At 10:36 AM 3/22/2007, you wrote:
>Does anyone have any experience using Isotemp 10MHz OCXO 1PPB EFC For
>GPS Discipline 12V with the SDR-1000? I see such units available on
>e-bay and they would seem to be suitable.
No reason why it wouldn't work.
You could probably not even bother GPS disciplining it, if you have a
way to keep it powered up 24/7. There's a mechanical frequency
adjust that you can use to trim it up to frequency, and the aging is
quite slow ( 1ppb/day.. 0.3 ppm/yr), especially after the first year
(0.5 ppb/day)
That way, you don't have to worry about noise on the EFC line
modulating the oscillator.
Something to think about is that the phase noise on the 10MHz source
will be multiplied up by the DDSes internal PLL, which isn't the
quietest in the world. That is, you'll get more than the 20 log(20)=
26dB increase just from the multiplication.
Just as a comparison against a quiet 10 MHz OCXO from Wenzel (Premium
10MHz Streamline). I have two kinds of Isotemp units described here,
since you didn't specify a model #.
Offset Isotemp Isotemp Wenzel
OCXO134 OCXO91 501-04609
10 Hz -105 -120 -130
100 Hz -125 -140 -155
1 kHz -140 -151 -165
James Miller's page with a disciplined oscillator shows the 134 style
of oscillator.
You can see the Isotemp 134 is about 20-30 dB worse than the $200
Wenzel. The widely available used HP10811 series OCXOs are comparable
to the Wenzel.
Some calculations I did a few years ago showed that the Valpey Fisher
200 MHz oscillator on the board has about the same close in
performance as the Wenzel multiplied up by an ideal multiplier.
So, your isotemp, when multiplied up, will be 20 dB worse than the
onboard VF 200MHz oscillator, phase noise wise.
On the other hand, if you use your isotemp as a "calibrator".. that
is, set the SDR1000 to 10 MHz-1.5 kHz, and measure the apparent
frequency of the Isotemp, you can average over, say, a second, and
get very good accuracy(essentially doing the disciplining in software).
Jim, W6RMK
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