DVP Card Hum Problem Summary

Rod Greene w7zrc@micron.net
Fri, 2 Feb 96 20:53 MST

Sorry this took so long, but I had hoped to find a solution and post the
No luck this time.. But thanks to all who sent messages and offered suggestions.

-------Summary of responses to "DVP Card Problem at W7ZRC"----------

There were many helpful responses. Here's a summary with lots of good
suggestions. I wish one of them had fixed my problem. Any one want to
purchase my card for a nominal fee?   ;)


This sounds like the same problem WR3E had a while back.  He had an early
cable assembly with a metal hooded connector.  When we swapped it out, the
problem disappeared (his was a Kenwood cable I believe).  It was not a really
loud hum, but certainly annoying.  K1EA replaced it and it's working fine now.
(This was a brand new DVP and cable that he had let sit around a while before
installing).  73, Tyler KF3P

I once had an OMNI6 & found it very poor in regard to EMC.  Take a look at
the schematics & look what little they do on external connections to keep
crap out.  When it came to the mic, the problem is aggravated by a high
impedance (50k, I think) input - to get _anything_ to work required going
through an isolation transformer.
73, VS6BrettGraham aka VR2BG bagraham@hk.super.net

Hi Rod.

Try lifting one of the shields/grounds on one end of the
audio cables. I don't have a K1EA spcl, but use a SB Pro
card and a small TSR to play msgs, called CVB. Interface
was built my me and I spent many hrs debugging it in this
hostile RF enriched environment. 73 & GL de Walt - K2WK

K1VR replies:

	The last thing you want to do is take engineering advice from a
lawyer, but here's a solution to a Kenwood hum problem which plagued me
for YEARS.

	In the Kenwood world, there is a difference between chassis ground
and microphone audio ground.  Make sure you separate the two.  I didn't
know there was a difference, and had people complain to me forever, until
K2WR told me about this.  If this isn't your problem, at least I was 
trying to be helpful. 
                      Fred Hopengarten K1VR

I have the same problem with my TS 940.  When the DVP cable from the computer
is connected to the radio's front panel mic connector, I get the buzz/tone in
the headset.  The buzz/tone is not AF or RF gain control dependant.  When the
DVP cable is removed, the buzz/tone goes away.  Even if the computer is turned
off, the buzz/tone persists.  I've even disconnected the DVP cable from the
computer, with only the loose open ended cable connected to the radio, and the
buzz/tone is still there.

I thought it was just this one 940 that had the problem, since I connected a
different 940 and it didn't seem to have the problem.    

Any suggestions????

73 James/kd1ng ..    >>  setzler@c813.npt.nuwc.navy.mil  <<   
From: KWIDELITZ@delphi.com on Wed, Nov 29, 1995 6:03 PM
Subject: Buzz from DVP
To: ct-user@ve7tcp.ampr.org

I've got a buzz in my headset that goes away when I take the DVP out of the
headset line. The buzz is there even when the computer and radios are turned
off. Any ideas for a solution (capacitor across the line?)


I have one that I believe is the same rev level as yours, bought about the
same time.  It is clean as can be.  Either you've got a malfunction or,
possibly, it's the same thing that happened to me one time, only my hum was
in the RX audio.  Turned out to be the connector on the back of the DVP, not
tight enough, or else the DVP itself, not solidly enough seated in the bus.
Try both cuz I can't remember which it was.  You might also look at whether
your motherboard is making good contact to the case of your PC -- sometimes
they forget to scrape the paint away where the ground bus contacts the case.

GL -- the DVP is a good thing.
73, Pete Smith N4ZR


Here's a summary of what I tried (with no luck) at W7ZRC


1. Not connecting the chassis ground at either end of the cable or both
   ends. Made sure the chassis ground cable and the mic return were not 
   connected, then
2. Connecting chassis ground and audio return together, then to
   the chassis at either end of the cable or both ends
3. Double and triple checked all wiring connections to the plugs and
   jacks. Rewired most of it just in case
4. Made a bare minimum cable consisting of only the mic audio and mic 
   return (2 wires)
5. Put .o1 caps in series with both the mic audio and/or the mic return
6. Checked the AC mains to make sure the ground, neutral and hot were 
   wired correctly
7. Isolated the computer from the AC main with a constant voltage 
8. Rewired my station ground system: Three 8 ft ground rods each spaced
   two feet apart and within 4-6 ft of the rigs. Then running a braided 
   copper ground strap (5/8 in) between the station ground, rig and 
9. Examined the card itself closely and checked to make sure the ground
   traces were solid and connected to the PC's bus connector pin. Checked
   the PC bus ground pin to make sure it connected to the PC chassis.
10.Checked the PC power supply to make sure the AC connector ground pin
   made connection with the PC chassis.

I'm still open for suggestions and comments. If there are questions, please
reply directly.  73, Rod

w7zrc@micron.net             Rod Greene W7ZRC             Boise ID    DN13UN

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