From: DL4YHF@aol.com
Message-ID: <33.12a9e073.27f3a01d@aol.com>
Date: Wed, 28 Mar 2001 15:14:21 EST
Subject: RE: LF: <Tech>Re: A Question
To: rsgb_lf_group@blacksheep.org
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<HTML><FONT FACE=arial,helvetica><FONT  SIZE=2>Hi Alberto, Jim, and LF group,
<BR>
<BR>As Jim already wrote, the amplitude measuring facility of Spectrum Lab uses a 
<BR>more or less arbitrarily chosen scale which is 0 dB for the lowest possible 
<BR>signal which can be detected (with a 16 bit ADC). However, I am not very 
<BR>happy with that choice myself. There is also the possibility of using Andy's 
<BR>CFAR noise detection algorithm (it is hidden somewhere in the spectrum alert 
<BR>function, works perfect except for the case when there is no input signal at 
<BR>all ;-).
<BR>
<BR>Someone (was it Alberto ?) has already written about the problem that some 
<BR>soundcards seem to use a kind of AGC (no matter what the mixer settings say), 
<BR>&nbsp;making absolute measurements inaccurate in the presence of static crashes 
<BR>etc.
<BR>
<BR>IMO, a good solution is to display the difference (in dB) from the 'cursor 
<BR>position' to a definable 'reference area' where either the noise level or the 
<BR>amlitude of a reference generator can be measured. An optional "smoothing" 
<BR>(or averaging) of the displayed dB value can also help.
<BR>
<BR>Alberto, if you find a good solution for this I would like to know how it 
<BR>works. Thanks...
<BR>
<BR>Good luck for now,
<BR>73s Wolf (DL4YHF).
<BR></FONT></HTML>