Angel and others having this problem,

I have noticed this problem with some motherboards. This happens on newer
motherboards that have switching power supplies that place a lot of high
frequency noise onto the + and/or - 12 volt supply lines. This noise gets
into the multiplexor chip and op-amp on the A/D card.

About two months ago I started adding two inductors to my A/D card that
filters out the problem. The modifications are easy too make, but require
some soldering skills. I will create a web page that documents the changes
needed to add the inductors if anyone wants to modify their board. Just
about any small inductor will work as long as the DC resistance is only a
few ohms. If you don't have a supply of inductors at hand I can send you
two if you send me 
an envelope with return postage.

If your not into soldering you can send me your A/D board and I will make
the modifications for free. All I ask is enough money for return postage.

Too see if you are having this problem do the following using SDR.
Disconnect the 37 pin connector and press the "1" key and then the "C" key.
After a few seconds note the minimum / maximum counts from the A/D
converter. If you have a 16 bit A/D chip and the min/max count is greater
then +-8 the modification may help. With a 12 bit A/D chip the min/max
counts should'nt be higher then +-2.

-Larry Cochrane
Redwood City, PSN

At 11:44 PM 7/4/00 -0500, Angel wrote:
>
>Hi,
>
>I just got me new computer and much to my chagrin now all four of the
>traces on SDR are much noisier.  Little spikes, jus ta few counts.  When I
turn off the
>new computer the noise goes away and when turn it on the noise comes
>back.  Obviously one solution is to not turn on the computer.  Are there
>any others?
>
>
>Best regards,
> Angel                            mailto:angel@............
>
>
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