Jeff,
I have a Bob Archer antenna in the tail of my Europa. My trim control &
Navaids go nuts when I transmit and I haven't ever solved the problem. My
SWR is spot on, and the I never have a problem being heard, so the
transmitter is working well.
I am about to go down the ferrite bead route as well, I would be interested
to know how you get on.
Paul
---> I've had a bit of experience with RF problems, being a ham operator for the
past decade or so, both with a 5 watt 144MHz handheld and also a 150 watt SSB
HF radio. The wierd part is the 5 watt radio caused more issues than the big
rig. I could wipe out every TV in our house with it.
The problem is not with the transmitter, or the SWR of the antenna. The problem
is with other wiring, like the trim servo leads, picking up the radiated power
and bringing it back to whatever is there. The solid state components in the
'box' act like a diode rectifier (a.k.a. crystal radio) and that power just
overloads the circuitry. Most solid state electronics today is pretty well wide
open to RF interferrence. Telephones are usually really bad, TV's, alarm
systems, touch lamps, etc. are great at getting RF into them.
Part of the problem is the Europa itself. Since it's glass, the fuselage offers
no internal shielding of other equipment from the radio transmissions like a
Spam Can would.
The other problem is that any leads to servos, lighting, etc. will pick up the
transmitted power, and be especially bad if the lead lengths are a multiple of
the frequency (in 1/4 wavelengths).
A few solutions to try:
1) Make sure the radio chassis is grounded well to the airframe ground bus.
2) Make sure you are using good coax for the antenna lead (double shielded if
necessary
- foil and braid)
3) Get a ferrite bead assortment (Amidon is one brand). The ferrites do NOT go
on the radio, but on everything else that is affected. This would mean that
signal and power leads to trim systems, engine monitors, etc. all need to have
beads or torroids applied.
4) In worst case situations, you need to actually shield the affected equipment
itself, which means building a grounded box around the device from copper sheet,
etc.
Chris
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