Elecrafters,
I've finally licked the RFI Problem on my marine K-2 installation.
After fussing with all of the things that people suggested on the
Reflector, I blundered into the actual cause. It seemed as though it
had something to do with the microphone since I'd get RFI on transmit
when I used the mike above about 20 watts but not get it when I put the
mike down and ran TUNE up to 100 watts - must be something about the
mike.
It turned out that the problem was caused by my insufficient
modification of an Icom microphone from an M-59 which is a marine VHF
radio they make. The microphone is "permanently" wired to the M-59 but
that didn't stop me. I downloaded the schematics from the web, figured
it would work with the K2, took my retired M-59 apart so I could get at
the
attachment points for the cable and removed it where it was connected
to the main PCB.
So far so good. I correctly ascertained which lead
needed to go where, installed the 10k resistor in the pins on the K2
between +5 and the positive side of the electret element and got the
ptt function right too. Voila, it worked and worked well all the time
at 8 watts but only some of the time above 20 watts.
I just couldn't see what was making it work sometimes and inducing
huge rfi noise into my outgoing signal the rest of the time. Funny that
running TUNE at 100 watts didn't make any noise.
It turns out that the big chrome lug on the back of the Icom M59
microphone which you would normally use to hang it on a clip is wired
to the M-59 radioset with a lead running down the cable. I knew this
but since I didn't think I needed whatever functionality this provided,
didn't hook it up to the K2 - where would you?
So what was happening was that most of the time when I was
transmitting, I was holding the mike with this lug pressed against my
sweaty palm and in so doing was acting as a large 230 lb 6'3 antenna
feeding into the k2 through the lug and the wire running down the cable
closely paralelled to the rest of the lines in the cable. Apparently
other times I was holding the Mike without touching the lug which meant
I could run up to about 50 watts without a lot of noise.
So I disconnected the lead from the lug, put the mike back together and
now the rfi problem is GONE.
I'm sorry I bothered so many people with my problem. I got a lot of
good ideas
and did clean up a number of other loose ends.
Thanks for your suggestions, now to have fun with this thing as I blast
out over the water ssb at 100 watts at long last.
It's amazing how being cheap can get you an education you didn't really
want. This problem had been going on for a couple of months.
Once again, many thanks to everyone who pitched in on this situation.
73, John Ferguson KI4NGH K-2 S/N 5087
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