I'll pop this out here to see if anyone has any good explanations for
what I experienced.
As I said in a prior post, I proudly produced my freshly aligned,
roofing-filter equipped, vintage (high serial number!), one-owner
TS-930S for a FD experience. Initial testing showed that I
experienced minimal interference from other transmitters when I was
on the CW end of 20 m and the other tx was on the phone end. In fact,
I could get within about 20 kHz of the other tx (an FT1000D while it
was running 200 W) before I heard enough phase noise to cause
trouble. Before, the '930S rx would fold if there was another local
tx on the same band. Great! Wonderful! Almost as good as my O II. I'm happy.
With that feather in my hat, I experienced one of the strangest RFI
problems I've ever encountered. The FT1000D I mentioned has an
internal PS and was in the phone position. As soon as I got the '930S
going, I noticed that I had terrible PS regulation (on transmit only,
when the PS was loaded). It was so bad that the display nearly went
out a couple of times. I also had quite a bit of hash in the rx when
the phone station was transmitting. I checked Vc and it was all over
the place, dropping to maybe 20 V or so at times.
"Great: my PS chooses FD to fail!" But then I noticed the neon
indicator lamps on some extension cords were also pulsing. A lot. And
the pulses corresponded with SSB operations. We put a DVM on the line
and measured a pretty solid 119 VAC and about 59.5 Hz line frequency,
all on generator power. We tried it with two different meters and got
the same values, though one meter could not measure the line
frequency because of RFI. We even tried it with an analog meter and
it looked OK. But those neon pilot lights kept merrily pulsing with the SSB.
On a hunch, I tried commercial power. Lo! and behold! All is perfect.
A perfect '930S PS. I put it back on generator and I had a complete
dud. What's more, if a different rig was active on SSB, I had no
problems! We carefully made a ground strap for my radio, attached
it, and found that it made no difference whatsoever (no surprise
there, but we tried it, anyway)
I zipped home, lashed together a surplus Corcom AC line filter (of
unknown characteristics) onto a spare line cord I had, dragged out a
1250 VA UPS, and headed back out. The line filter helped but didn't
eliminate the problem. I noticed that the Vc never made it to the
specified voltage and was always a bit low, but was less variable,
when the FT1000D was being used.
Then I tried the UPS and it solved everything. All was well, even
with the offending FT1000D on full boil. No other rigs seemed to have
problems with the FT1000D, but no other rigs except mine and that
FT1000D had internal power supplies. I don't know what the PSU is in
the FT1000D or even whether it's a linear or switching supply. But I
can only guess that the FT1000D dumps almost as much RF into the AC
line cord as it does into the antenna! Back in CO, where my 160 m
vertical was only about 10 ft from my operating position, at 500 W I
never had RFI to the '930S PS. This was totally strange.
Even with the UPS, I would hear hash from the FT1000D SSB while on 20
m. They could hear me, though I never affected their operations, but
the hash from the SSB was enough to wipe out some of the even
moderate CW signals on my '930S. The hash would be up to about S5 or
so and made copy very difficult -- I had to request lots of fills and
that slowed me way down.
While I was on 40 m, the SSB station complained of RFI from *me*
while on 15 m. The club has some band pass filers, so I stuck the 40
filter in and they said it was much improved. Then the 40 m filter
failed and the 15 m SSB station heard me again. I handed them a 15 m
bp filter (which should not have helped if it was a legitimate 3rd
harmonic from me) and they said all the interference from me again
went away. I still haven't figured that one out.
Has anyone ever heard of anything like this? Is there something
unique about the FT1000D power supply or the rig itself that causes
stuff like this?
Kim N5OP
|