I'll figure out something. I'm thinking of icing down my DDS device to put it at a known temperature so I can do drift comparisons. If not that, there'll be something else I can try.
On another note: I thought I had destroyed everything when I swapped the UT+ back into the GPSDO. Fortunately it was just that the UT+ needed to be reset, and I had destroyed a USB-TTL adapter and not my new little Adafruit. I'm going to have to figure out exactly what command sequence needs to be sent to the UT+ to get the comms working again and write a short program to do it. For some reason the WinCore12 program wasn't able to bring it up. Bob >________________________________ > From: Angus <[email protected]> >To: Discussion of precise time and frequency measurement <[email protected]> >Sent: Friday, August 16, 2013 6:14 PM >Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation? > > >Hi, > >To be able to test GPSDO's (and GPS in general) was one of the main reasons >that I made a temp controlled chassis for an LPRO and gave it air pressure >compensation. That was good for tau's of hundreds to tens of thousands of >seconds, and even longer with drift compensation. Add in a clean-up oscillator >if desired, and you have a pretty good reference. > >Incidentally, I tested 2 FEI5680A's, a Temex LPFRS and 3 LPRO's in this type >of setup, but only the LPRO's allowed the air pressure effects to be almost >completely cancelled out. For some reason the others did not react to >fluctuating air pressure as predictably. > >Angus. > >From: "Bob Camp" >To: "Discussion of precise time and frequency measurement" >Sent: August 16, 2013 7:45 PM >Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation? > >Hi > >With the 5335 you have a measurement with dead time. That makes things a bit >hard to figure out. A much better way to go is to feed a pair of 1 pps signals >into the 5335 and measure their time difference. Unless they are quite close, >you can go for a while with no ambiguity to the reading. The effective >resolution increases linearly with the time length of the observation. There >also are a number of very nice programs that will let you collect the data >from the 5335 via GPIB. > >Assuming your 5335 works like mine does it's got about a 1 ns resolution at 1 >second. It'll give you 1 ppb at a 1 second gate and 1 ppt at a 1,000 second >gate. By the time it gets to 1,000 seconds the internal counters have >overflowed and the reading is a bit messed up. > >Without some sort of accurate reference, there's really no way to know for >sure what's going on with a GPSDO. One solution is to build two or three of >them and watch them fight with each other. Another solution is to pick up a >Hydrogen Maser. It's always a "what's in your wallet" sort of decision. > >Bob > >On Aug 16, 2013, at 2:26 PM, Bob Stewart wrote: > >> Hi again Bob, >> >> D'oh, I think I totally misunderstood your figures in my first response. >> The .16ppb is not the frequency accuracy of my GPSDO. It's the amount that >> I'm moving the OCXO during a 5 minute timeframe, which is something else >> entirely. Like I said I do not have a known good oscillator to compare to. >> However, I have a DDS oscillator I made some time ago, and it seems to be >> pretty stable if I let it be. So, what I've done is to hook the GPSDO to >> the clock input of my 5335A. I've then adjusted the DDS so that it reads >> near 10.000000 MHz, and watched it over a round-trip 5 minute period several >> times with a large enough gate that I get 8 decimal points on the counter. >> I don't see any relationship between the few milli-Hz movement the counter >> shows and the changes to the DAC. During several runs last night, I saw >> less than 30 mHz of movement, which, if true, would be 3E-9, or 3ppb, right? >> Or would that be +/- 1.5ppb? >> >> Bob >> >> >> >> >> >>> ________________________________ >>> From: Bob Camp >>> To: Discussion of precise time and frequency measurement >>> Sent: Friday, August 16, 2013 10:47 AM >>> Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation? >>> >>> >>> Hi >>> >>> Ok, let's try some math and see if I can do it without blinking this time…. >>> >>> +/-4 Hz for 6 volts is 0.66 Hz / V >>> output is 10 MHz so 1 Hz is 0.1 ppm >>> your OCXO is running at 0.066 ppm / V >>> That's also 66 ppb / V >>> >>> 0.02 V at 66 ppb / V is 0.0132 ppb or 13.2 ppt >>> >>> The UT+ has a sawtooth output that's about 45 ns >>> That's 45 ppb at one second >>> >>> 5 minutes is 300 seconds >>> >>> so 45 / 300 = 0.15 ppb or 150 ppt >>> >>> If it's the later clone version it might be about 1/2 of that. >>> >>> Are you doing sawtooth correction? >>> >>> Bob >>> >>> On Aug 16, 2013, at 11:09 AM, Bob Stewart wrote: >>> >>>> I'm converting the code for the VE2ZAZ FLL to a PLL. I'm seeing the phase >>>> correction change the EFC up and down about .02V to .03V over a period of >>>> 5 minutes or so (it varies). The full range on the OCXO is about +/- 4Hz >>>> varied by 0 to +6V, so at least this is a tiny value. I feel pretty >>>> confident with my code at this point. I'm using a Trimble 34310-T OCXO >>>> for which I've been able to find almost no information. Could this >>>> oscillating phase correction be some sort of thermal oscillation? I've >>>> tried two separate 34310s and both act more or less the same. My GPS >>>> device is normally a UT+, but I just now swapped in an "Adafruit Ultimate >>>> GPS Breakout" to the same effect. Is this good, bad, or indifferent for a >>>> GPSDO? I started this project not knowing what to expect, and I still >>>> don't. Experienced help, speculation, or even just kind words at this >>>> point would be appreciated! =) I don't have a known good/stable >>>> reference to compare >> this >>>> to. >>>> >>>> Bob - AE6RV >>>> _______________________________________________ >>>> time-nuts mailing list -- [email protected] >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >>> >>> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > >_______________________________________________ >time-nuts mailing list -- [email protected] >To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. >_______________________________________________ >time-nuts mailing list -- [email protected] >To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
