Content-Transfer-Encoding: 8bit
Message-ID: <3.0.1.16.20020319120232.3127297c@pb623250.kuleuven.be>
Date: Tue, 19 Mar 2002 12:02:32
To: rsgb_lf_group@blacksheep.org
From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>
Subject: Re: LF: Soundcard Mods
In-reply-to: <7D653C9C42F5D411A27C00508BF8803DCB9A09@pdw-mail-r1.dstl.go v.uk>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

Hello Andy,

if you (your company) can spend some dimes on it I would strongly recommend
to use a good ADC card. There is a lot of plug-in cards available, but we
tend to use Keithley cards. For a recent project I used one of their
top-level cards that included a high quality 16-bit / 100kHz ADC (and
furthersome DAC, accurate timing control etc.), it costed somewhere arround
1700 Euro. If you are satisfied with lower sample rates (40kHz or so)
prices go down to 650 Euro.
It is probably possible to do some changes on a soundcard board to get it
stable at a convenient clockrate, but if you count all the hours of work it
might end up more expensive ...
Also be aware that a soundcard has capacitive input coupling (I measured
the -3dB point at 30Hz once), so low frequencies / slow changes will be
distorted.
Bypassing the input caps doesn't work as it causes the DC offset to go crazy.

73, Rik  ON7YD

At 09:59 19/03/02 -0000, you wrote:
>Has anyone tried changing the clock source on a Soundcard for a different
>frequency ?  For a  job here at work we need to sample more accurately than
>the usual crystal oscillator (does this sound familiar ?) and at different
>sampling rates.  It would be ideal if we could push it to 50kHz, but 25kHz
>and 12.5kHz would do, as well as accurate 8 and 16kHz options.  One idea
>that immediately comes to mind is to remove the Soundcard clock crystal and
>feed in the input from a synthesizer.  Before diving inside a PC, I wonder
>if anyone has ever tried this ?  Modifying the integrated soundcard on the
>Dell machines here could prove a bit tricky just to try on spec.
>
>For LF use, how about an externally derived 1kHz sampling rate for input
>from receivers using a narrow CW filter and BFO pitch set below 400 Hz ?
>
>Andy  G4JNT - but with another hot on now.
>
>
>-- 
>The Information contained in this E-Mail and any subsequent correspondence
>is private and is intended solely for the intended recipient(s).
>For those other than the recipient any disclosure, copying, distribution, 
>or any action taken or omitted to be taken in reliance on such information is
>prohibited and may be unlawful.
>
>