[time-nuts] Fw: How do I know my GPS stabilized oscillator is working?

[Richard H McCorkle]

I missed a character, OOPS! Here is the corrected link. Sorry about that!

----- Original Message ----- 
From: "Richard H McCorkle" <mccorkle at ptialaska.net>
To: "Discussion of precise time and frequency measurement"
<time-nuts at 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" <didier at cox.net>
> To: "Discussion of precise time and frequency measurement"
> <time-nuts at 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
> >
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