Interference from Radio Transmitters

Dec 10,2006 00:00 by admin
Interference usually occurs when radio transmitters and electronic equipment are
operated within close range of each other.The following causes interference:
Incorrectly installed radio transmitting equipment
An intense radio signal from a nearby transmitter
Unwanted signals generated by the transmitting equipment and not
enough shielding or filtering in the electronic equipment to prevent it
from picking up those unwanted signals
Any signal other than the desired signal is called an unwanted signal, or spurious
radiation. Spurious radiation includes harmonic radiation, usually in the form
of standing or traveling waves. Use a spectrum analyzer, a calibrated field intensity
meter, or a frequency-selective voltmeter to measure unwanted radiation.A
spectrum analyzer is a device that measures the frequency components of a radio signal. It provides a visual image of how the amplitude of a radio signal varies in
relation to its frequency. If adjusting the channel does not solve the problem
completely, you should permanently install a low-pass band filter in the transmitter
antenna feed line after all the other accessories.
Standing waves are a form of spurious radiation causing undesired effects that
occur when two or more waves of the same frequency are present at the same
time and do not travel away from their source.This may happen, for example,
when the transmitter, transmission line (antenna cabling), or antenna are not
properly matched to each other. Incorrectly terminated or damaged antenna
cabling is a typical source of standing waves. When this happens, the transmitted
signal to the antenna is reduced because the damaged cable is transmitting
unwanted signals.