What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Intermittent Tx

RV12Nut

I'm New Here
My radio transmits on-off-..-on constantly once I'm a good ways down the runway and while in the air. If I remain on the ground, this behavior doesn't show up.

This failure appeared slowly; when I first noticed it, I could fly for about an hour and the onset would be slowly at first until it became constant. That delay has disappeared entirely. Now it's as soon as I'm airborne.

The behavior does not appear during a run-up to 4000 rpm. I would think that if it was vibration related, that might do it. Nope.

I had thought it was a failed PTT. Replacing one didn't seem to help. I had both sets of audio-jacks tightened too.

I didn't build this RV12, so I have that handicap.

Some suggestions I've had so far is that it might be airflow-related movement interfering with a ground.

Has anyone seen something like this? Any suggestions on where to start? This makes my radio effectively useless.
 
The radio is transmitting (as in you get a TX light or such), or is this just your intercom picking up from the air noise?

Carl
 
Transmit

I had a similar issue on our 8. Turned out to be a cold solder joint on the rear stick PTT female side connector. The rear stick is removable so there is a connector on the airframe side. Drove me crazy until I finally found it by turning on the aircraft Comm, transmitting, listening on a handheld radio and jiggling every wire I could find. It acted exactly like a stuck mic.
 
where to start

Is this intermittent tx occurring when you are pressing the PTT button? Or does it occur without pressing the button at all?
What type of radio is installed?

I would start by checking all the wiring connectors that carry the PTT signal, this includes the microphone jacks, stick PTT, intercom if there is one, interconnect board, back of the radio.

Then also check what PTT signal is getting to the radio by measuring resistance across the relevant pins at the radio connector. If the PTT pin is at gnd this tells the radio to transmit.
 
This occurs without touching the PTT at all. It's hard to reproduce as it no longer happens on the ground after I replaced the pilot side PTT button that was clearly faulty.
 
I get a Tx light that flashes on and off. It's transmitting, as it causes havoc with the runway lights if I were to leave it on. (I've turned to a hand-held while I search for the cause.)
 
Last edited:
Did you get a wiring schematic with the plane?
The PTT is usually at the end of that circuit. You will have to follow it all the way back to the radio, or intercom, than radio if you have that setup. Also if your passenger side also has a PTT, you would do the same there.
Somewhere the PTT wires are grounding. No quick or easy way to sort it out but by tracing those circuits through.
 
check wires at stick base

One easy check is to visually inspect the PTT wires where they come out at the base of each stick, under the boot. If the insulation has chafed off the wire in this area, which is subject to movement, then that could be one possible source of the short. I'm assuming this is how your aircraft's PTT wires have been routed.
 
Yesterday I pulled out the seats and disconnected one, then both of the PTT wires (by disconnecting the non-grounded wire).

I was hoping to isolate the issue by removing variables.

Neither worked. It still transmits repeatedly upon rotation.

I also did a second run-up to full power while on the ground. It did not recreate the "flickering Tx" issue.
 
Last edited:
simulate flying attitude

Another suggestion to try and identify the cause: what happens if the nose is raised e.g. by pushing down on the tailcone while on the ground? Maybe bounce up and down a bit also, to simulate rotation and flight? I'm guessing that vibration and/or G load is causing movement in a loose joint or cable. If you can somehow reproduce the problem on the ground it will be easier to trace.
 
Back
Top