I missed a character, OOPS! Here is the corrected link. Sorry about that! ----- Original Message ----- From: "Richard H McCorkle" <[EMAIL PROTECTED]> To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com> Sent: Friday, August 11, 2006 10:51 AM Subject: Re: [time-nuts] How do I know my GPS stabilized oscillator is working?
> A very low cost way to test your GPSDO is to generate 1Hz from the GPSDO > with the TVB divider compare it to the GPS 1PPS with the Simple Time > Interval Counter with RS-232 > Output(http://www.piclist.com/techref/member/RHM-SSS-SC4/TIC232.htm), log the > difference readings over time on a computer, and feed the data into an Allan > deviation calculator. A true Time-Nut would use Stable32 for detailed data > analysis but at $395 this is not low cost. The free AlaVar calculator > (http://www.alamath.com/alavar.html) can remove any time offset, scale the > readings, has a built-in phase to frequency function to convert the time > data, and generates an Allan deviation chart (be sure to set Tau for the > sample period selected) that shows the stability of the GPSDO over time. > This provides a complete test system using 5-IC's for less than the cost of > the box it's mounted in. > The Simple Time Interval Counter uses a Phillips HC4046 phase detector, > a 16F688 PIC, a 16M XO, and a MAX232 for RS-232 output. The low cost XO > "dithers" the TMR1 clock to provide good averaging, but a high stability > OCXO can be used for the TMR1 clock for high accuracy testing. Insure the > TMR1 clock and the DUT are from different sources for proper averaging. > Adding an offset by inverting the DUT 1Hz to the TIC improves operation > where the inputs are closely aligned. My test box uses a 14-pin 16F630 TVB > divider with a 5M/10M frequency select pin and the arm and frequency select > pins are driven from the TIC to allow arming and frequency selection by > serial port command. An inverted 1Hz output is provided for the TIC, and a > 1PPS with 100us duration aligned with UTC provides the DUT 1PPS output. > (Thanks TVB for making this so easy!) > > ----- Original Message ----- > From: "Didier Juges" <[EMAIL PROTECTED]> > To: "Discussion of precise time and frequency measurement" > <time-nuts@febo.com> > Sent: Sunday, July 30, 2006 11:04 AM > Subject: Re: [time-nuts] How do I know my GPS stabilized oscillator is > working? > > > > Along those lines, I have a question. > > > > I am planning to (finally) finish my GPS stabilized OCXO using a Jupiter > > receiver and an HP 10811-60102 OCXO recovered from a defunct HP 8672A. > > > > The question that comes up is: how do I know my GPSDSO is working and > > how do I evaluate its stability? > > > > I understand I could measure the control voltage from the phase detector > > to the OCXO and plot it on the computer easily enough, but that will > > only tell me the error between GPS and OCXO, which can be significant in > > the short term, and that won't tell me who is right (even though in > > theory, if the OCXO is any good, it should be the GPS, then within a few > > hours or half a day, the GPS should take over). > > > > I have a Takeda Riken (Advantest) counter TR5823H that has the high > > stability oscillator option (not as good as the HP OCXO) also and Time > > Difference capability but no GPIB port, so I cannot get the output to a > > computer. If anyone has the schematics for that counter, I may be able > > to jury rig something to get the display to a computer. > > > > I have a couple of HP generators that have their own OCXO, I believe > > they are also 10811 (a HP 8673M synthesizer and a HP 3586A with high > > stability option). I also have another HP 8672A (on loan for now, but I > > can get it back if needed) and I have an EIP 371 counter with an OVENAIR > > OCXO (part number unreadable until I remove the OCXO from the chassis, > > and I do not have the spec for it). Finally, I have a Tek 494P with the > > excellent OCXO Tek has put in it (I do not know who makes it). So any of > > these instruments could be used as a reference against which I could > > measure my GPSDSO, but how do I know who is right? > > > > Aside from the fact that some instruments specify the stability in days > > and others in year does not help determine the best oscillator, which > > should I use and how should I interpret the results? For instance, is > > the Tek 494P at 1x10-7/year better than the HP 8673M at 5x10-10/day? > > Since the HP 3586 uses a 10811 OCXO at 2x10-7/year vs. 1x10-7/year for > > the Tek, it seems the Tek has better long term spec, but what does it > > mean for short term stability? > > > > Should I go out and by an HP counter with time difference and GPIB? > > > > Is there another alternative that will not require another piece of HP > > gear in my lab? > > > > Here are the specs I found for the oscillators I have: > > > > Tek 494P 1x10-7/year (after initial 6 months) > > HP 8673M 5x10-10/day (after 10 day warmup) > > HP 8672A 5x10-10/day (after 30 day !!! warmup) > > HP 3586A 2x10-7/year > > TR 5823H 5x10-8/day > > > > Thanks in advance for any suggestion or comment. > > > > Didier KO4BB > > > > _______________________________________________ > > time-nuts mailing list > > time-nuts@febo.com > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts