Hi Also remember - you need to do a survey on the UT+ and put it into position hold / timing mode. If you don't you can add a bit more to your error budget.
Bob On Aug 16, 2013, at 7:58 PM, Bob Stewart <[email protected]> wrote: > 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. _______________________________________________ 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.
