Home > Daily News, HF > In Search of RFI on 80 and 40m

In Search of RFI on 80 and 40m

Here at my QTH, I’ve been unable to play much radio particularly on 80m and 40m ever since I returned from my touring season- some weeks now. The problem has been excessive RFI Image

noise. Until now I’ve not been able to do much about it, as I’ve been modifying the antennas, fitting new baluns and also been tied up with fitting new security cameras to the house after an unfortunate incident.

Anyway the noise on 80m has been near S9 or greater the whole time. So where to start?


Step one was to look close to home for the source of the RFI. I started by connecting my IC703 to a battery and to my main antenna (ZS6BKW). I then turned off the main power switch to the house. Bang no noise!

OK good news I thought. That means I have some control over it, if I can find it. I then began turning on each individual circuit breaker and then checking for RFI. I starting with the big things first, hot water system, biocycle effluent treatment unit, air-conditioning, etc until I got to lighting circuit number 2- straight away there was the S9 noise. Great so all we need to do now is determine what is on lighting circuit 2 by switching off all light switches and then switching each one on, one at a time. Hang on I said, lets see if we can short cut this a bit – dangerous I know. Having worked for much of my life in technical fields doing lots of trouble shooting, particularly when with GE, I knew the dangers of abandoning the systematic approach but  Kepner and Treagoe were in my ear :-). What had changed recently? Answer- new security systems, PIR’s and cameras. Lets start there I thought. One switch I knew provided power to a PIR operated light, so I immediately turned it off- instantly there was no RFI noise! Now we are getting somewhere!

OK so I can change out the new light if necessary… but here come those Kepner and Tregoe guys again….. why does the identical light in the shed not create the same RFI?….hmmmmmm… let’s take another look at what is connected to that switch. Short cuts and assumptions can lead us up the garden path. 

Hmm it turns out there are two motion sensing security cameras fitted to the same circuit- gee I should have known that, I just fitted them the other day- I must be getting old! Let’s leave the PIR light on, but turn each camera off individually. Aha, one of the cameras is the source of the noise, one of those pesky plug packs (240V to 12V), stamped CE, but obviously not compliant. After much crawling through the ceiling space again, I changed it out for a quality unit and the noise went away.


At last no noise registering on the S meter at all on 80m, at least when using the ZS6BKW antenna. The 80m loop is a different story since it points directly at a power pole- but that’s for another blog entry another day 🙂



Categories: Daily News, HF
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