Fergus Kyle wrote:
> ...but RF feedback may also be present. The latter is less
> likely with transistors than with tubes....
I agree it could be RF pickup and a 1st guess at that. But bipolar transistors
can do pretty good job of "rectification" with 10W coming out of an antenna
6 feet away from whatever is picking it up. That's about 3+ volts of
electromagnetic field at that distance, and unlike metal airplanes, the RF
energy inside the fuselage of a plastic airplane is as strong as it is outside.
Worse yet, you might agree Ferg, is that at VHF comm frequencies, there's
the "near-field effect" within about 8 feet from the antenna, meaning
whatever is picking it up need not be of a much of a tuned element to cause
bad things. If able to move the antenna, it may not take much, as near
field attenuates with the cube of the distance.
No one has specifically mentioned that the mic audio wires - ground + hot -
should be inside a shield which is grounded at the radio end.
Paul, RF pickup can be determined by severely attenuating the output from
the antenna, by several methods, if you'll repost the need to do so as last
resort.
Reg,
Fred F.
N3EU
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