Fri, 04 Feb 2000 11:39:15 -0500
James Moritz wrote:
> 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