Re: [time-nuts] WWVB PM Time Questions
Paul, I finally got the WWVB d-psk-r board built. I have it connected to an Arduino UNO and to my NEO-6 GPS module.The GPS module has been re-programmed to 19.2k baud and only the GPRMC NEMA message is being sent. The MC34141 is running at 12 volts and I am using 620 ohm resistors to drive the transformer center taps. I am feeding a 60 kHz sine wave into pin 8 of the transformer through a 0.47 uF non-polarized cap. I have my scope connected to pin 1 of the transformer through a 0.47 uF non-polarized cap. The 1 PPS LED connected to pin 2 of the 74HCT14 is following the 1 PPS led on the GPS board. I see the phase LED on the d-psk-r board blink at random. The LED on the UNO blinks in unison with the phase led. What should I see on the scope? I don't see anything that looks normal. No sine wave, just random pulses. I slowed the 60 kHz sine wave down to 30 Hz but still no sine wave. If I have the scan rate on the scope set to 100 msec, I would expect to see 1 second worth of sine waves. What should the output level of the 60 kHz signal from my AWG be set to? I have tried a few settings from 25 mV to 1 volt. Ray, AB7HE ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Symmetricom 58536A
Thanks much, Kevin, interesting point. If I connect the Tbolt to the PD5120's DC Block port, and another GPSDO to the DC Pass port, Heather shows the Tbolt's status with "Tracking satellites" in green. However, "Antenna open" continues to display in yellow. But it seems there was a more mundane explanation here. While moving cables around, I noticed that Heather's status display changed when I repositioned the cable between the splitter and the Tbolt. After replacing it with a fresh cable, the Tbolt is now working fine with the 58536A. If I can throw out another question, I'm not entirely clear on how the 58536A handles bias voltages from multiple receivers. There is a label with "DC Power" and an arrow next to each of its four receiver ports. The Symmetricom information note on the unit that I was able to find doesn't say anything at all about bias voltages. I've heard two conflicting statements from other users. One said the 58536A defaults to using only port 1 for bias voltage (unlikely to me, given the labels). Another said the 58536A combines any voltages present on any of the receiver ports and passes them on to the antenna, but blocks any from going back to any of the receivers (sounds more likely). Does anyone believe they have the last word on this? Thanks again, Frank On 8/17/20 4:22 PM, Kevin Rowett wrote: Does the setup with the PD5120 work if the TBolt is connected to either port? Some GPS receivers look to see if the antenna is drawing current, to determine if it’s alive. With a splitter, the receiver might not see an antenna current. I seem to recall the TBolt had a setting for that. KR On Aug 17, 2020, at 3:04 PM, Frank O'Donnell wrote: Based on a recommendation here sometime back, I bought a Symmetricom 58536A distribution amplifier so that up to four GPSDOs can share my rooftop Lucent 26db twist antenna. When I connect the antenna to its port on the 58536A, and a Trimble Thunderbolt to port 1, Heather shows no antenna connection on the Thunderbolt. By contrast, when I use the antenna and Thunderbolt (and/or another GPSDO) with a 2-port Instock PD5120 splitter/combiner, all devices function normally. The 58536A information note says it needs +4.5 to 13vdc. The antenna requires 3.3 to 5vdc. A multimeter measures +4.951vdc on the Thunderbolt's antenna port. If anyone has suggestions, I'll be very grateful. Frank ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Symmetricom 58536A
Does the setup with the PD5120 work if the TBolt is connected to either port? Some GPS receivers look to see if the antenna is drawing current, to determine if it’s alive. With a splitter, the receiver might not see an antenna current. I seem to recall the TBolt had a setting for that. KR > On Aug 17, 2020, at 3:04 PM, Frank O'Donnell wrote: > > Based on a recommendation here sometime back, I bought a Symmetricom 58536A > distribution amplifier so that up to four GPSDOs can share my rooftop Lucent > 26db twist antenna. > > When I connect the antenna to its port on the 58536A, and a Trimble > Thunderbolt to port 1, Heather shows no antenna connection on the > Thunderbolt. By contrast, when I use the antenna and Thunderbolt (and/or > another GPSDO) with a 2-port Instock PD5120 splitter/combiner, all devices > function normally. > > The 58536A information note says it needs +4.5 to 13vdc. The antenna requires > 3.3 to 5vdc. A multimeter measures +4.951vdc on the Thunderbolt's antenna > port. > > If anyone has suggestions, I'll be very grateful. > > Frank > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] ! PPS Source
