From: "Stephen Izett stephen.izett@gmail.com" <flyrotary@lancaironline.net>
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Subject: Gremlin Search
Message-Id: <85D1B6AB-1D86-4867-94EE-AFFF01BA8E48@gmail.com>
Date: Mon, 6 Jan 2020 10:20:12 +0800
To: Rotary motors in aircraft <flyrotary@lancaironline.net>

Hi Guys

I wonder if you guys have come across this fault or can help with my =
search for the culprit.
Having made some alterations to our Dynon Skyview EFIS we went to fly =
only to have a problem and so aborted the flight.
Previously the engine has been rock solid with none of the new symptoms.
I have an Electronics/Communication systems background.

The problem/symptoms:
	1. During taxiing we noticed that every time we keyed the mic of =
the Garmin GTR225 we experienced significant mixture variations and =
stumbling of the Engine (Renesis 4 Port - EC2)
	2. We then sought to clearly establish the symptoms and =
discovered that along with the very repeatable interference to the =
Engine/EC2, the Skyview EFIS was also effected by tx. The vertical speed =
would go +250ft/min then -100ft/min on keying the mic.

The changes we had made:
	1. Changed the Pitch Autopilot Servo to a heavier duty unit (no =
wiring change)
	2. Installed the Dynon Auto Pilot & Knob Panels - this meant a =
new connection to the the Skyview bus and shifting the trim control =
(inputs from sticks, Power and output to Electric Trim motor) from a =
relay deck to the Dynon AP Panel (Build in trim controller).

My thoughts are two fold:
1. RF getting into somewhere it shouldn=E2=80=99t. No changes have been =
made to the antenna or feed. However, I may have shifted some cables in =
close proximity to the antenna coax. I had just washed and left wet the =
Glasair's (fibreglass) vertical fin which has the 1/4 wave dipole =
antenna inside of it.
2. Earthing issues. There were no changes to the Earth system.

Path forward:
1. Replace antenna feed with dummy load to isolate RF while still =
drawing current from the GTR225. (Where to borrow a dummy load around =
here?)
2. Check wiring to see if it is apparent that some have shifted in =
relationship to the antenna coax.
3. Check Earth buss for good connections.

I do recall hearing someone with a similar fault on an EC2/3 years ago.

Would really appreciate your feedback. I have little experience with RF =
interference and its rectification(no pun intended).=20

Sincerely

Steve Izett
Perth Western Australia - Glasair Super IIRG - Renesis 4 Port EC2 EM3 =
RD1C