Re: 73kHz Sideband noises / Soundcards
Dear LF Group,
I quite agree with Alan that measuring noise levels using a
soundcard is unlikely to result in a definitive measurement, but in
the few minutes available it was that or nothing. The point was that
the Rugby transmitter definitely has significant levels of noise
sidebands due to power supply ripple, and that it is quite feasible
that these are responsible for the noises we hear.
A noise level -45dB relative to the carrier, within a few 100Hz of
the carrier is probably pretty good performance, or at least not a
major fault - after all, there is bound to be some ripple, and -45dB
would correspond to only1% or so voltage ripple. Most amateur
transmitters are probably not as good as this, but are unlikely to be
a problem, since the ERPs involved are of the order of a million
times smaller - I estimate the ERP of my 73kHz signal is a
whopping 5 - 10mW!
Since soundcards and software like Spectrogram have many other
uses to radio amateurs apart from reading QRSS, it would be
interesting to know if any data exists about the dynamic range &
spurious responses of the soundcard/software combination - does
anyone have any information?
I expect to be adding my own contribution to the 73kHz noise level
this evening from about 20.00 onwards - hope to see you there?
Cheers, Jim Moritz
73 de M0BMU
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