Ed, Good work digging deep into that. I remember hearing about someone playing with the Oncore oscillator. It was Robin Giffard, one of the key architects behind the hp SmartClock series (58503A, Z3801A, etc.). A copy of his paper: "Estimation of GPS Ionospheric Delay Using L1 Code and Carrier Phase Observables" https://apps.dtic.mil/sti/pdfs/ADA497270.pdf You'll see the Motorola Oncore VP mentioned in several places. He used a 5061B and a simple M/N PLL to give 3590 / 188 MHz = 19.0957 MHz. I don't recall any other papers describing a similar experiment. In that era the Oncore VP was one of the favorite timing receivers. You would think if there was any merit to the clock hack then lots of people or products would do it. But AFAIK, none did, not even hp. All of these GPSDO had microprocessors and TIC onboard so using the GPS receiver generated sawtooth correction message is all they needed. /tvb On 8/17/2020 1:53 PM, ed breya wrote: Thanks all, for the info on this issue. It does indeed look doable to experiment with phase-locking the GPS RX module's internal clock to the ultimate 10 MHz GPSDO output. That is, doable, but not necessarily easy or without problems. I dug up my old notes and info from about ten years ago, and found I had studied it quite extensively, and had some various schemes sketched out already - I forgot about all this. In the notes I found some pages from US Patents 4,785,463, and 5,745,741, which are pertinent to the Motorola Oncore RX units. I also found page 26 of a document "Remote Frequency Calibration: The NIST Frequency Measurement and Analysis Service," which talks about it too. The internal clock appears to be 19.096 MHz nominal, +/- 2 ppm, from a TCXO, that may or may not have voltage tuning too, depending on the model. The '463 patent appears to be about the original overall design, while the '741 is about reducing the sawtooth error by doing coarse digital corrections in the counter system, while also fine tuning the VCTXO, to get an integer clock frequency under all conditions. It mentions the Oncore model as prior art, and the resulting sawtooth error. As I understand it, the overall process disclosed is to allow for the TCXO to drift to any frequency in range, but automatically tweak it slightly to make sure it's an integer (Hz ) value, and set the counter system to divide by that same integer value, so the 1 PPS output is consistent, without sawtooth error. So, if the clock is nearly exactly right on, the counter divides by 19,096,000, and it figures out how to fine tune the clock to keep it there. If the drift goes beyond the fine range to say all the way to the upper stated limit of +38 Hz, the counter is set to divide by 19,096,038, and the clock is again tweaked to keep it close to that integer Hz. How it does all this is disclosed in the patent, but I haven't studied it enough to say any more. It looks like this improvement was in a later model, or was perhaps never actually used, since this was around the time that Motorola was departing the GPS business. I assume the older Oncores like mine do not have any of this improvement, so are subject to both the clock drift and the sawtooth. But, one thing I got from this, is that if the nominal clock and divide numbers match, and are fixed at 19,096,000, then replacing the original clock with a sufficiently clean synthesized external clock should work too. I have a number of possible options, depending on the actual original TCXO. If it's also voltage-tuned, but that isn't utilized, then it can stay, but needs circuit mods to release and access the tune signal. The clock signal is accessible at the TCXO, or possibly less risky in 2X form 38.192 MHz from the downconverter IC. This would be the best option, to make an external PLL to tweak it. BTW I have a spare GPS RX unit - I would not risk taking the Z3801A out of commission and messing around with it. If the TCXO has no tuning ability, then a new clock signal needs to be made. Of all the schemes I sketched out back then, the most straightforward seems to be simply adding 4.096 MHz from a VCXO, PLLed to 10 MHz, and 15 MHz derived directly from the 10. These can all be scaled up in frequency in various arrangements, and use standard binary frequency XOs. The next notch up for instance, is 8.192 MHz + 30 MHz giving twice the clock, and so forth. Unfortunately, this method is additive in frequency, which I hate - I prefer to take the difference of two much higher frequencies, which is so much easier to filter. I don't yet see any ways to do a difference method without using special frequencies, so for now I assume regular old standard XO frequencies will have to do, and the filter designs will need to be fancier. The PLLing seems to be straightforward. I can get a decent 16 kHz comparison frequency with simple integer dividing, like 4.096 MHz/256 = 10 MHz/625, but would like to get
[time-nuts] Symmetricom 58536A
Based on a recommendation here sometime back, I bought a Symmetricom 58536A distribution amplifier so that up to four GPSDOs can share my rooftop Lucent 26db twist antenna. When I connect the antenna to its port on the 58536A, and a Trimble Thunderbolt to port 1, Heather shows no antenna connection on the Thunderbolt. By contrast, when I use the antenna and Thunderbolt (and/or another GPSDO) with a 2-port Instock PD5120 splitter/combiner, all devices function normally. The 58536A information note says it needs +4.5 to 13vdc. The antenna requires 3.3 to 5vdc. A multimeter measures +4.951vdc on the Thunderbolt's antenna port. If anyone has suggestions, I'll be very grateful. Frank ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] ! PPS Source
