>
> The whip is mounted within the (classic) fin, on a ground
> plane plate; it is about 350-400 mm in front of the
dipole.
> The dipole was tested with a VSWR meter during the
> build process.
>
> My aircraft has been flying for over 4 years, without any
> reported radio problems.
First, a VSWR meter may not clearly show what that setup is
doing. It has no ability to assess whether the antenna is
capable of receiving or transmitting anything. If VSWR
reads good, we accomplish the latter by rules, like put the
antenna out in the clear as much as we can.
It looks like it's possible to violate all the rules, and
things may still work, as maybe proven here? Anyway, here
we have a 1/4-wave whip with a ground plane which isn't; it
would be better if removed. We might have no balun (ferrite
beads) on a dipole. Both coax cables run parallel and very
close to the elements. The antennas are too close to each
other. If RG-58 coax, the extra loss in the long runs of
coax is significant if the antennas are compromised.
So, to the extent the above has been working except in some
fringe situations you cited is just the enormous dynamic
range of the receivers. Antennas are reciprocal, so where
we must necessarily xmit poorly too, the receiver on the
other end has huge dynamic range also, plus rarely a
compromised antenna.
However, what happens when we play around with low RF
receive levels -- the very lowest end of this dynamic
range -- is we're asking the receiver to do things it wasn't
designed for, nor needn't be. Thus the misconception that
autosquelch must let usable signals be heard. Well, yeah.
If autosquelch trips at 5 microvolts, then two guys with
mutual 10W transmitters can talk (though weakly heard)
across 400 miles with good antennas. But similar received
microvolts within 20 miles of an airport means well, a
really, really bad antenna in a given swath in the radiation
pattern!
Reg,
Fred F.
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