[Kenwood] ts850 rf feedback

Sun, 04 Aug 2002 17:13:06 +0000

Bob

I had this problem with both my 850, 870 and my 950. when used with the 
PK232 ......some observations

1) It doesn't matter what mic you use ( It  happens with the MC-60, Heil 
Boom  and Heil Gold Line)
2) I was never really convinced that it is RF in nature as no end of RF 
chokes, etc were able to cure it. Rather I suspect some kind of digital 
hash or impedance mismatch as a result of having both the PK232 and the mic 
essentially BOTH hooked up in parallel, possibly even some kind of 
relatively high frequency audio feedback or oscillation.

I have since sold my PK232 as most if not all of the digital modes can be 
generated with computer sound cards these days so I don't really have a way 
to experiment further anymore.
Suggestions
1) Put an audio isolation transformer between the PK232 and the input to 
the TS-850 (Radio Slock sells them for a few bucks).
2) Put a small switch or relay in series with the PK232 line ( which is 
what I did) open the line up when you are not using the Pk232

Dave
NR1DX (ex K9NX, N7EX and N0DH)

At 09:39 AM 8/4/02 -0400, [email protected] wrote:
>I am using a TS850 MC60 mike and PK232MBX for rtty.  With the cable plugged
>into the TS850 acc2 jack from the TNC, there is rf feedback when trying to
>use the mike on ssb.  The only cure to use ssb is to unplug the cable from
>acc2.  I tried ferrite beads and shielding on the cable to no avail.  When I
>qso VK4SJ and mentioned the rf feedback problem she asked if I were using a
>TS850 and a MC60 mike before she knew my setup - it must be a common problem!
>  She said the only cure was to throw away the MC60 mike.  Without the rtty
>cable plugged in, the TS850 audio quality is outstanding and I very often
>receive comments on how good it is.  I looked in the service manual and it
>appears that the TS850 already has adequate bypass capacitors on the acc2
>connections.  I looked in the Kenwood archives and didnt see any discussion
>of this problem.  Is there any cure other than unplugging the cable or
>throwing the mike away?  73 Bob W7LR in MT          [email protected]
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Dave
NR1DX
[email protected]

"A man who picks a cat up by the tail learns a lesson he can learn no other 
way" .... Mark Twain