[1000mp] 1000 MV RFI Discussion

Mon, 28 Oct 2002 06:21:57 -0800 (PST)

I feed all my wire arrays with balanced line, but one
of my antennas is an off-center fed 475' zepp so the
feedline does radiate some. Or a lot?

On 10m at high power (1500W) it will reset the
processor in my Mark V - it converts to 7.000MHz just
like yours and you lose the memories. I went through a
step-by-step analysis of the problem by disconnecting
*everything* that connects to the radio and then
re-connecting them one by one.

Results:
Both key jacks (front and rear) are quite 
susceptible to RFI. I wrapped the key leads four times
around a Radio Shack ferrite clamp - problem solved...
for a week. When it rains, the effective electrical
length of the feedline shifts and the node was back
near the shack! Now I have ferrite clamps on the
microphone input and the CAT port input and especially
the amplifier T/R relay drive cable - problem gone. I
also opto-coupled my computer keying lines to break
that ground to the computer and put a ferrite clamp on
the LPT1 port to keep the computer happy.

To be fair, the computer's UPS had trouble on 10m,
too, so there was quite a bit of RF in the shack. I
moved the tuner about 15' away from the station and
ran coax to it, the RFI went down a lot - it was
radiation from the feedline being inside the shack,
not bad isolation from my balun.

I have since changed to a monobander yagi for 10m
(also fed with balanced line but, well, BALANCED this
time) so probably I can remove these things, but they
stay for extra measure.

If you are end-feeding a long wire that runs directly
into your shack, there is a lot of RF in your shack.
This radio is the most susceptible to RF in the shack
of any radio I've ever had but the ferrite clamp fix
works, even at 1500W.

If you are stuck with the LW and your radio resets at
only 200W then you should probably change the length
of your wire some -- is it only on one band? Then
change the length of your wire for sure. What is your
ground radial system like? If your 'ground' is the
house wiring then this will make it worse, too.
Perhaps moving the feedpoint outside some and running
a short piece of high quality coax to your indoor
tuner would help or moving the tuner to a remote spot
and motorizing your L and C (seriously, I've done this
and it's super cool)?

Radio Shack sells two ferrite clamps, a circular one
designed to fit over round cables and a square one
that opens so you can wind multiple turns around the
core before closing it. You may find the circular one
is best for your mic cord, I did.

One day I'll take this radio apart and put internal
ferrite beads INSIDE so it's bulletproof. ONE day I'll
clean the gutters, too!

73, Steve N4SL Machias, WA CN88xa

--- Chuck Wells <[email protected]> wrote:
> Thanks for the help with the tuning problem!! RF in
> the shack makes perfect
> since.
> 
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of
> Chuck Wells
> Sent: Sunday, October 27, 2002 12:34 PM
> To: [email protected]
> Subject: [1000mp] RE: 1000 MV Tuning Problem
> 
> 
> 
> Hello,
> I had a General license friend visit my shack today
> to test drive my new
> Mark V. When we tried to tune-up on 10 meters
> antenna B (long wire) the
> radio switches to 7.000.00 ant position A. It will
> tune normally on all the
> other bands. Lowering the power setting does not
> make any difference.
> Anybody had this happen? Thank for any help.
> Chuck/KG6JYK
> 
> 
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