I have been watching this dsicussion with more than a passing interest.
I have 2 COM's; COM 1 is a GNS 430 connected to the standard Europa
dipole, and COM 2 is a KX125 coennected to a standard whip aerial. 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. Over the past 3/4 months I have noticed considerable
interference during reception of incoming signals on both sets,
particularly on my home frquency of 123.5. I have also noticed that
sometimes I cannot hear other aircraft talking to our tower, even though
they are quite close. I have conducted various trials with our tower,
and they cannot detect any problem with my transmissions.
On the London FIR frequencies of 124.75 and 124.6, I have no reception
problems whatsoever, except in some geographical areas, as one would
expect. I remarked to Paddy Clark (G-KIMM) at FFF that, whilst over the
North Sea recently en route to Texel, I had heard him on the FIR
frequency very loud and very clear - better than any other aircraft on
the frequency at that time - whilst he was climbing out from his base
near Bath. Looking at the chart, we were some 200 NM apart at the time.
At Oslo Guardamonen recently, I had an interesting experience. I
received taxi clearance from the GA terminal on the tower frequency
118.3, and taxied to the hold of 19R; at the hold, the tower could not
read me on either of my COM boxes, but gave me (a very distorted)
take-off clearance. As soon as I was airborne, I was given a further
clearance, which I acknowledged - to which the friendly controller
replied "Now you are loud and clear - just like reading a book!"
Back at Shobdon yesterday, I did a local trial flight to evaluate a BOSE
ANR headset (do not buy one for use in a Europa - but that is another
story!), and all the incoming signals on 123.5, on both boxes and
through both the BOSE and my usual Peltor headset, were very crackly,
but they were reading me OK.
This morning, in conversation with a professional pilot, he has
suggested that if the central core of the coax cable is connected to the
part of the dipole pointing down, that may well account for some of the
reported problems, especially when the aircraft is on the ground. I have
now looked at my build photo's, and sure enough, the central core is
connected to the lower half of the dipole.
So I have 2 problems here - maybe a problem with dipole connections, and
certainly a (separate) problem with interference on incoming signals on
2 diffrenet sets. Incidentally, my set-up works through a Garmin 340
Audio Panel.
And finally - what is a good ANR headset for use in an aircraft with a
Rotax engine - the BOSE (I have tried 2 diffrerent headsets) emphasises
the higher pitched aprt of the engine noise?
David
G-BZAM - UK 265 - 300 hrs
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