[ct-user] RF and the DVP card

Ken Smith Ken Smith <kgsmith@onlink.net>
Fri, 16 Oct 1998 12:49:13 -0400

I am trying to solve a bad RF problem that we have when we use the DVP
cards.  (Setup is a M/S running NETTsr)

I hooked up the radio to a dummy load to keep the rf to a minimum for now.

There are a few interesting things that I found. I wired up a db 15
with only the headphone cabling in order to check that part out. I ran
the headset mic directly to the radio. First I left the plug out of
the dvp and jumpered the audio at the connector. The audio was normal
with sidetone on, and with it off there was no hint of rf in the
headphone line. I then installed the connector on the dvp card and
with the computer off there seemed to be no problem.  Results as
before when the computer was turned on there was no problem until the
dvp tsr was loaded at which time the headset audio became raspy with
the sidetone on, and with the sidetone off there was garbly pickup
(rf) in the headset.

I then removed the audio in and out lines from the connector and tied
them together. WIth the tied together lines connected to the audio in
pin 6 it was ok, but when moved to the audio out line (pin 8) the
garble returned. This would indicate that there is rf coming into the
dvp card not necessarily on the audio line but from somewhere
else. Starting the dvp tsr may turn on an analog fet switch on the
board that does something.

It would be nice to know what they are doing on the board.  We have 2
DVP cards so I tried both dvp cards and the problem is the same so it
could be computer related. (rf possibly getting into the computer
power lines?)

I tried it on both radios and on different bands with no difference.

I will test it on another computer to see if things change.  More to come.

If anyone has a schematic of the DVP card (John???), or any other
clues, it would be appreciated.

Many thanks....Ken  VA3SK

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