Hi If one of your sources can be offset (it's a DDS) then mixing the two is a good way to increase the resolution. Separate the two by a couple Hz and feed them into a double balanced mixer. Run the beat note into an amp and limiter. Output of the limiter drives the 5335. Resolution goes up by 10^7 if you are at 1 Hz. The gotcha is that you can't use all the resolution you gain due to noise.
The old style approach was to use a pair of OP-37 op amps, the first as a ~ 10X gain amp. The second as an inverting limiter. Simple R/C filters were used both as high pass and low pass on the signal ahead of the limiter. There is a simple / non-critical L/C filter between the mixer and the first amp. There are a number of other ways to do it. A Mini-Circuits RPD-1 makes a pretty good mixer for a simple setup. The whole thing can be done on perf board including the +/- 18V three terminal regulators. If you have a bit of this and that in your junk box, cost should be < $50. That of course assumes you already have a lab supply to drive the regulators... Bob On Aug 16, 2013, at 8:42 PM, Bob Stewart <[email protected]> wrote: > I thought I could just re-enter the numbers from the last survey I did. But > either something is wrong or I'm missing something (betting on the latter). > I can't seem to enable TRAIM. I thought I had it setup just like previously, > but under WinCore12 it simply won't turn it on. So, I'm just letting it do a > survey again, I guess. IOW, I dunno. > > > And I have a question about MATH functions on the 5335A, if you don't mind. > (I'm an HP newbie.) Is there away to use Ratio A/B and have it give a > greater resolution than a whole number, perhaps by having it average over > multiple B ticks? I think I figured out how to enter an Offset, but I just > get the ratio in single digits which doesn't really give me anything. > > > Bob > > > > >> ________________________________ >> From: Bob Camp <[email protected]> >> To: Discussion of precise time and frequency measurement >> <[email protected]> >> Sent: Friday, August 16, 2013 7:26 PM >> Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation? >> >> >> 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. >> >> >> > _______________________________________________ > 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.
