EGT's jump when transmitting

Something interesting was observed yesterday. While flying the EGT's would jump 200 degrees whenever the transmit button was pushed.
I could not replicate it on the ground with the engine off.

Anyone else seen this?

Not too surprising, seems like something on mine goes nuts when transmitting also. The fix is easy - don't look at it when transmitting... Or put a choke on the sensor lines near the engine monitor, might fix it depending on where the rf is getting in.

Sounds like a grounding problem.

Page 2-2 of the FlightDEK-D180 Installation Guide says,
"Because of the current drawn by the FlightDEK-D180, even very small resistances between battery ground and instrument ground can cause voltage differences which adversely affect engine sensor readings. An easy way to test the quality of the instrument?s ground is to measure voltage between the ground pin at the FlightDEK-D180 and the ground lead at your aircraft?s battery. With the FlightDEK-D180 powered on, connect one lead of your voltmeter to a free ground lead coming from the FlightDEK-D180. Connect the other lead of your voltmeter to the ground terminal of your battery. The voltage between these two points should measure very close to 0 mV (within 5 mV). If it does not, you must improve the ground connection between the ground of your battery and that of your avionics bus."

In the above test, the D-180 case can be used in leu of a ground lead.
Make sure that the battery cable is well grounded to the airframe at the battery box.
Make sure that the control board is well grounded to the airframe with a wire and screw per the plans.
Make sure that the Dynon D-180 is well grounded to the airframe.
There should not be any paint on aluminum at the ground connections.
An additional grounding wire could be added to the D-180 EMS 37-pin connector at location 3 or 5 or 13 if desired.
Joe Gores

Antenna Ground

In addition to the checks Joe recommended: I would ensure the antenna base is securely attached and is making sound electrical contact with the airframe. Otherwise, RF energy will travel along and radiate from the outer conductor of the antenna cable and could couple to other things. Routing antenna cables away from mic, sensor,and power wires would be a good practice too, but I know in our 12's its pretty much just one big bundle. Let us know what you find.

Here is a reply from Dynon, they say there working on it.

"Reply #18 - Apr 19th, 2012 at 6:13pm

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Dynon Technical Support

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As we said, we do expect to have a way to mitigate this soon. We'll keep you posted when we have an update. Until then, know that there's no damage being done, and when you're of the PTT button, the readings are accurate.

Thanks

Thanks for the reply. Glad they know about it and are working on it.
I sure like the system.

Its not a new problem

My 1992 Masten digital engine monitor goes haywire high CHT and EGT when I transmit, and my buddy's Insight GEM-700 in his Bonanza does the exact same thing too.

Mine is OK

I checked mine while flying this morning and saw no change in the EGT while transmitting, intercom, or anything else.

Wayne 143WM

Mine does the same thing, only about 150 degrees.

Doug Dahl

My EGTs jump when transmitting, but only since I changed to the Skyview system. Notice the varying magnitudes of the jump depending upon what frequency you're transmitting on. The RF from the radio is what's causing it and no amount of shielding is going to alleviate it. Believe me, I've tried.

I had an RV-6 some years ago that demonstrated the same behavior. I've just learned to ignore it because it does not harm.

As noted in an earlier thread, EGT's on a 12 serve no purpose. You can't use them to lean the mixture and any spark plug fouling is only going to raise it 50 degrees or so. Spark plugs are so cheap, you can virtually change them every time you take the cowl off. Now CHT readings are important and can be a sign of a suffering engine. If they're good, you're fine. Remember Dynon sells their equip to planes that can make use of an EGT. They're useless on the 12.

Pete