"Jeff Liebermann" wrote in message
...


I had a weird problem related to unused equipment. There was an
unused "smog alert" receiver at one site, connected to an external
ground plane antenna half way up the tower. It was turned off as the
system was obsolete. Someone noticed that if they unplugged the
antenna connector, some of the intermod would magically disappear.

Such is the case on USN ships of my acquaintance. If the ship buys a
commercial transceiver and throws the antenna any old place, the front
end becomes a mixer. There's a reason why (most) military gear is
pricey. It's been engineered not to do that.

Aside:
It's not always an active device that causes problems. I had one ship
that was getting massive interference on UHF comm circuits between
about 325 MHz to 399 MHz. from a radar operating around 430 MHz.
Normally not a problem. The cause was a tangled hunk of wire I
found in the field of the radar. It had been used to secure scaffolding
during the ship's previous inport period.

Every time the radar lit up that bailing wire, the resulting arcing
and sparkling generated broadband RF pulses at the radar's rep rate.

I was climbing around on the mast, looking for just something of the
sort. When I saw that wire, I actually spoke out loud to it.

I said, "Well, hello there!" True story.

It's one of several reasons we preached "Topside Housekeeping"
to our Sailors during ship visits. Leave nothing on the mast that
doesn't have to be there.

"Sal"