What gave us a lot of trouble was the spark plug  and the spark plug
wire make a good RF transmitter.

That was getting into the trigger circuit causing havoc. This was
happening in Florida but I did not have a scope to discover it.

Henry Nee came over and made some good suggestions.

Running a separate ground wire for the power supply and the trigger
did the trick. Twisting each of them together acts like shields. I
would say this was the single biggest improvement.

Here is a video of the system working. You can see the spark plug
sparking on the middle right in the video.

The upper scope shows the spark plug wire current using a sensor
cannibalized from a Harbor Freight $33 timing light. Six sparks in a
row. The lower scope shows the clean triggers six in a row.

This system will spark near zero RPM so a wind milling prop could
restart the engine. Also despite the gear box you might be able to
hand prop.

Paul Lamar


Paul,

Glad to be able to help!

The technical reason for separating the ground wire is to separate the
signal lines from each other so magnetic field of one cannot induce
voltage spike on the other.
And having a close by ground wire provides a close by return path for
the current, which collapses the loop antenna and limits emission.
Twisting two wires together ensures that any fluctuation on the signal
wire will be counter by similar fluctuation on the ground wire, thus
getting a lean signal.

I have not built any planes yet. But I've seen some with questionable
wiring. Hope this simple rule helps everyone in the newsletter.

Henry


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