PSN-L Email List Message
Subject: Re: Modified sound card and datalogging and geophones
From: Gordon Couger gcouger@..........
Date: Thu, 21 Jul 2005 13:52:05 -0500
> This is not earthquake recording, this is exploration
> frequencies you care about will be between 10 and 500 Hz and
> normal sound card will handle these signals. You may need
some preamps like
> you would with a dynamic phonograph cartridge, because the
> geophones are small.
> You will need zero time from your shock source (a sledge
hammer should be
> adequate). The best choice is a small, cheap crystal
> taped near the head connected to the second channel. You
don't care about
> absolute time, just time relative to the impact, so forget
I am using standard seismic sensors and I will probably use a
..22 or .38 fired
into the ground or a slide hammer lifted up by a blank
cartridge. My sledge hammer swinging days have been over for 20
years due to multiple sclerosis.
I think I need a better clock than the computer has for relative
measuring and I plan to divide down the 100 KHZ clock on the GPS
to 1000 HZ and put on each channel of the sound card for a time
base and reference. Each sensor will modulate an oscillator at a
different frequency and all will be mixed together and recorded
on the sound card and the 1000 HZ signal will be used to lock on
to decoded the others as well as a time base that is
automatically generated in the decoding process for each sensor.
There is just too much jitter in everthing I have tested in
windows to trust it to keep time even on a the sound card that
is supposed to run in real time. There also has to be some point
to referenced everthing from in both time and frequency.
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