Products > Test Equipment
bg7tbl gpsdo master reference
Ringmodulator:
--- Quote from: mojoe on February 10, 2024, 01:03:23 pm ---After 12 hours, I'm getting from 0-3 mHz low on this model. I had read about the offset on earlier models, but was under the impression that it was fixed on recent models (I don't remember the year).
I'm still curious as to why mine came with such a huge delay. This is certainly not a default.
I also have a NanoVNA H4. It was my intention to flash the PFA firmware on it and test again, with that. I've not used Timelab. Are there any recommended settings for this type of measurement?
--- End quote ---
I too did the conversion of a NanoVNA-4H to TinyPFA by reflashing it.
Getting it to work with Timelab was straigt forward, even for a Timalab noob like me.
I have the settings on another pc. If you have problems, I can check.
mojoe:
Some results, after logging data for 24 hours. I was using my HP 11 digit counter (showing me single mHz) with it's external reference hooked to my HP 58540A GPSDO, which has been running continuously for about 2.5 years. Both GPSDO's were on the same HP timing antenna via a splitter (I plan on getting an amplified antenna splitter, but the passive one seemed to work fine). Data was collected using a Prolific GPIB-USB dongle and EZGPIB, setting the counter to a 10 second gate time. I have not done a survey-in yet.
If I make a graph with all 24 hours of data, it will be too huge, and still won't show the fine data. So, I'll summarize. At 140 seconds, it stabilized at +/- 0-4 mHz. At that point the Alarm LED went out. It stayed +/-0-4 mHz for several hours. Later, it stayed +/-0-3 mHz for several more hours. During the last several hours it settled on 10000000.000 and 9999999.999 (mostly 10000000.000). That LSD may just be due to my counter.
Looking at the data, it is interesting that the frequency is low much more often that it is high. I assume that has something to do with the firmware and how it tunes the OCXO.
Here is a small graph, showing the initial warm up. It gets within 4 mHz of 10 MHz quickly. However, this was not a total cold start, as earlier I had it running while I looked at the GPS module with u-center. It was then unplugged for 10-15 minutes.
I conclude that this revision hardware/firmware does not have the frequency offset reported for earlier revisions (at least to the mHz resolution).
Next, after I finish setting up a spare mini-PC, I'll run Lady heather on this GPSDO, using /rxu to force u-blox binary mode. I understand that this will make a difference in what is reported to the software vs the default NMEA mode that is autodetected. I'll also do a survery-in for a day or two with LH. I'm new to LH, so I'm not sure what I'll see.
Later, I plan on flashing my NanoVNA H4 with the PFA firmware. I have no idea how much better data I'll get with a PFA vs my HP counter. I hope I can get a few more digits, to see how this GPSDO really performs.
As mentioned above, my counter only lets me see to single mHz. If I did the math right, 1 mHz from 10 MHz is 1E-10. Good enough for anything I need, but a good GPSDO should be 100 times better than that.
mojoe:
I got LH running. I had some trouble with the built-in Comm 1 port, so for now I'm using a USB-serial adapter. After a second read through of the docs, I set a bunch of command line options (Edit: I forced ubx mode). I can't find how to turn off the satellite displays. I'd like to have the graph wider.
For some reason, I can't get any of the video resolution options to give me a full screen display. I'm using a 1080p TV via HDMI, but F11 and /vh crashes, /vf and /vc=1920x1080 gives me a smaller screen, and everything I tried has fonts too small to read. The best so far is the default of 1024x768.
After fooling around a bit, I turned on SBAS (GPS was already on) and started a 48 hour survey with SP. Shortly after, I did a screen capture.
I understand what most of the text means. Are the satellite signal levels (dBc) good? I'm going through a passive splitter with my HP timing antenna. I understand what the graph in the upper right is. I'm not so sure what the graph at the bottom is showing me. I did turn on ADEV.
If I understand things, after the survey is done, I can turn off SBAS, then do an EE to write the surveyed position back to the u-blox GPS. Then I may want to increase the elevation mask and save that.
Any words of wisdom or enlightenment about any of this is appreciated.
mojoe:
Before starting LH, I fired up my HP 8920B to see what the 10 MHz sinewave looked like. The level measured about 12 dBm. The second harmonic was at -35 dBm (-47 dBc) and the other harmonics were in the noise. For harmonics, I set the span from 0-100 MHz.
I understand that the OCXO puts out a squarewave, so the LPF is doing an excellent job.
FPSychotic:
Hi, I won a bid if this GPSDO with no display, CTS oscillator and original labeled Neo7 , I don't remember if 7n or 7m , but I can open again of needed.
It gets lock quite fast in indoor with my antenna that is triband and 3-V.
I made and db9 cable with TX to RX to a ftdi and displayed in ucenter , 8.1 old version used in Neo7 years and the last one 23.xx I think. With both U-center versions can see the sats it locks, 10 average in the room, and precision is absolutely enough with that, I wont put outside the antenna.
The problem is that even reading the sats, it doesn't read the config, firmware version, or anything and I can change nothing, all the gnss tab boxes appears detached, the firmware empty...any idea of why this behaviour?
Maybe my cable is wrong and I should buy a commercial one?
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