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 <[email protected]> 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 <[email protected]> >> To: Discussion of precise time and frequency measurement >> <[email protected]> >> 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 <[email protected]> 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.
