Hi Steve, I checked all four plugs and initially they would measure high impedance (Mega Ohms) but as I forced the fine tip of the probe through the carbon build-up they all measured slightly over 4000 Ohms, so they have not gone open-circuit but do have carbon deposits, though nothing unusual for a plug with about 50 hours operating time.  I'm not going to toss them in the garbage just yet, actually will give them a thorough cleaning and maybe try them again later - for now I'm sticking with the noise-free ones.
Jeff

-----Original Message-----
From: Jeff Whaley
Sent: August-31-20 8:14 AM
To: Rotary motors in aircraft
Subject: Re: [FlyRotary] Spark Plug SAG and Electrical Interference

Thanks Steve, so the plug itself is acting like a mini antenna ... I can easily check the resistance from end to end and measure some other plugs lying around.
Yes, there was no SAG - engine was making normal power.

Jeff,

I have gotten RF interference from resistor type spark plugs including BR10EIX when the internal resistor element fails and an arc occurs internally.  This can be verified by checking the resistance between the center electrode tip and the end where the spark plug wire attaches.  The resistance should be in the neighborhood of 5000 ohms with a good plug and infinite or open circuit on one that has failed.

My experience is that this type of failure is unrelated to SAG.

Steve Boese