loads. 4. 75 ohm parallel termination at the far end of the signal path (usually on the last device). This way, every device along the way saw an undistorted copy of the signal. The buffer amplifier sees a simple resistive load. And any reflections are absorbed at both ends of the cable. - Dave On 15/09/2014 02:04, Fuqua, Bill L wrote: A lot of devices have a low output impedance so that the signal can be split using a TEE adapter with little loss or need for a distribution amplifier. However, the cables must be impedance matched at far end, scope input, to prevent reflections which are the source of the ringing. You can match the impedance at the source and you will get a reflection which will then be absorbed by the source resistance. One way to do this is to get a small 15 turn pot about 100 Ohms put it, in series with the input source and adjust it until the ringing is gone or you can put it at the far end ,input of the scope, to ground and do the same. But the best solution is to get a good feed thru 50 Ohm terminator and put it on the input of the scope. Bill ___ 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] Correcting jitter on the 1 PPSsignalfromaGPSreceiver.
On 9/15/2014 3:04 PM, Tom Miller wrote: So does adding ~80 pF per meter or 8 nF for 100 meters (RG58) to your output have any effect on the risetime? Because that is what it will see with an open cable. It's not nearly that simple. 8 nF distributed along 100 M is not the same as an 8 nF cap at the source. The example I gave was measuring 1 M from the source, then 100 M of cable beyond that. If the signal has a rise time of, say, 20 ns (Thunderbolt max spec), then anything added cable of more than 3 M (~ 10 ns one way) simply doesn't matter - there's no time for anything which happens to the signal beyond that distance to return in less than the rise time. The signal during the rise time can't know whether there's 3 M or 1000 M of additional cable, or whether the far end is terminated or not. I don't pretend to fully understand transmission lines, but I do know the basics. ___ 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] Correcting jitter on the 1 PPSsignalfromaGPSreceiver.
tmiller11...@verizon.net said: So does adding ~80 pF per meter or 8 nF for 100 meters (RG58) to your output have any effect on the risetime? Because that is what it will see with an open cable. That way of thinking only works if the risetime is long relative to the cable length. In this context, long enough is ballpark of 4 to 10 times the prop time of the cable. For long cables, the cable initially looks like the characteristic impedance of the cable. You can see that on a scope with the classic reflection pictures. In vacuum, the speed of light is very close to 1 ft/ns. Coax varies from 60-90% of that. So if you have 10 ft of cable, it's unlikely that your driver is slow enough for the lumped capacitor approximation to be valid. With shorter cables and old gear using HC chips, you might get there. -- 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] newcomer
Thanks for the details. This miniaturized device is nice. There is no information regarding stability. Anything there ? What's the technology inside ? crystal, TCXO ? What is the approx price for a such device ? The VCXO I was targetting is this one : http://www.abracon.com/Precisiontiming/ABLNO.pdf This should bring more or less the same level of PN once multiplied than your ULN_1G. However the frequency accuracy is poor and it needs to be disciplined in most applications. Cheers Stephane De : saidj...@aol.com [mailto:saidj...@aol.com] Envoyé : lundi 15 septembre 2014 18:51 À : steph@wanadoo.fr; time-nuts@febo.com Objet : Re: [time-nuts] newcomer Hi Stephanie, I have a similar issue, I can never tell if my messages post or not, some I get back instantly others never show up in my inbox. I think the mail server was just updated.. To answer your questions: 1) attached is the PN plot of the 1.0GHz version. 