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Re: [Amps] Amp causing RFI Update

Subject: Re: [Amps] Amp causing RFI Update
From: Jeff Blaine <>
Date: Tue, 4 Feb 2020 13:18:26 -0600
List-post: <>
Gary, good job there.

I find your black magic comment on the mark.  My shack is built with all the correct station engineering principles.  Antennas are nearly 300 feet out.  Single point ground into a breaker box located within feet of the shack which is also at the mains entry point to the house.  Monster ground system at the shack.  All the other stuff.

Against that I've run 4 different tube amps in that location without a single issue.  I picked up a shiny new SS amp and fried the control board in my aircon blower and high-tech thermostat working CW on 40m.  Absolute correlation between key down and smoke.

I'm sure I could have tracked down whatever was at the root cause.  I have the gear to do it.  But it was easier (and a lot more XYL friendly) to get the aircon back in action - FAST. Replaced the thermostat and the controller board.  But this time I bypassed all the I/O on the two units.  Been all quiet on the house electronics front since then.

I attribute it to RF black magic.  But I'm sure there was some RF coupling path in there somehow that the unique combination of that amp and the rest of the infrastructure brought together.  Pretty weird!


On 2/4/20 12:59 PM, Gary H wrote:
Well thanks all for the advice. As for grounds I have two 8 ft ground rods and large radial field bonded to shack ground bus with short heavy wire and connected back to mains entrance ground.

We checked both amps with a spectrum analyzer all the way to 6 GHz.  Tube amp was not real clean but within specs for a 30 year old technology. The Hercules II SS amp was very clean.  So why Hercules bother his motion light and heath does not remains a mystery.

I tried three different antennas. One coax fed dipole, one open wire fed dipole and one vertical. Only the vertical did not cause his lights to come on with either amp.  My ants are 100 feet from his motion lights and 80 ft in the air. Vert is ground mounted at radial field.

I have fixed the problem by relocating the ends of the antennas another 50 feet further away.  I not longer bother his light.  Why this happens will have to be chalked up to RF black magic and his 9.99 walmart motion lights.

Thanks all

Gary K4MT
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