RF vario interference

[ryanglover1969]

I have a little problem that has been discussed here before. Every
time I press my push to talk my vario freaks out. I have a Dittel FSG
2T radio and an LX 1600 vario. We typically fly on 123.5 or 123.3. any
Ideas on how to get rid of the interference?

Any help will be appreciated.

[Gary Emerson]

ryanglover1969 wrote:
> I have a little problem that has been discussed here before. Every
> time I press my push to talk my vario freaks out. I have a Dittel FSG
> 2T radio and an LX 1600 vario. We typically fly on 123.5 or 123.3. any
> Ideas on how to get rid of the interference?
>
> Any help will be appreciated.
Probably not RF interference, but current draw from the radio sucking
down the input voltage to the vario which makes the vario unstable. One
solution might be to put a large capacitor accross the input voltage
supply to the vario and see if that helps.

[JS]

Ferrite beads may help. Run the power and any data lines which may
go to the vario, and the power line for the radio through separate
ferrite beads, close to the instrument end of the cable. You can buy
ones which are split in two, making it easy to thread the cable
through twice then clip the two halves together and hold with cable
ties. The tubular ones are better, but it necessitates removal of the
connector from one end of the cable. You've probably seen ferrite
beads on many computer USB cables.
An (electric) ground loop cannot be ruled out. If both the radio and
vario have the -12v connected to their chassis and you have a metal
instrument panel, there is the possibility of a ground loop. Ground
loops will provide wild readings when current is drawn on the radio.
Ages ago I had a CAI audio module which had a built-in ground loop,
installed in a metal panel. One person told me to run two separate
power systems for radio and varios, and add capacitors which I thought
a bit foolish. Dave Ellis had me cut a trace on the audio's circuit
board (a prior design to Dave's involvement). This fixed the problem
immediately.
Jim