430 transmit causing erratic instrument readings?

I have a 430 wired with RG4 via one bulkhead connector and then on to an Archer wigtip antenna. Upon transmit, all of my resistive circuit instruments go crazy including CHT, EGT, flap indicator, etc..

The wiring of the wingtip antenna tested properly. Installing a temporary antenna and holding it up by the flywheel during transmit reduced the problem. Ferrite filters did not improve the situation.

Is there some type of local shielding behind the panel that can be done?

Other suggestions?

Thanks,

Dave

I just went through this. Are you transmitting inside a building, surrounded by lots of metal shop equimpent and tool boxes?

First thing to check are grounds. Once you've eliminated the possibility of bad grounds from instruments or radio, then the cause could be RF bounce. Tossed around on various threads here, I've heard that you need to be outdoors and 50 feet away from the nearest building before you can eliminate bounce as a factor.

Another thing to look for is ground plane on the antenna.

I have a RAMI bent whip antenna with a BNC connector. To get it to work right in a temporary setting, I had to use two 22" strips of aluminum at 90 degrees clamped to the antenna base near the cable. That gave me the ground plane I needed and seriously mitigated the stray RF, even inside the shop.

Some considerations

First off, as suggested, this problem is exasperated by the feedback enviornment. Make sure you are out of the hangar. Even the ground can contribute. My antenae is on the belly and flaps down makes a difference.

Beyond that, Check all of your coax connections, particularly on the back of the transmitter.

There are many threads dealing with this. Search em out for more good info from guys who really know this problem.

Good luck.

What test would determine if it is the ground issue or feedback?

I have tested the airplane pretty near the 50' you specified but, still had the problem.

For example, is there a similar signal I could generate and see similar impact on instruments. (confirming the rf feedback source)

Or, is there some evidence of a grounding issue I can test for?

i used a bulkhead connector from B and C. i dont recall them being fully isolated from the skin. Could they contribute?

thanks for your help....