DJA,
"> ######Just to throw a spanner into the works here - I have an
interference problem with my engine monitor. When I transmit, I get spurious
readings. I have tried to shield, but one interesting thing must be noted. I
tried my hand held radio in the cockpit and I get the same effect on the
monitor (although not as pronounced - lower transmit strength). This
eliminates any possibility that I have a problem with my antenna cables in
the airplane. The RF energy is getting into the system somehow. RIght now,
this is low on my priority list and the long term solution may be to ignore
the engine readings when i transmit!"
Quite right. It's perfectly true that transmission power can upset delicate
detectors, and some manufacturers make them far too sensitive without regard
to protective circuits - it's cheaper. The early Korean 2-head VCRs are a
perfect example.
However, it's also true that a one-watt handheld at one foot is
just as powerful as an 10-watt inbuilt, when the latter's antenna is four
feet away. Something about the inverse square of the distance. There is a
limit to practicality.
Tracing the leads to eliminate proximity might be useful.
Locating the antenna well back in the fuselage likewise. But I still say the
vast majority of problems has been solved by securing the connectors - in my
40 years anyway. The twin Comanche doesn't really matter as far as OAT goes,
but a sharp left bank is much more critical.
A careful ham in Essex was driven off the air by neighbours even
when he proved his transmission were squeaky clean. But he persisted and in
the course of his long search, he discovered a rusted windowsill in his
neighbour's greenhouse formed a diode junction at a very sensitive
frequency. It was rebroadcasting his emissions. Only after he proved the
case (it took police to force the neigbour to allow the test) and a year's
wait for rectification, was he able to continue transmitting. Sometimes it's
a third party.........
It doesn't hurt to examine the connectors annually though.
Good luck,
Ferg
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