[Kenwood] TS950SDX RFI Issues

[Bill Smith]

----- Original Message ----- 
From: Brad Johnson
To: kenwood at mailman.qth.net
Sent: Wednesday, January 05, 2005 2:54 AM
Subject: [Kenwood] TS950SDX RFI Issues


Hello all.

I've posted this in a few places hoping that someone might be familiar with
the phenomenon, have an explanation, or know of a fix....

I am having some odd issues with my TS950SDX.

Your problems are not with the TS-950.

The  first oddity occurred when I connected a W2IHY equalizer. There was a
"proximity issue"...the only solution to which was to move the eq several
feet from the radio. It was a very low level hum that seemed to have its
origins in the radio, rather than the mic, cable, or eq. All of the usual
"fixes" didn't improve it. I was
able to reduce it enough that I forgot about it.

Sounds like the W2IHY equalizer is picking up hum from the TS-950's power
transformer.  Likely the W2IHY has transformers in it, and they are picking
up the 60-hz magnetic field from the TS-950.  Solution is to move the EQ
away from the TS-950, out of the magnetic field.

Hum pickup can also be be caused by RFI, particularly through the power
cabling.


I did make one interesting
discovery though....with the rig in TX, and a mic connected, if you tap on
the mic connector with your finger or pencil, you can hear it through the
audio chain...almost as if you were tapping on a live mic. I have called
this phenomenon "microphonics" in the past...not sure if that is the correct
term.

It is "microphonics" and a possible indication of a poor connection
somewhere or a defective component.


Having run mostly non-resonant antennas and parallel feed lines into the
shack, I am no stranger to RFI, particularly when I started running a small
amplifier. In the course of experimenting with different mic, tuner,
antenna, grounding scenarios with the 950, I discovered that it appears to
be unusually susceptible to RFI.

Or a poor ground.

 When I switch to the TS2000, connect the
same mic, the same amplifier, use the same tuner settings, and the same
antenna...my audio is clean, even with the processor on (which I never use).
The same operating conditions produces noticeable RFI in the 950's
audio...and turning on the processor results in.... well...you can imagine.

RFI

I made another interesting discovery.... with NO microphone attached to the
950, RFI can be introduced into the audio chain by turning on the processor
and turning it up. Perhaps this is not as unusual as I think it is...?

The processor has inherently high gain, hense the increased sensitivity to
RFI.  This is not peculiar to the 950.

I was able to reduce, but not completely eliminate RFI by disconnecting the
950 from the station ground buss and inserting an MFJ artificial ground
connected to a 135 foot counterpoise.

That is a dead giveaway that your RF ground is not working.  You are
establishing a better ground reference with the MFJ and counterpoise.

 Of course operating the 950 into a
dummy load or resonant antenna eliminates the RFI issue.

Same issue.  RF currents are flowing through your grounding system.

Ideally all antennas used would be resonant ones, but that isn't always
achievable. I
have been looking around and have not found any mention of unusual
sensitivity to RFI being a well known quirk of the 950.

Your grounding system apparently needs work.  Can't blame the radio.


I have heard that there may be something "unusual" about the mic amp circuit
in the 950...that it might not be at the same ground potential as the
chassis? Given the odd behavior I have observed, I am wondering if this
might not be the case...or perhaps there has been a component failure or
poor connection in that section?

Don't know about the microphonic connnector, although that could simply be
an artifact of your RF problem.  You apparently don't have a good station
ground and RF is getting back into the 950.  It could be coming in through
the power line, on the coax shield, through the mic connector or any other
connection you have made to the transceiver.  Try winding the power line and
other connections through ferrite cores (located as close to the transceiver
as possible).

First check the ground and make sure it is what you think it is.  Unbalanced
antennas require a superior ground.  You might try an antenna tuner and
unbalanced to balanced balun at the end of a coax run to isolate RF currents
from the transceiver, but you'll still need a good ground reference at the
antenna.

73 de Bill, AB6MT
billsmith at ispwest.com

Thanks,

Brad Johnson  AA5CH
http://aa5ch.smugmug.com/

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