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.
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