Hi Markus,
Since I also "suffer" from insufficient bandwidth for a link to my
remote receiving site:
What about converting the signal down to 'easily managable audio
frequency' (low enough for yet another narrow-band FM link), using
a 32.768 kHz 'clock' crystal for the mixer ? With reasonable
pre-filtering the image frequency won't hurt much, and even a
Gilbert cell mixer (NE/SA612) may get the job done quickly. Not
sure if the frequency stability will be good enough for uHz
resolution, but considering that in the days of IBM PC XT / AT the
system time drift was low (and very predictable), it may work.
73,
Wolf DL4YHF .
Am 03.03.2014 18:51, schrieb Markus Vester:
Bob,
nothing
at all in Nuernberg last night. There seemed to be no diurnal
change in the background noise level, showing that my receiving
setup is not sensitive enough yet. Apparently the current LF-VLF
diplexer arrangement is too lossy for direct connection to the
soundcard, and in addition the ADC noisefloor is a bit higher
above 24 kHz (Sigma-Delta noise shaping?). Will try to redesign
the circuit and insert a simple preamp tonight.
I
have also slowed the grabber window to 424uHz bins, hoping for
more long carrier transmissions tonight.
Best
73,
Markus
(DF6NM)
