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Date: Fri, 12 Aug 2011 19:28:41 +0200
From: wolf_dl4yhf <dl4yhf@freenet.de>
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Subject: Re: LF: PA3BCA
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Ok that reduced the soundcard gain, but what I meant was to reduce the 
analog voltage BEFORE it enters the soundcard (i.e. a real potentiometer 
between your receiver and the soundcard).

The white amplitude bar over blue background now barely exceeds 25% of 
the full-swing voltage, which leads me to the conclusion that the 
clipping happens in the analog circuitry of the soundcard, before the 
soundcard's volume control element (digitally programmable amplifier or 
something like that). So what to do:

- reduce the analog voltage * * * before * * * it enters the soundcard

- increase (!) the digital gain at the soundcard

If all works well, the amplitude bar must occasionally (during sferics 
etc) reach 100 %, which means a completely "white" amplitude bar.

I experienced the same problem with an integrated soundcard in a laptop:
The soundcard's "recording gain" was cranked down, and the full swing at 
the analog/digital converter was never reached. The best setting for the 
soundcard's rec gain is somewhere around mid-point, and input levels 
must be adjusted to a "comfortable level" for the soundcard with a good 
old "analog" potentiometer (or a fixed resistive divider, after you 
found the suitable ratio).
With about 1 Volt peak-peak (!) at the input jack (line-in), most 
soundcard should be comfortable.
If the input is not a "line-in" but a "microphone input", you will need 
much less.. just a few ten millivolts before you overdrive the card. 
And, if you overdrive the 'input stage' of the card, reducing the 
soundcard's digitally controllable gain doesn't help at all.


All the best,
    Wolf .

(PS fb copy on G3KEV's cq now)


Am 12.08.2011 19:06, schrieb wolf_dl4yhf:
> Hello Minto and Stefan,
>
> Judging from the amplitude bar on the grabber, I'd say the signal is 
> now clipped at the input to the soundcard.
> At the moment the amplitude bar appears solid white, regardless of the 
> presence of a carrier on 137.7 kHz.
>
> Oh... now (19:05 dutch local time) it looks better.
>
> Good luck testing.
>
> 73,  Wolf  DL4YHF .
>
> Am 12.08.2011 15:17, schrieb Stefan Schäfer:
>> Hi Minto,
>>
>> http://pa3bca.pa3bca.nl:8181/
>> Tnx for the grabber. It seems to be very sensitive now!!! Just 
>> starting to do new tests here.
>> Yesterday my FT14-77 became very warm, acting as a common mode choke 
>> in the mains line to the PA. Now replaced by a massive toroid (blue 
>> color high mu material) and bigger cable :-) Small 0,25 sqmm cable 
>> smelled in the antenna feed cable...
>>
>> 73, Stefan/DK7FC
>>
>>
>>
>
>
>
>