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Old 09-15-2021, 07:28 AM
Tcheairs Tcheairs is offline
Join Date: Feb 2021
Location: Covington
Posts: 106
Default RF Interference RV&A?

I had posted some time ago that I had started having problems with my Garmin 430W radio transmissions interrupting power to my AP-74 autopilot and my Dynon D-100 EMS. Also, when transmitting on my #2 radio which is a Garmin SK 40 interrupts power to my Garmin 430w causing it to reboot from scratch. My Dynon D-180 EFIS is NOT affected (thank goodness) by radio transmissions.

So, I am suspecting RF interference issues. I do not recall these issues happening before I had a GDL-82 installed for ADSB compliance. Has anyone else experienced this issue? And what did you do to solve the problem? Could it simply be a matter of shared common grounds? Routing of the GDL-82 Coax?

Thanks in advance for comments..

Last edited by Tcheairs : 09-15-2021 at 07:45 AM.
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Old 09-15-2021, 07:51 AM
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Walt Walt is online now
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 6,290

Sounds like the increased current flow from transmitting is creating a low voltage situation which will cause things to reboot.
Power supply/connections and grounds is the first place to start looking, or just low battery voltage/bad alternator perhaps?
Walt Aronow, DFW, TX (52F)

EXP Aircraft Services LLC
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Old 09-15-2021, 08:33 AM
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bjdecker bjdecker is offline
Join Date: Jun 2005
Location: Georgetown, TX
Posts: 892

What's changed?

First - Understand & document the electrical architecture of your aircraft:

1. 14v or 28v.
2. 1, 2 or More Batteries.
3. 1, 2 or More Alternators, Internal or External Regulation
4. 1, 2 or more busses (Main, Essential, Aux, etc. etc.)
5. Ground strategy - airframe, common point (array of tabs), or mixture

Measure voltage at different points in the systems and during different modes of operation. Typically, with engine running and alternator engaged, bus volts should measure in the 13.8Vdc - 14.2Vdc range.

I suspect, as Walt also suggested, that you are experiencing an increase in current draw on the radio(s) which is causing the supply bus voltage to drop
below the design limits for the device.

Why? Could be bad grounds (corrosion, loose wire, undersized ground wire, etc.) or perhaps it's a failed antenna connection, excessive VSWR bleeding RF energy everywhere...but...probably not.

Waiting for more data...
Brian Decker
RV-7 (Flying)
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Old 09-15-2021, 08:53 AM
Tcheairs Tcheairs is offline
Join Date: Feb 2021
Location: Covington
Posts: 106

I am not the builder of this Vans. But I do have the electrical schematics of the build and will get into them.

To answer your questions: What I do know is that it is a 12V system, one internally regulated belt driven alternator, 2 12v batteries (Odyssey), a main and essential bus, capability of supplying power to main bus via standby battery.

Thanks to your advice, it seems to me the first step is to check the voltage drop on the bus when transmitting along with checking the output of the alternator. Hopefully it is a voltage problem rather than wiring or RF interference.

Thanks for suggesting a starting place.
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Old 09-15-2021, 09:36 AM
Bo1000 Bo1000 is offline
Join Date: Nov 2013
Location: Austin
Posts: 38
Default Agree with Walt, Brian - brownouts


To rule out RF: see if keying up the SL-40 will reboot the 430W with the other loads turned off. If not, the problem is not RF. Do this with the plane on the ground please.

A marginal battery could also cause a brownout, but I suspect a battery in that shape would make the plane impossible to start.

A poor connection (ground or power) could reveal itself when a transmitter (current hog) is keyed, especially if any of the connections are daisy-chained.

Trying to monitor a brownout event, if that's what this is, might be tricky - might only last milliseconds.

(Does anyone make/have ribbon cables and a breakout box that would allow the 430W or SL-40 to be operated and tested, say, while sitting on the glareshield? While on separate wires to the battery? Surely Garmin repair stations have this.)
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Old 09-15-2021, 10:16 AM
Tcheairs Tcheairs is offline
Join Date: Feb 2021
Location: Covington
Posts: 106

Sounds like a good troubleshooting scheme..Could do the same thing with the garmin 430 and the EMS..Thanks for the suggestion. I'll try it and report back
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