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PTT interference w/CHT readings

cojaken

Active Member
I have an obvious interference by activating my PTT switch causing a marked reduction in CHT readings.

Where would I start to troubleshoot?
 
These are tough to solve. Best guess is that RF from the transmitter is getting into the CHT electronics. I would start by looking for any poor/loose/corroded connections between the transmitter coax and the connectors, the antenna ground and the airframe. You might have to shield some wires going to/from the CHT electronics.
 
If your engine monitoring system is a Dynon it could very well be the EMS module. A number of years back they had some modules exhibit this issue.
 
Here's a couple of thoughts:

1. Your PTT switch ground must be the same ground potential as your audio common. Best practice is an audio ground point that is on the opposite side of the airplane from the grounding strip for your power circuits.

2) your EGT/CHT probe wires should have a dedicated firewall passthrough. They should be separate from other wiring to the extent that that is possible.
 
Check the EMS unit. If it is a SV-EMS produced by Dynon, this behavior is a known issue and only fixed by Dynon.
 
Thanks for all the input. As said the EMS is an AF3500.

I’ll get to work and let you know what I find.
 
Yes, I know this sounds crazy, but I had a similar issue years ago on my former RV-6. Thought it was a ground loop / RF combination, and don't ask how, because I don't really remember, but I cut the red "loop" wire on the alternator that was for an overvoltage light, if installed, and that eliminated the problem.....go figure....

DAR Gary
 
Two things to look at...

1. Grounding from Battery (-) -to- firewall -to- engine -to- rest of airframe/forest of tabs.

2. Positive retention, contiguous antenna terminations --There are a bunch of antennas out there that hold the center conductor in place with a washer/nut.
 
Carl - this is not a new problem. It has existed since I purchased the airplane almost 3 yrs and 200 hours ago. It's just reached the top of my list :)
 
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