Ray Allen aileron and elevator trim LED woes & RF Interference

Just when we thought we were done wiring our RV9A, we noted the Ray Allen aileron and elevator trim LEDs would go bonkers when we pressed PTT on the Garmin SL30 or the ICOM A200 radio. As you'd speak into the mic the LEDs would bounce back and forth.

A 50 ohm dummy load on the antenna stopped the signal from interfering with the LEDs so we knew that RF was the culprit and the radiation was not coming from the radios or antenna lead cables.

We tried installing capacitors across the sensor lines to remedy. No luck. Ferrite cores placed around the sensor lines with three turns yielded no improvement. We also yanked the airplane outside the shop to make sure the signals were not bouncing back from the walls. I was ready to bounce off the walls, but not the signal.


A call to Ray Allen yielded no help.

Finally, my good friend Chet replaced the sensor line wiring with shielded cable. Problem solved.

My thanks to Gil Alexander, Mel and especially Chet.

Barry
Tucson

When you say "replaced sensor line", do you mean you replaced the Ray Allen indicator wiring with shielded wiring? Also, which antenna are you using?

Barry,
Thanks for the insight.

I'd like to know what type of sensor wiring you were using at first.

I have the 5 wire twisted cable from Spruce. I have not installed yet, so I want to be sure this is not what you had trouble with.

From the Aircraft Spruce catalog:
WC2 5-WIRE
This durable, flexible wire cable is highly recommended for Ray Allen installations. Consists of 5 separate color coded, 26-gage, 19-strand, silver-plated, FEP Teflon? insulated wires inside a tough, all Teflon? sheathing.

It is twisted and I would hope the twisting would not allow it to do what you've experienced.

Thanks,
Mark

Take two aspirin and call me in the a.m.

tkirk said:

When you say "replaced sensor line", do you mean you replaced the Ray Allen indicator wiring with shielded wiring? Also, which antenna are you using?

Click to expand...

Give us a call in the morning at 520-797-0265 after 8am Tucson time (same as California). Chet will be there and will be happy to answer your questions.

After all the pain we endured, it would be unfair to not help someone else.

Barry

Weird -- mine did that inside the hangar (all metal) but is fine outdoors.

Sensor wire?

Barry,

What is the "sensor wire"? Is this the wiring from the servo to the indicator?

Paul

Questions Answered

The original wires were single conductor #22 gauge. Five wires were used, two for the motor and three for the position sensor. The #22 wires were spliced to the #26 wires at the servo. The wires then ran in a bundle from the Aileron servo mounted according to Van's plans to an indicator mounted in the lower left corner of the instrument panel.
Shielded two conductor and three conductor #22 gauge wire was used as it was available. I prefer to use #22 gauge as it is easier to work with and more durable then #26. Also seperating the motor from the servo eliminates the possibility of motor noise interference.
A DB9 connector was used at the panel to allow easy disconnect. The wire shields were soldered to the DB9 case to provide grounding at the indicator.
This provide an easy fix to a frustrating noise problem.


Starbird

MrNomad said:

Just when we thought we were done wiring our RV9A, we noted the Ray Allen aileron and elevator trim LEDs would go bonkers when we pressed PTT on the Garmin SL30 or the ICOM A200 radio. As you'd speak into the mic the LEDs would bounce back and forth.

A 50 ohm dummy load on the antenna stopped the signal from interfering with the LEDs so we knew that RF was the culprit and the radiation was not coming from the radios or antenna lead cables.

We tried installing capacitors across the sensor lines to remedy. No luck. Ferrite cores placed around the sensor lines with three turns yielded no improvement. We also yanked the airplane outside the shop to make sure the signals were not bouncing back from the walls. I was ready to bounce off the walls, but not the signal.


A call to Ray Allen yielded no help.

Finally, my good friend Chet replaced the sensor line wiring with shielded cable. Problem solved.

My thanks to Gil Alexander, Mel and especially Chet.

Barry
Tucson

Click to expand...

Here's another suggestion... What type of coax did you use for your comm antenna? And how did you ground your Comm antenna (if at all).

While, what you did with solve the problem for your trim indicators, you still have an RF problem that is allowing stray RF to ride on the outside of the sheild of your coax on your comm antenna. That is most likely getting into lots of other things that just aren't showing up yet.

Remedies, include using good RG-400 coax, Amp or Amphenol crimp style coax connectors (for the type of coax that you are using). Throw away and RG-58 you might have been tempted to use or the Radio Shack connectors that don't have good isolation from tip to shield. And lastly assuming you may have done the above things already, changing the length of that coax slightly (maybe by a a foot or 2 one way or the other).

Just a few more random ideas for the next time.