COM interference from Trim Servo (G3X based)

[lr172]

I have recently noticed some COM interference while changing pitch trim. In the 10, you need a lot of pitch trim once the final flaps come down and it is making the calls from the tower hard to hear while on final. I have only noticed this in the pattern and it is intermittent.

I have the G3X AP servos and the trim wiring runs through them. I know they use PWM, but this is occurring at speeds where the servo should be delivering 100% trim power. Don't know if that servo still uses a PWM signal at 100%, but guessing it is not. 100% trim power should be constant 12v with no modulation.

The wire from the servo to the trim motor is not shielded, but it is pretty far from the avionics and antenna and assumed it was far enough away to not cause problems.

Wondering if others have had similar problems and what the resolution was.

[g3xpert]

Originally Posted by lr172

I have recently noticed some COM interference while changing pitch trim. In the 10, you need a lot of pitch trim once the final flaps come down and it is making the calls from the tower hard to hear while on final. I have only noticed this in the pattern and it is intermittent.

I have the G3X AP servos and the trim wiring runs through them. I know they use PWM, but this is occurring at speeds where the servo should be delivering 100% trim power. Don't know if that servo still uses a PWM signal at 100%, but guessing it is not. 100% trim power should be constant 12v with no modulation.

The wire from the servo to the trim motor is not shielded, but it is pretty far from the avionics and antenna and assumed it was far enough away to not cause problems.

Wondering if others have had similar problems and what the resolution was.

This problem is usually seen in composite aircraft as it is challenging to ground the shield of the connection between the GSA 28 and the trim motor, on the trim motor side, although there are ways to work around that. When using Speed Scheduled trim, it is always using PWM, even when below the lower end of your airspeed schedule. We recommend wiring the trim motor to the GSA 28 as shown in the manual for this one, shield the wiring and ground the shield as outlined in the wiring diagram.



Thanks,

Justin