LX5000/AR4201 interference

[Flavio Formosa]

I have a very strange interference problem with my
LX5000 and Becker AR4201 radio: when I transmit, the
LX5000 changes pages, menus and inputs on its own.
The funny thing is that if I hold the PTT and keep
silent, nothing happens: problems come when I start
modulating (talking).
The wiring has been double checked and found ok.
The two instruments are placed very close together,
with the LX directly above the radio, and virtually
no space in between.
The panel is carbon fibre.
The microphone is of the panel mount type, but insulated
from the panel surface.
LX Navigation could not find a solution so far.
A friend suggested I wrap the LX in a fine brass mesh
and connect this to GND (to shield it from electromagnetic
interference), but I am unsure.

Any competent suggestions?
Thank you,
cheers

Flavio

[COLIN LAMB]

The Becker transmitter is probably transmitting properly. The problem is
that the LX5000 is acting as a receiver and when you transmit you cause the
interference. Such interference is not uncommon among electronic devices.

You LX5000 is not supposed to be a receiver, but transistors and diodes can
act as a crystal radio receiver and develop voltage when you transmit. In
this case, the audio "demodulated" by the diode rectifier (or transistor or
ic acting as a diode) is developing the voltage and causes the interference.

What you need to do is to prevent the transmitted signal from getting into
the receiver.

This is often a "keep working at it until it stops" approach. Start with
using shielded wires for each of the leads of the LX5000. Then, add ferrite
beads (can be clip on type available from Radio Shack) over each of the
wires as they come into the LX5000.

If that does not work, shield the leads also to the Becker - in particular
the supply line and headset.

If none of that corrects the problem, then the LX5000 could be picking up
directly from the Becker antenna - which means that the Becker antenna must
be shielded from the LX5000 and/or a greater distance created by moving the
antenna (possibly to the tail).

Persistence, perserverence and an occasional beer (not before flights)
should get it solved.

Colin