Message-ID: <5980.200002041455@gemini>
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: rsgb_lf_group@blacksheep.org
Date: Fri, 4 Feb 2000 14:56:16 +0000
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII; format=flowed
Content-Transfer-Encoding: 8bit
Subject: LF: 73kHz / Soundcards
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

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