Thanks all, for the info on this issue. It does indeed look doable to experiment with phase-locking the GPS RX module's internal clock to the ultimate 10 MHz GPSDO output. That is, doable, but not necessarily easy or without problems. I dug up my old notes and info from about ten years ago, and found I had studied it quite extensively, and had some various schemes sketched out already - I forgot about all this. In the notes I found some pages from US Patents 4,785,463, and 5,745,741, which are pertinent to the Motorola Oncore RX units. I also found page 26 of a document "Remote Frequency Calibration: The NIST Frequency Measurement and Analysis Service," which talks about it too. The internal clock appears to be 19.096 MHz nominal, +/- 2 ppm, from a TCXO, that may or may not have voltage tuning too, depending on the model. The '463 patent appears to be about the original overall design, while the '741 is about reducing the sawtooth error by doing coarse digital corrections in the counter system, while also fine tuning the VCTXO, to get an integer clock frequency under all conditions. It mentions the Oncore model as prior art, and the resulting sawtooth error. As I understand it, the overall process disclosed is to allow for the TCXO to drift to any frequency in range, but automatically tweak it slightly to make sure it's an integer (Hz ) value, and set the counter system to divide by that same integer value, so the 1 PPS output is consistent, without sawtooth error. So, if the clock is nearly exactly right on, the counter divides by 19,096,000, and it figures out how to fine tune the clock to keep it there. If the drift goes beyond the fine range to say all the way to the upper stated limit of +38 Hz, the counter is set to divide by 19,096,038, and the clock is again tweaked to keep it close to that integer Hz. How it does all this is disclosed in the patent, but I haven't studied it enough to say any more. It looks like this improvement was in a later model, or was perhaps never actually used, since this was around the time that Motorola was departing the GPS business. I assume the older Oncores like mine do not have any of this improvement, so are subject to both the clock drift and the sawtooth. But, one thing I got from this, is that if the nominal clock and divide numbers match, and are fixed at 19,096,000, then replacing the original clock with a sufficiently clean synthesized external clock should work too. I have a number of possible options, depending on the actual original TCXO. If it's also voltage-tuned, but that isn't utilized, then it can stay, but needs circuit mods to release and access the tune signal. The clock signal is accessible at the TCXO, or possibly less risky in 2X form 38.192 MHz from the downconverter IC. This would be the best option, to make an external PLL to tweak it. BTW I have a spare GPS RX unit - I would not risk taking the Z3801A out of commission and messing around with it. If the TCXO has no tuning ability, then a new clock signal needs to be made. Of all the schemes I sketched out back then, the most straightforward seems to be simply adding 4.096 MHz from a VCXO, PLLed to 10 MHz, and 15 MHz derived directly from the 10. These can all be scaled up in frequency in various arrangements, and use standard binary frequency XOs. The next notch up for instance, is 8.192 MHz + 30 MHz giving twice the clock, and so forth. Unfortunately, this method is additive in frequency, which I hate - I prefer to take the difference of two much higher frequencies, which is so much easier to filter. I don't yet see any ways to do a difference method without using special frequencies, so for now I assume regular old standard XO frequencies will have to do, and the filter designs will need to be fancier. The PLLing seems to be straightforward. I can get a decent 16 kHz comparison frequency with simple integer dividing, like 4.096 MHz/256 = 10 MHz/625, but would like to get it as high as possible, without resorting to fancier schemes. Fractional-N is not in the cards here, I don't think. It would be nice if for some reason a 19.096 MHz VCXO module - or even just a crystal - was available for cheap, but I doubt such exists outside of the Oncore line. Maybe a TCXO from a junker would do, but again, it has to have voltage tuning too, and I don't know if any had that. (One of my more far fetched schemes even pictured thermal tuning - TEC heating and cooling the TCXO module - but imagine the nightmare of characterizing the part and the dynamics, and the mechanical and control loop issues.) So anyway, I think I can do it with the additive VCXO combo, but doubt I ever will - there are too many projects to worry about without reviving this one, but it's fun to ponder. BTW one last thing is that in my collection, I have parts of an ancient (ca 1990), huge Trimble L1/L2 GPSDO. I was going to share some info on it, but
