Radio Frequency Interference

There can be a few reasons as to why Communications equipment cause interference to other communications or digital equipment as well as to why radio communications equipment receive interference.

Symptom: For instance, the most common type of interference being caused to Televisions by Communications equipment. Different types of lines on the TV also indicate different types of interference. One main reason of interference is the distance between the your transmitting aerial system and the television reception aerial.

Cure: One cure can be to place a 'high-pass' filter in series with the television co-axial cable going into the television. I wont go into detail but the arrangement of Capacitors and inductors in the filter pass higher frequencies while attenuating lower frequency signals.

Symptom: Audio equipment interference, such as HI-FI systems.

Cure: Capacitors used to pass only audio frequencies but not allowing higher frequencies to pass wired into the audio system.

Cars are also a breeding ground for interference, but not generated by the CB or radio equipment onboard but received by it instead. The car ignition system generates noise co-inciding with the engine rpm because of the high voltages switching to fire the spark plugs in the engine. Alternator whine is another typical and annoying interference into the CB equipment. Again capacitors can be used to suppress alternator whine.

If you have problems with engine noise in a mobile installation, there are several things you can do to reduce or eliminate the problem.

Of course, the best performance can be obtained from a more expensive radio with better noise suppression circuits. These measures, however, will improve the engine noise levels for nearly any mobile radio.

Engine management systems can also cause interference because of their high switching rates in digital logic. However, engine management systems are also very susceptible to interference from radio transmitters but rarely fail to operate properly as a result. Avionics (Aviation electronics such as auto-pilot, and landing systems) do however suffer seriously from interference from digital equipment. Avionic systems are very sensitive.

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This Web page was last updated on Friday September 21, 2001

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