2) Here is a datasheet for the part: http://www.jackson-labs.com/index.php/products/uln_1g The tricky part in your proposed setup will be getting a 100MHz crystal with low enough phase noise so that the 20log(N/M) added phase noise won't be a problem - +20dB added after all. On our part some of the tricky design issues were size and power as well as the high output power of +22dBm, and a requirement to maintain the output power to within 0.5dB over the entire -40C to +85C temperature range. bye, Said In a message dated 9/15/2014 09:40:37 Pacific Daylight Time, mailto:steph@wanadoo.fr steph@wanadoo.fr writes: Hi, It sounds like all my messages need moderator approbation. Is it the rule on the list or a technical problem at my side ? Cheers Stephane On Mon, 15 Sep 2014 09:17:01 -0700, Said Jackson via time-nuts mailto:time-nuts@febo.com time-nuts@febo.com wrote: Hi Stephanie, Welcome to the list! We designed a 1GHz crystal LO for PLLs (the ULN-1G) using an off the shelf miniature 500MHz crystal oscillator which is run at 3 rd overtone internally then using a diode doubler and a steep bandpass filter using several Mini Circuits ceramic filters and a 20dBm amp. Works like a charm and has phase noise very close to theoretical.. Bye, Said Sent From iPhone On Sep 15, 2014, at 5:50, steph.rey mailto:steph@wanadoo.fr steph@wanadoo.fr wrote: Hi the list, Just wanted to introduce myself for my 1st message. I'm Stephane, 40, living in France, at the moment working in RF electronics for a particles accelerator lab. I'm hamradio as well, and I do enjoy especially weak and accurate signals. I'm desiging various RF circuits. Current design is a universal PLL able to operate from 0.5 to 6 GHz depending on the VCO and supposed to be low-jitter (1ps) regarding the application. I'm also starting a new design of low noise PLL and there will be probably a lot of question arising... I'm starting with the 1 GHz LO made upon a 100 MHz VCXO + multipliers/filters/MMICs. I want to focus deeper on low phase noise/jitter, synchronization and low-noise PLL techniques. I believe this is a good place for most of these topics. Cheers Stephane ___ time-nuts mailing list -- mailto:time-nuts@febo.com time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- mailto:time-nuts@febo.com time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. --- Ce courrier électronique ne contient aucun virus ou logiciel malveillant parce que la protection avast! Antivirus est active. 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] Correcting jitter on the 1PPS signal from a GPS receiver
has anyone suggested a 50R in series with a capacitor as termination? no DC currents Best Richard ___ 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] newcomer
Hi Stephane, our customer just needed +/-50KHz free-running over all conditions including aging, so stability was not of major concern, and the unit easily performs significantly better than that. We did make a VCO version for PLL disciplining so you can lock it to a GPSDO or in a correlated phase noise test system etc. The stability is thus not really good, but sufficient for Radar applications. The technology is a Crystal oscillator multiplied by 5x internally I think (maybe it was 3x, can't remember), then by 2x externally. Since it is a MilSpec compliant part it is not that low-cost, but it is lower-cost and much higher-performance than the legacy part it replaces. More than $1K for sure though. It also has some additional tricks up its sleeve such as a built-in DC-DC switcher and power supply filter allowing operation from +6V to +15V without affecting output power, and allowing noisy external power supplies to be used, and harmonics lower than -32dBc typically by using the steep ceramic low-pass filters. That Abracom part looks pretty nice too, and your approach should work well too if you can get the 5x multiplier working well. Get a good 10MHz OCXO and use an AD PLL chip such as ADF4002 etc to lock that Abracom part with a pretty small loop BW (100Hz), and you will have the best of both worlds. Bye, Said In a message dated 9/15/2014 16:52:18 Pacific Daylight Time, steph@wanadoo.fr writes: Thanks for the details. This miniaturized device is nice. There is no information regarding stability. Anything there ? What's the technology inside ? crystal, TCXO ? What is the approx price for a such device ? The VCXO I was targetting is this one : http://www.abracon.com/Precisiontiming/ABLNO.pdf This should bring more or less the same level of PN once multiplied than your ULN_1G. However the frequency accuracy is poor and it needs to be disciplined in most applications. Cheers Stephane ___ 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] newcomer
