Message-ID: <85D78B6541034C9A9498E9191F694BD4@PcMinto>
From: Minto Witteveen <minto.witteveen@gmail.com>
To: <rsgb_lf_group@blacksheep.org>
References: <4E4527EF.2000304@iup.uni-heidelberg.de> <4E455D91.6030907@freenet.de> <4E4562C9.2050804@freenet.de>
In-Reply-To: <4E4562C9.2050804@freenet.de>
Date: Fri, 12 Aug 2011 19:54:34 +0200
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Subject: LF: Re: PA3BCA
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Hi Wolf,

I just started up my main machine – and the mail. Now the mysterious 
messaged on Speclab’s screen start to make sense J (curious how you do this, 
additional string in the http request I presume?)
I have been fiddling with the soundcard input, but I think it is ok (now). 
The digital gain is now at 75%. (mike input).
The vertical stripes you see is DCF38 splattering through the (500 Hz) 
filter of the FT817. Stefan has sent me a .USR file with filters that should 
get rid of these. Will look into this coming weekend if and when I find 
time.

Tnx.

73’s Minto pa3bca




--------------------------------------------------------------------------
Ceterum censeo Carthaginem delendam esse
-----Original Message----- 
From: wolf_dl4yhf
Sent: Friday, August 12, 2011 19:28
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: PA3BCA

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
>>
>>
>>
>
>
>
>