Every ham or shortwave listener struggles with local RFI. This article kicks off a new series on how to use noise cancelers and get your spectrum back.
You turn on your radio and tune the bands. Usually, you hear some signals. But often, those signals are drowned out or hurt by local radio frequency interference. Especially, if you live in an urban neighborhood. Even with a really good antenna on a tower, local RFI is troublesome. I hear about lots of folks being tempted to just give up. My message is “not yet”. Every ham or shortwave listener should at least try using a noise canceler before packing it in. They can work surprisingly well.
More than a century ago, radio operators adopted a series of Brevity or Q Codes, shorthand ways of saying complicated things quickly in Morse Code. They are still in use. Two of the original Q Codes still in use are QRN and QRM. QRN means I am experiencing atmospheric or static interference. QRM means I am experiencing signal interference. Perhaps today we need a new code, QRFI, which means I can’t hear you through all of the local RFI.
Many Sources of Local RFI
If you want to see and hear the most frequent sources of local RFI, take a look at Sounds of RFI at the ARRL web site. For advice on how to identify and locate sources of radio frequency interference, check my video Adventures with RFI.
There is a lot you can do to clean up sources of local RFI in your own home. Most of your problems will come from switching power supplies, either AC/DC or the so called “electronic transformers” which provide AC/AC for low power lighting. Any switching power supply is essentially a free running oscillator. Often you can kill or reduce the RFI by winding ferrite chokes on the power cables. Same with birdies or radio tones coming out of your computer or network gear. But my most complex in-house RFI comes from my front-loading washer and treadmill and defies easy filtering. Fortunately, these appliances are used only occasionally.
But even if you clean up your own nest, you still get local RFI from your neighbors, often hundreds of meters away. Having a good outdoor antenna does not help, in fact it can just pick up more noise. This is where setting up a noise canceler can really help. The trick is setting up noise probes around your perimeter. More on that shortly.