HXr altitude readout fluctuation with PTT radio

Post Reply
ssledge
Posts: 4
Joined: Thu Feb 17, 2022 10:49 pm

HXr altitude readout fluctuation with PTT radio

Post by ssledge »

I have an Arion Lightning I purchased recently with GRT HRx PFD and autopilot installed in 2013 at Arion Factory. Each time I push the PTT on either control stick, the altitude readout jumps into a wild descent, then a climb. I am also getting quite a bit of static on the COM with squelch off especially at altitude.

The autopilot disconnects as expected when the altimeter misbehaves.

I have attempted to modulate any RF from the alternator by placing ferrite beads around the alternator cable and battery grounds as per Clouddodger. No success, in fact, I then developed a whine in the headsets at 1600 rpm and above, so I removed them (they did not correct the apparent interference with the PTT and the altitidue readout).

Any suggestions?

Thanks,

Scott
Bobturner
Posts: 437
Joined: Mon Mar 11, 2013 6:34 pm

Re: HXr altitude readout fluctuation with PTT radio

Post by Bobturner »

Your symptoms strongly suggest you are getting a lot of RF in the cockpit from your com transmitter. Carefully check that (1) the coax connectors are properly seated at the radio and antenna, (2) the connectors themselves are properly attached to the coax, (3) antenna grounding screws are grounded, and (4) if the antenna is mounted on fiberglass that a good conducting ground plane is installed. My bet would be either the coax shield isn’t properly attached to a connector, or the connector itself has a pin that isn’t snapped into place (not full length).
ssledge
Posts: 4
Joined: Thu Feb 17, 2022 10:49 pm

Re: HXr altitude readout fluctuation with PTT radio

Post by ssledge »

Bob.
Thanks for the prompt reply. That all makes sense. Wilco.

Scott
ssledge
Posts: 4
Joined: Thu Feb 17, 2022 10:49 pm

Re: HXr altitude readout fluctuation with PTT radio

Post by ssledge »

Bob,

Sent you a PM regarding steps we have taken so far without resolution of issue. Looking for other ideas.

Scott
ssledge
Posts: 4
Joined: Thu Feb 17, 2022 10:49 pm

Re: HXr altitude readout fluctuation with PTT radio

Post by ssledge »

The solution was inline RF filter purchased from L-Com that is a 25 pin male female interface that fits between the AHRS on the floor behind the pilot seat beneath the baggage compartment. I placed it between the cable in and the AHRS unit itself. Instant solution. PTT causes now only interference with the EIS, so more filters ordered!

Scott
Bobturner
Posts: 437
Joined: Mon Mar 11, 2013 6:34 pm

Re: HXr altitude readout fluctuation with PTT radio

Post by Bobturner »

Thanks for posting. There's something to be said for being inside a metal airplane!
Post Reply