[time-nuts] advice: frequency calibration to 1 ppm possible without GPSDO?

[Alan Melia]

Mmmm well you have another uncalibrated and not very good crystal there in
the sound card, but that is not the problem.You also have some receiver
drift (Sony) I suspect at 5MHz. I would be surprised if WWV went as much as
1Hz off over a night let alone 10Hz..

Divide the 10Mhz by 2 and leak it into the receiver whilst listening to WWV
put the BFO on and you will hear a swelling bfo note. The speed of the beat
swell gives you the difference in frequency. It should be possible to adjust
the local 10MHz oscillator to 1 beat in 20 secs by this method which will
meet your criterial, without using the sound card. The Sony will probably
only be stable to about 10Hz at 5Mhz but this method doesnt require the
receiver to be stable, but you will have to play with coupling the divided
10MHz  (isnt there a WWV on 10MHz still??)

Alan G3NYK in the UK.

----- Original Message ----- 
From: "beale" <beale at bealecorner.com>
To: <time-nuts at febo.com>
Sent: Thursday, February 17, 2011 12:58 AM
Subject: [time-nuts] advice: frequency calibration to 1 ppm possible without
GPSDO?


> Hello time enthusiasts!  I'm hoping for your advice on my (perhaps modest,
by this list's standards) project.
>
> I would like to make a frequency calibration of a 10 MHz oscillator to 1
ppm (1E-6) or better, using some basic equipment. I do not have a GPSDO or
any serious lab equipment, or budget for same as this is just a personal
project. What I do have access to:
>
> 10 MHz uncalibrated TCXO     (K1602TE in 14-pin DIP can from online
auction site)
> Optoelectronics 3000A+ frequency counter   (I believe stable to < 1 ppm,
but not recently calibrated)
> Sony ICF-2010 shortwave radio   (consumer item, possibly stable at 1 ppm
level)
> Tektronix TDS220   (basic digital scope)
> Saleae Logic analyzer   (software-defined logic analyzer, the datalogger
part has generic 24 MHz xtal)
> PC running Windows XP
>
> Is it possible to calibrate my 10 MHz oscillator to some standard
reference source at the 1 ppm level using these tools?  I also have a PIC
programmer so I could construct a decade divider chain, etc. if that was
useful.  So far, directly counting the 10 MHz signal using a 10 sec gate,
the count varies about +/- 1 Hz (0.1 ppm) over several hours of measurement.
However, I don't know if the oscillator or the counter drifts more, or if
either one is close to being accurate.
>
> My first try at a standard reference was to monitor the WWV broadcast at 5
MHz, pipe the output into the PC and view it with DL4YHF "Spectrum Lab". I
found the WWV signal wandered around over 10 Hz (2 ppm) during the night and
faded at sunrise without ever stabilizing, so that doesn't seem too
encouraging.  I don't know if there are any stable signals in groundwave
range.  I've read about using an analog TV horizontal flyback signal when
locked to a network broadcast, but I'm just a bit too late for that
technique to work!  Likewise with the Loran-C receiver a guy at a local ham
club has.  I assume any accessible signals on my HDTV are internally
synthesized with dubious accuracy.  I have DSL on my phone line, but I don't
know if there's any useful standard frequencies there and I don't think I'm
supposed to directly probe the phone line anyway.
>
> Comparison to a GPS frequency standard would obviously work and since I
live in Mountain View, CA there's probably some within walking distance, but
I don't know anyone in the metrology community.
>
> Thanks for any suggestions or insights into this question!
>
> John Beale
> N8JUF
>
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