Looking for suggestions on chasing interference from APRS

I now have the MicroTrack RTG unit in the wingtip. Works fine, and getting good tracks..... however,.. when unit transmits, some of my steam gage instruments swing,.. and the radio has a bit of interference. Not real bad or squeal, but probably enough to prevent clearly hearing an incoming call. (radio antenna is on top, behind canopy)

So,... looking for suggestions where to start looking, and grounding, and shielding, and filtering, and ,...


hey,...no comments about steam gages

thanks in advance

The first things I would look at:
1. I would determine that the antenna has a low vswr and all power wiring in the wing tip has seperation from the antenna and feedline.
2. If the transmit power is set to max, reduce it to around 75% (I haven't played with the RTG so not sure if you do this in software or an adjustment pot). In my old plane I had a click in my com radio when the aprs tracker beaconned - Reducing power slighlty cured the problem.

I ran both the ground and the supply line through several loops in a ferrite choke, at the wingtip location of the transmitter. I was getting a subtle dip of the altitude hold during transmit. I used two chokes, although one for both wires would probably work fine.

Are you using a J-Pole antenna for the APRS like this:
http://www.unr.edu/nevadasat/balloonsats/balloonsat pages/j_pole.html

Think so on the j-pole,....

It is a "pete howell offspring project" antenna,...

Got the same problem and haven't figured it out yet. Makes my CHTs blow out and my autopilot makes the airplane burble upwards slightly when the APRS fires. I put a ferrite bead around both wires at the unit in my wing tip. No help there.

I don't have an obvious answer for you guys. I did not take any extraordinary steps to prevent any interference on my setup.

My system is quiet and I can't even tell it is there with the old panel or the new one.

Originally when I installed it, I had both the antenna and the transmitter mounted in the wing tip. This did not cause the issues you guys are having but instead swamped the transmitter and caused it to reset over and over and over.

I moved the transmitter inside the wing and mounted it to the side of the next to last wing rib. This completely solved the issues with swamping the transmitter.

I am using a Howell J-Pole antenna that I did tune a little bit after installed with an antenna analyzer. This minimized the VSWR some.

I would make sure that the feedline is not crossing the antenna and comes of the J-pole straight back from the feed end of the antenna. You don't want the RF traveling back down the shield of the feedline. I would try putting a couple ferrite chokes on the feedline itself up near the antenna.

For those who have unsuccessfully used ferrite loops - how many times are you wrapping the wire through it? Wrap it through multiple times - maybe 10 or 20 times. Also, move the ferrite loops (on both ground and supply) inboard a bay or two in the wing from the transmitter/antenna.