Re: RFI With KPA500 Full Output on 40m

Posted by Mike K2MK on Mar 18, 2012; 1:34pm
URL: http://elecraft.85.s1.nabble.com/RFI-With-KPA500-Full-Output-on-40m-tp7382760p7383489.html

Hi Jim,

I think it may be a fact of life with alarm systems since they have wiring all over the house. On mine, high power would signal an alarm identified as a fire alarm. I identified the wires in the alarm panel that went to the smoke detector input screw terminals and added a clamp-on ferrite core. Problem solved.

In your case you should identify the cables (probably 4 or 5 conductor) coming from the alarm keypads and clamp on a core on each one.

Anybody with an amplifier should probably have a supply of clamp on ferrite cores. Odd things start to happen as you approach legal limit. My heated matress pad would start blinking also on 40 meters. I had to use a larger diameter split core and wrap the AC power cord for the matress pad controller through it several times to solve that one.

73,
Mike K2MK

Jim Bennett wrote

Just when one thinks all is good in the world... I re-worked a Hustler 5BTV so that it covers 40-30-20-15-10 meters, rather than 80-40-20-15-10. The mod was simple - cutting off five inches from the top tube. No problem. It now has a 1.1:1 SWR across most of the bottom of 40 meters. Sweet. Kinda.

When I crank my KPA500 up to full output on 40 meters, I get RFI on my home security system. Lights up all the remote panel lights and beeps. Luckily it does NOT set off the alarm. If I back off output to 350 watts or so, no RFI problem. Both ends of my RG-8 coax have ferrite chokes. This problem ONLY happens on 40 meters; full power on any of the other bands causes no issues.

The vertical is mounted on the ground, 25 feet away from the house, with about 40 fairly short radials. The security system controller (an Ademco 4150, 21 years old) is in a metal case, and is located in a closet on the second floor of the house.

Anyone else have RFI problems with their security system? If so, how were you able to cure it? I was thinking that perhaps ferrite beads on every lead coming into the controller box may do it?

Tnx, Jim / W6JHB
Folsom CA