Re: [linrad] Sound card problem?

["matthieu.cabellic@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx]

Hi John

That's exactely what happens with my (not to old!) sound card. This leakage prevents you from being able to detect any weak signals close to the pitch frequency. It also increases the noise floor level leading to bad S/N even far from the pitch frequency. On my sound card it seems that there is a bad grounding design between the outputs and the microphone input. I think that such sound cards are not designed for serious dsp work but only for playing/recording music.

73
Matthieu
F4BUC

---------- Initial Header -----------

From      : owner-linrad@xxxxxxxxxxxxxxxxxxxxxx
To          : linrad <linrad@xxxxxxxxxxxxxxxxxxxxxx>
Cc          : 
Date      : Wed, 21 Jan 2004 18:51:49 -0500 (EST)
Subject : Re: [linrad] Sound card problem?


Hi Matthieu,

  One of my older sound cards has this problem (leakage from the output to
the input). Makes for some pretty wierd sounding CW when the leak freq. is
close to the real signal freq.

  regards,
  john


On Wed, 21 Jan 2004, [iso-8859-1] matthieu.cabellic@xxxxxxxxxx wrote:

> Hi
> 
> I have just Linrad 01-11 installed on my computer (Mandrake 9.2).
> I am using a Guillemot Fortissimo sound card (16bits, 16kSample/s) using just a rx channel. I use the default parameters for fft.  
> Without any microphone connected to the sound card I have this problem:
> If I increase the sound level (using the red bar) a strong spur appears on the fft display centered on the frequency of the pitch I have set. For example if I set the pitch at 600Hz and set a medium audio output level then I can see a strong spur centered on 600Hz on the fft and on the waterfall display. If I click on a frequency near the spur then the level of the spur increases but with the processing delay. 
> When I set the output audio level to the minimum, the spur diseapers.
> I think it's a problem of isolation between the input and the output of the sound card. Is anyone else have had such a problem?
> 
> Thanks your help and advises.
> 
> Matthieu
> F4BUC
> 
> 
>
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