Products > Test Equipment
bg7tbl gpsdo master reference
mojoe:
I'd say that's a definite yes.
FPSychotic:
Something wrong, I connected PIN5 (gpsdo's GND I guess, as it's the GND pin of RS232) to the GND im the FTDI adapter and will stop even of receiving.
I bought a RS232 to USB , but I think what I have should work
mojoe:
After letting LH run its precision survey for 48 hours, I used u-center to enter those fixed coordinates into the GPS receiver. I also turned off SBAS and set the elevation mask to 15 degrees. To make sure that the changes stuck, I power cycled the GPSDO and checked again.
After powering the GPSDO again, the LOCK LED came on in seconds. It took right at two minutes for the ALARM LED to go out. This time, I turned on ADEV in LH. I let it run overnight.
After running about nine hours since the last power up, I get the ADEV numbers shown in the picture. LH says this about ADEV:
"Heather calculates ADEVs based upon the PPS and OSCillator error values reported by the unit. These values are not derived from measurements made against an independent reference (other than the GPS signal) and may not agree with ADEVs calculated by measurements against an external reference signal."
So, what are these numbers really telling me about the performance of this GPSDO? Is it really that good? If a more accurate source is not the comparison reference, what can I infer about these numbers?
I also see that LH reports that the sawtooth accuracy has improved by 20 ns. From this, I gather that LH itself is making sawtooth corrections?
mojoe:
Related to the last post, I see that the two plots (which I think are showing me oscillator tuning and PPS tuning?) are much less jumpy than before the survey. Is this due to the survey, or the fact that the oscillator is simply settling in after a few days (not counting a brief power down)?
MIS42N:
--- Quote from: mojoe on February 13, 2024, 07:35:30 pm ---Related to the last post, I see that the two plots (which I think are showing me oscillator tuning and PPS tuning?) are much less jumpy than before the survey. Is this due to the survey, or the fact that the oscillator is simply settling in after a few days (not counting a brief power down)?
--- End quote ---
I have no experience with Lady Heather, so no idea what the graphs tell you. The PPS improves after survey in, as it can now calculate corrections for ionospheric conditions etc. But it will still have a sawtooth component, due to the clock in the GPS module not being synced to anything. You will also get an improvement as an oscillator beds down, usually a slow drift in one direction which gets smaller as days go by. It is good practice to not move the GPSDO once it is running. Brief power down will have some short term effect, mainly due to the temperature of the oven dropping then going back up. Moving it can disturb the mounts, and that is a small but long lasting effect. I inverted my GPSDO once to see what effect it had, changed the control voltage by quite a bit.
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