TV Antenna Troubleshooting

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Interference

Appliance noise

Household motors and fluorescent lights often produce noise of the “120 sparks per second” variety. If you tune to an analog station (especially channels 2-10) you may see intense sparkles that are somewhat confined to a broad horizontal band. If so, you must find the appliance and fix it or replace it. Identifying the appliance is sometimes difficult. You might have to shut off the house breakers one at a time, watching to see when the sparkles go away. If every breaker but the TV is off and every appliance on that breaker but the TV is off and the sparkles remain then the noise source is either in a neighbour’s home or is a bad transformer on a utility company pole. (If you can walk around with a portable AM radio tuned to an unexplained buzzy hum, you might be able to further isolate the offending device.) If the source is in your neighbour’s home, brush up on your diplomatic skills. If it is the utility’s transformer, call them. They are obligated to fix it.

If the noisy appliance is in your house, you might need one or more of these fixes:

  1. Try fixing or replacing the device.
  2. Try replacing the device with a device containing some RF filtering.
  3. Try putting an RF noise filter on the power cord of the bad appliance.
  4. Try putting an RF noise filter on the power cord of your TV.
  5. If the TV and the appliance are on the same house breaker, move one to a different breaker.

Nulls in radiation pattern

Nulls in the radiation pattern can be useful. If you rotate the antenna so that a null points toward an interfering signal, that signal is eliminated. Some interference situations that might benefit from this trick include:

  1. Adjacent channel interference (a very strong station one channel up or down)
  2. Co-channel interference (two weak stations on the same channel)
  3. Multi-path interference (usually caused by the direct path being blocked)
  4. A very close transmitter (a neighbourhood FM station, police station, taxi company, etc.)
  5. An industrial noise source (a factory, a clinic, a malfunctioning power transformer)

For example, the Channel Master 4228 has nulls on both sides at 30 and 90 degrees:

Channel master diagram

(Please note the antenna listed in this diagram relates to U.S. products, but is still relative.)

Yagi/Corner-reflector antennas have no nulls. LPDA antennas have nulls at 90 degrees, but LPVA antennas have no nulls. To make rabbit ears have nulls (at 90 degrees) lower them into a straight dipole.

In a multi-path situation, a null will work if there is only one strong ghost. (Find an analog channel close in frequency and from the same direction. Examine it for ghosts.) If there are multiple very strong ghosts then a better approach is a very high-gain (very directional) antenna with little reception to the side or rear.

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