The AM Band

Despite 45 years of rumours of its imminent demise, AM Radio is still a powerful force in North America.  Even the CBC has been forced to abandon its plans to move all of its stations to FM due to AM’s superior coverage.  For example, in Vancouver, CBU-690 still exists thanks to the CRTC’s denial of a CBC application to replace it with a number of FM transmitters that would still leave a sizable number of its listeners without a usable signal.

At the beginning of the 1970s, rumours circulated through the world of DX’ers that the FCC was just about to close down the AM band and force all stations to move to FM.  Up to that point in time, it was very unlikely that any FM station in North America was making money.

Although fewer AM stations seem fully prepared for emergencies, AM coverage is superior to FM as a Disaster communications vehicle.

Reducing RFI

Reducing Radio Frequency Interference (RFI) that effects AM reception is really a four step process:

  1. Locate the source;
  2. Determine the cause;
  3. Fix or replace the culprit;
  4. Measure the improvement.

RFI test equipment exists, but a receiver like the CC Skywave has the necessary features to get the job done:

  1. AM reception;
  2. Portability;
  3. An S Meter or equivalent;
  4. Directional antenna;
  5. 137 MHz coverage

Tuning to a quiet AM frequency is only one method of isolating RFI from signals of real radio stations. RFI test equipment usually monitors 137 MHz, a usually quiet frequency from a broadcast perspective, where RFI tends to propagate much shorter distances than the standard AM band. Which makes it easier to locate local RFI as signal strength increases quickly as you get closer to the source.

Measuring the strength of the RFI helps locate it and measure any improvements, but listening to a receiver’s audio level (Volume) does not indicate how strong the signal is. Receivers are built to deliver the same audio level no matter how strong or weak the station’s signal is. Displaying the signal strength on at least a scale of four will provide the basics of an S Meter.

The strongest sources of RFI on the AM band that I currently experience are:

  • Air conditioning – whole house
  • Desktop Computer – same room
  • Digital Audio Recorders – nearby
  • Lightning – many miles away