Kim,
Yes I have heard of similar problems from a nearby rig, and offer some
suggestions on things you tried and what could have helped you did not know.
First for all to know, using Astron external power supplies, it is often
helpful to twist no. 12 stranded power supply DC leads all the way to
the rig being powered. Next, for any power supply, put a disc ceramic
by pass cap big enough to be low impedance (reactance) at 75m and up on
the DC terminals.
The 1000's internal supply probably had a cap, but it might have gone
open, or they relied on a big electrolytic which can be bad at RF
frequencies for bypassing. A Corcom on the 1000's AC power input would
keep stuff off the line, unless it is conducted on its chassis to the
third pin ground lead of AC distribution. Also, make sure the AC cord
and distribution back to you was not a quarter wave total length at your
band, or their band (20m). Quarter waves will be high impedance usually
at the end that is closest to your having interference.
It was good you tried a Corcom on your AC input, but both places would
have been better. The reason the UPS helped is that every AC
transformer you add adds about 20 dB RF attenuation at HF. That I
learned in the RFI business and confirmed by measurement at 160m one time.
Yes, each station using bandpass filters helps the other stations
nearby. Despite the filters being bandpass at a certain band, they may
have some out of band responses, but your using a band pass probably
attenuated your third harmonics if yours. But maybe the third harmonic
was generated in their rig input, or its tuner if external, and adding
the 15m band pass filter cut down the rig input level to where the
fundamental could not generate the third harmonic in some non linear
junction at their rig.
You also could have had an RF detector and re-emitter in a bad joint
forming a diode and radiating a third harmonic from impinging
fundamental from you. Not your fault at all. Could have been in
someone's antenna connection not your own!
We have often used big Corcom or other brand AC line filters to sort out
noise on AC lines in shipyards, or aboard ship in a drydock. The best
are ex submarine RTTY AC line filters from 1968 vintage submarines.
Found that out when some became surplus while we were down the docks
working an RFI problem aboard Enterprise. It is good to meet and know
the Chief of the Electronics shop! Or any Chief Petty Officer, when you
are a Navy contractor as we were! They can get things down! "How many
filters do you want, here, take a few extra" was the response to my
request for "A filter". Those became a standard accessory to our
instrumentation for shipboard work.
Now, on general FD RF problems I will share my 2012 repeat of a 1980
problem, and the solutions we used. First of all I had a 20m phone
station in the same room at next desk, to a 20m digital and CW
station.Both 100 watts. I had a Kenwood TS 450.
The Icom 756 the CW man had, would cause overload and hash if we got too
close to his frequency. Sometimes, even up the phone band, I would
cause some hash to him, on an apparent spurious receiver mixer response
he had. He was running a vertical at the end of 270 feet of double
shielded coax, and a remote controlled SGC tuner, 270 feet from the rig.
(Yes that is longer than the 75 foot cable supplied for ICOM tuning, but
we put an extension cable in use). Within 20 feet of the CW station was
our phone doublet, and 88 foot one inverted Vee style, with center at 20
feet, and ends at about 15 feet. It was parallel to the table upon the
which the rigs sat. There was a large patio door with aluminum rim and
frame between the antennas and the rigs. We had double shielded coax
for about 20 feet and then 30 feet of RG 8x.
Now, at a certain point in the FD, I was getting funny tuner settings,
and was not getting out when calling S9 or higher level stations.
The rig I was using was a Kenwood 450 with an external Dentron Super
Tuner. The tuner has an aluminum case as does the Kenwood, and they
were side by side, and by that time, we had moved them closer and turned
the Kenwood a bit closer on one end to better see its display. I
switched antennas, and still had problems, so suddenly, I remembered FD
1980, when I had a different rig and a compact B&W 300 watt rated, tee
tuner. That year, I had first sat the tuner on top of the rig being
used, and not getting out like this time.
Moving the rig and tuner apart cured the feedback, which is what is was,
and it was by magnetic coupling as best we could tell. Again, in 1980,
aluminum tuner case, and small spacing of coil from the bottom cover of
the case, right above the rig.
So close they had added a piece of mu metal as a magnetic shield under
the end of the vertical coil. Now the Super Dentron has no mu metal
shields, but with its larger coil has ample ability to couple fields,
and I surmise, I got too close to the Kenwood and caused coupling. This
probably caused some ALC detection and folded back the power.
Moving them apart 5 inches cured the problem and immediately the next
strong station I called came right back to me, and the next, and the next!
It was so dramatic, I wanted to share this RFI cause with the group.
Also, on a 1990's FD, we had the experience with a Ten Tec Scout, of RF
feedback, incidentally with the same tuner, the Dentron. That one had
two causes, we found a bad thread on a UHF connector and changed it, and
we had a bad shield connection in the jumper coax from rig to tuner.
There is my Ten Tec content!
73,
Stuart Rohre
K5KVH
(operated W5KA 3A)
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