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Old 03-04-2021, 06:07 PM
cojaken cojaken is offline
Join Date: Oct 2005
Location: Tulsa, OK
Posts: 76
Default PTT interference w/CHT readings

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

Where would I start to troubleshoot?
RV-9A, purchased, flying
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Old 03-04-2021, 06:12 PM
BobTurner BobTurner is offline
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,356

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.
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Old 03-04-2021, 07:17 PM
tturner tturner is offline
Join Date: Jul 2008
Location: Fayetteville, GA
Posts: 170

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.
Tommy Turner
Fayetteville GA
RV-4 sold
RV-6 sold
RV-8 Flying
RV-14A building
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Old 03-04-2021, 09:09 PM
cojaken cojaken is offline
Join Date: Oct 2005
Location: Tulsa, OK
Posts: 76

The engine monitor is an AF3500.
RV-9A, purchased, flying
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Old 03-04-2021, 09:57 PM
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N804RV N804RV is offline
Join Date: May 2013
Location: Mount Vernon, Wa
Posts: 743

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.
Ken W.
Mount Vernon, WA
2020 VAF Supporter
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Old 03-05-2021, 05:37 AM
RV6-KPTW RV6-KPTW is offline
Join Date: Oct 2014
Location: Sebastian Fl X26
Posts: 133

Check the EMS unit. If it is a SV-EMS produced by Dynon, this behavior is a known issue and only fixed by Dynon.
Dennis Callaghan (X26)
- RV14 sn:140193 - first flight 12/19/2019
- 2000+ hours on my RV6! Sold (so sad...)
- donation 12/18/2020 * 2
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Old 03-05-2021, 05:48 AM
cojaken cojaken is offline
Join Date: Oct 2005
Location: Tulsa, OK
Posts: 76

Thanks for all the input. As said the EMS is an AF3500.

Iíll get to work and let you know what I find.
RV-9A, purchased, flying
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Old 03-05-2021, 07:58 AM
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Carl Froehlich Carl Froehlich is online now
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,947

Colin - is this a new problem?

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Old 03-05-2021, 08:07 AM
calpilot calpilot is offline
Join Date: Aug 2018
Location: Independence
Posts: 109

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
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Old 03-05-2021, 08:40 AM
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bjdecker bjdecker is offline
Join Date: Jun 2005
Location: Georgetown, TX
Posts: 632

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.
Brian Decker
Retired Firmware Guy and Airplane Builder

2020 RV-14 QB -- Under construction - Tailcone & Empennage Complete.
2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned, Resurrected and flying
1998 RV-8 QB -- Started, Sold
1986 Mooney 205SE
1980 Mooney 231

Aided and abetted building a number of other RV's.
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