Choosing a radio for remote operation
RFI Hunters II – Preparing for the Hunt

RFI Hunters

RFI Hunters – this should be the name of a new TV reality show featuring people carrying strange looking contraptions made from PVC water pipe walking around the neighborhood with a box hung round their necks emitting strange sounds…

One of my Ham Radio interests is working DX on 160m – it's hard! Propagation is fickle, path losses are high and antennas are large but relatively inefficient. Living on the West Coast of the US also puts me at a disadvantage – a large number of DX entities are 6,000 miles away. Grabbing a new country on 160m especially if it's in Europe or the far Far East always results in a cheer or two.

My pursuit of 160m DX has been aided somewhat by the background noise level at my home being pretty low. I live in a small valley close to the hills that run down the Bay Area Peninsula – we're several miles from the nearest industrial facilities and that plus the terrain make for low background noise. Low on 160m is relative – in my case, a typical winter background noise level is S4-5.

Until three weeks ago.

I turned on the radio one Thursday night about 3 weeks ago to be greeted with an S9 noise level over large swaths of 160m – something in the area was generating a lot of RF interference – RFI. Here's the picture I saw on the display of the Flex 5000.

The RFI repeats every 18 KHz – it starts well below 160m (it appears down in the AM band but the strength of the AM stations covers it up) and goes up to almost 5 MHz. It's strong enough to make 160 and 80m unusable when its on.

This started my adventure as the RFI Hunter.

My first reaction was that likely this RFI was somewhere in my home, garage or the barn. So armed with a flashlight, I did what any good RFI Hunter would do first…

  • Grab the battery powered HF radio (an FT-817 in my case)
  • Hook it up to the 160m antenna (inverted L)
  • Kill the power at the main AC disconnect

The RFI continued unabated…

Ok – coming from somewhere else, how do I find it?

RFI can be from almost anything – switched mode power supplies, broadband modems, TV, stereo, computers, electric blankets, thermostats…

Sometimes you can get a good idea of the source by looking at the frequency, repetition rates, characteristics etc. of the RFI. If the RFI is very broad and drifts, the likely culprit is power line noise resulting from dirty or failing insulators on the power lines with arcing.

The signature of this RFI is perplexing…

The repeating pattern (every 18 KHz) suggested a switched mode power supply except that as you can see in the screen shot above, the frequency is very stable. The RFI doesn't drift. Clearly the next step was to attempt to locate the physical location of the RFI and see if that gave any clues…




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