Mike Tope wrote:
> Has anyone compiled composite noise test data on various
> radios at larger frequency offsets? I think ARRL test reports
> go to +20KHz maximum. You really need to see whateen the
> noise spectrum look like at 50 to 500 KHz to make intelligent
> decisions about which radios are good for this sort of
> environment.
I've been thinking about this, and it's sort of non-trivial.. We've got a
bunch of different rigs and amps at the club stations we could measure.
We've got spectrum analyzers and measurement receivers (although, I'm not
sure my measurement receiver goes down to HF.. might only go down to 45
MHz). I think it might take a bit of work to look for 80+ dB sidebands. We
might need to build some filters to notch the carrier, and then carefully
measure them, and then work that into the measurement.
Another approach would be to use a high purity signal generator to null the
carrier (zero beat it). I've played a bit with trying this in a different
context, and the close in phase noise makes it a challenge (the carrier
wanders a few Hz over a few seconds time frame), but it might work. You
could digitize a bunch and then post process it.
This is an interesting problem. We do phase noise measurements all the time
(and, in fact, next week that's exactly what I'm going to be doing) for tens
of Hz to hundreds of kHz away for microwave sources at 8GHz, and we're
measuring 100 dB or so down. The test sets have a PLL with a very quiet VCO
that tracks the carrier, and then you look at the PLL beat against the
input. The resulting measurement is the combination of the VCO noise from
the PLL and the UUT.
Has anyone seen anything like this published before?
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|