>> * It seems to me we could minimize this problem by writing a small
>> program that would tune an over-the-air frequency standard (like one
>> of the WWV broadcasts) and compare it to the local oscillator. The
>> resulting frequency offset could then be stored as a default setting
>> for subsequent GNU Radio runs, so that e.g. if your program asked to
>> tune to 250.000 MHz and the USRP's LO was slow by 50 kHz (0.050 MHz)
>> then internally it would know to tune to 250.050 which is probably
>> closer to where the real signal will be. Of course the LO would shift
>> slightly based on temperature, but if you measured and stored the
>> value after warm-up, it would probably be relatively stable.
>>
>> John
>>
>>
> Probably reasonable as a first-order approach. That assumes that
> frequency errors are more-or-less linear.
> Further, you want to store the result as a PPM estimate, rather than an
> absolute frequency offset. For some
> cards, the difference won't matter, but for something like the WBX, with
> a very-wideband synthesizer, it
> does matter.
>
> FM radio stations also tend to use very-high-quality LOs for their
> transmitters, although the wideband nature of their
> signal makes it somewhat awkward to do fine tweaking. Hmmm, I wonder
> about the audio carrier of a TV signal, that
> might also be reasonably stable.
I haven't used it, but kalibrate [1] seems to do what we're all talking
about, using GSM base station clocks (that are required to have an
accuracy of 50 parts per billion). Maybe see what that code is all about?
[1] http://thre.at/kalibrate
--
Patrick Yeon
ThinkRF
613-369-5104 x418
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