Thanks for your feedback. This is indeed a bit expensive for that application. The x5 multiplier is indeed just the harmonic 5 capture with the helical filter. I'll let you know the outcome. This probably won't beat any expensive ULN source but might be a good starting point for low cost. Worth to try Stephane -Message d'origine- De : time-nuts [mailto:time-nuts-boun...@febo.com] De la part de S. Jackson via time-nuts Envoyé : mardi 16 septembre 2014 02:11 À : time-nuts@febo.com Objet : Re: [time-nuts] newcomer Hi Stephane, our customer just needed +/-50KHz free-running over all conditions including aging, so stability was not of major concern, and the unit easily performs significantly better than that. We did make a VCO version for PLL disciplining so you can lock it to a GPSDO or in a correlated phase noise test system etc. The stability is thus not really good, but sufficient for Radar applications. The technology is a Crystal oscillator multiplied by 5x internally I think (maybe it was 3x, can't remember), then by 2x externally. Since it is a MilSpec compliant part it is not that low-cost, but it is lower-cost and much higher-performance than the legacy part it replaces. More than $1K for sure though. It also has some additional tricks up its sleeve such as a built-in DC-DC switcher and power supply filter allowing operation from +6V to +15V without affecting output power, and allowing noisy external power supplies to be used, and harmonics lower than -32dBc typically by using the steep ceramic low-pass filters. That Abracom part looks pretty nice too, and your approach should work well too if you can get the 5x multiplier working well. Get a good 10MHz OCXO and use an AD PLL chip such as ADF4002 etc to lock that Abracom part with a pretty small loop BW (100Hz), and you will have the best of both worlds. Bye, Said In a message dated 9/15/2014 16:52:18 Pacific Daylight Time, steph@wanadoo.fr writes: Thanks for the details. This miniaturized device is nice. There is no information regarding stability. Anything there ? What's the technology inside ? crystal, TCXO ? What is the approx price for a such device ? The VCXO I was targetting is this one : http://www.abracon.com/Precisiontiming/ABLNO.pdf This should bring more or less the same level of PN once multiplied than your ULN_1G. However the frequency accuracy is poor and it needs to be disciplined in most applications. Cheers Stephane ___ 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. --- Ce courrier électronique ne contient aucun virus ou logiciel malveillant parce que la protection avast! Antivirus est active. 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 lists status report
We've been on the new version of Mailman for a couple of weeks now. The main reason for the update was to work around the DMARC adoption by Yahoo, AOL, and other large ISPs that broke the mailing list model. That seems to be working now. I'll spare the technical details (you can read about it at http://www.febo.com/dmarc.html) but you may notice that some messages show the From line as Al Smith via time-nuts instead of the normal address. Those messages are from users with AOL, Yahoo, and other addresses that enforce DMARC. We rewrite the From address to avoid that issue. Other addresses are unaffected. Overall, this seems to be working well, and it's once again safe for Yahoo and AOL users to subscribe to the list. However, there is one after-effect that we haven't (yet) been able to resolve. Due to updates in some of the system libraries that Mailman uses, the text formatting of some messages has changed. Instead of being formatted in plain ASCII, they are now encoded in base64 format. Unfortunately, some folks see messed up formatting in those messages. It appears that Eudora has this problem; it doesn't handle base64 properly. I'm not aware of other mail readers being affected. I'd love to fix this problem, but at this point I just don't know how. Sorry for the inconvenience to those users. John ___ 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] Hi all
I should drop an email rather than just lurking on this extremely interesting list. I'm in the process of building my first GPSDO, so I have lots to learn and am enjoying the education. This list has been a real eye opener for me. I'm a licensed amateur radio operator looking to move up into the microwave bands, and I spend a lot of time repairing old radio kit for reuse by other operators. As such an accurate time reference is important, hence this project. So far I've based everything on a number of published sites and designs to learn the basics before launching into something more adventurous and am building a simple PLL locked OCXO using a Navman Jupiter Tu60 GPS and an IsoTemp OCXO. Together these will exceed the limitations of my equipment in measurement, so I'll probably have to build a second one for comparison on the DSO or look into other measurement methods to validate the results. Lots to learn... -- -- Teach your kids Science, or somebody else will :/ ja...@ball.net vk2...@google.com callsign: vk2vjb ___ 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] Hi all
