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Adventures with Radio Frequency Interference

People who enjoy listening to the High Frequency radio spectrum (3-30 Mhz) face an ever increasing problem of Radio Frequency Interference. Think of RFI as noise pollution to the radio spectrum. This video describes some RFI problems and details a series of diagnostic steps that can help identify noise sources.

Many newcomers to ham radio and shortwave listening quickly become discouraged by the amount of radio frequency interference in their homes and neighborhoods. This is especially true when using indoor antennas. The main culprits are those little power supply cubes that we use for most consumer electronics devices. They are called switched mode power supplies (SMPS) and they are everywhere. SMPS are actually designed to emit radio spectrum pollution as part of their effort to use electricity more efficiently. While various regulatory bodies provide standards requiring manufacturers to ensure that these emissions are at a very low level, these standards are not enforced in any meaningful way.

In particular, this video provides information on using a number of important diagnostic tools including:

  • Building a cheap and easy direction finding loop to figure out exactly where the noise is coming from.
  • Using software defined radio to analyze the HF frequency spectrum at your location.
  • Using an audio spectrum analyzer to understand the noise signature, particularly for power line and power supply related noise.
  • Hooking up a remote connection to your listening post so that you can demonstrate the RFI effect at different locations. For example, if you are receiving interference from a plasma television, you can actually demonstrate what happens when your neighbor turns his television on and off.
  • Fighting and reducing interference using noise cancelling tools.

A good introductory source of information about RFI is provided by the ARRL.

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