Radio transmission problems! Help please!!

[Robserve]

Hi fellow avaitors !
Picked up a snag last week, wonder if any one can help.
Radio will not transmit if i am at high revs,(3000rpm Jabi motor on Bantam).
Transmits intermittantly if I throttle back to 2400rpm, and transmit perfectly
at 2000 rpm and below.
Radio is a panel mounted Filser ATR500. Thought it may be button problem, so fitted
new one, still same.
Grounded until i resolve this, anyone help please?
Thanks, Rob .

[Stephan van Tonder]

99% of electrical problms are due to a bad earth. Start looking there.

[Rudix]

99% of electrical problms are due to a bad earth. Start looking there.

I agree with Stephan, look at the earth, could be that vibration at higher revs cause a loose or corroded connection to become intermittent. Might be worthwhile to run a temporary direct wire from the battery to the radio to see if it solves the problem.

Good luck,
Rudi

[Conrad]

yeah
Check earthing or supply to the radio in terms of clean signal. If the 12volt supply to your radio is too full of noise caused by high revs, the radio sees the supply voltage as deviating and may go lower than the supply threshold. This causes spurious reactions of the final RF transmit stage.
You can even try a fairly large capacitor as close as possible to the 12volt input of the radio.

[Robserve]

Rudi,Stephan and Conrad,
Thanks for the tips, all sounds logical. Forgot to mention that i fitted a new
battery recently, may have distubed earth cable to chassis/fuselage?
Will check all connections and let you know how i get on.
Thanks again guys ! Rob.