Jason, we just did one using the ublox at 1 KHz and I have some boards extra so if you contact me off list I will gladly send you some data and schematic .Can be modified for 10 KHz. Bert Miami In a message dated 9/15/2014 9:46:35 P.M. Eastern Daylight Time, ja...@ball.net writes: I should drop an email rather than just lurking on this extremely interesting list. I'm in the process of building my first GPSDO, so I have lots to learn and am enjoying the education. This list has been a real eye opener for me. I'm a licensed amateur radio operator looking to move up into the microwave bands, and I spend a lot of time repairing old radio kit for reuse by other operators. As such an accurate time reference is important, hence this project. So far I've based everything on a number of published sites and designs to learn the basics before launching into something more adventurous and am building a simple PLL locked OCXO using a Navman Jupiter Tu60 GPS and an IsoTemp OCXO. Together these will exceed the limitations of my equipment in measurement, so I'll probably have to build a second one for comparison on the DSO or look into other measurement methods to validate the results. Lots to learn... -- -- Teach your kids Science, or somebody else will :/ ja...@ball.net vk2...@google.com callsign: vk2vjb ___ 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] Correcting jitter on the 1 PPS signalfrom a GPS receiver.
depend how do you terminate the, cable if the cable's impedance is Z, use two terminating resistors each R =2Z, one is connected to thee ground the other is connected to the supply voltage of the receiving chip, that way although the cables input and output termination will eat up half of the signal voltage [since the two resistors at the end of the cable are for AC parallel and the two 2Z parallel is =Z ], it will be still enough since the left over 2,5V level change will be centered at the threshold of the input device... 73 Alex On 9/15/2014 2:48 PM, Bob Camp wrote: Hi These are saturated logic signals. When you terminate both source and load you get an interesting issue with compatible logic levels. For instance: 5V CMOS switches at roughly 2.5V. If you series terminate and load terminate, your destination now sees a 0 to 2.5V signal. Either it’s running 2.5V CMOS and switching at 1.25V or you have a problem. Bob On Sep 15, 2014, at 9:03 AM, Dave Martindale dave.martind...@gmail.com wrote: Is there any reason (other than cost) not to both series-terminate the source and parallel-terminate the sink? When I was dealing with analog video, the standard distribution method was : 1. Buffer amplifier with high input impedance, very low output impedance, and a gain of 2 (so 1 V P-P input becomes 2 V P-P out) 2. A series 75 ohm resistor from the amp output to each individual video output. This formed a 2:1 voltage divider with the 75 ohm coax to give 1 V P-P on the cable. It also isolates the loads from each other. 3. A single video signal could be looped through multiple high impedance loads. 4. 75 ohm parallel termination at the far end of the signal path (usually on the last device). This way, every device along the way saw an undistorted copy of the signal. The buffer amplifier sees a simple resistive load. And any reflections are absorbed at both ends of the cable. - Dave On 15/09/2014 02:04, Fuqua, Bill L wrote: A lot of devices have a low output impedance so that the signal can be split using a TEE adapter with little loss or need for a distribution amplifier. However, the cables must be impedance matched at far end, scope input, to prevent reflections which are the source of the ringing. You can match the impedance at the source and you will get a reflection which will then be absorbed by the source resistance. One way to do this is to get a small 15 turn pot about 100 Ohms put it, in series with the input source and adjust it until the ringing is gone or you can put it at the far end ,input of the scope, to ground and do the same. But the best solution is to get a good feed thru 50 Ohm terminator and put it on the input of the scope. Bill ___ 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.
