|
Part 2: Technical Tidbits
The 2-way radio systems heard on scanners are similar in many ways to
radio signals heard on commercial FM radio and television. All radio
signals are examples of electromagnetic waves, like light waves, infrared,
and X-rays. The diagram below shows relationship between radio frequencies
and other electromagnetic waves. The 2-way radio systems you will hear on
a scanner radio are in the "VHF" and "UHF" part of the spectrum.  .
In both 2-way radio systems and commercial FM radio, stations are
separated by broadcasting on different frequencies. For example, a popular
FM music station may be on 103.7 MHz. Another music station may be on
105.3 MHz. Your radio will tune to one station while filtering out the
other station because the two stations are on different frequencies. A
busy police dispatch station may be on 154.720 MHz while another may be
found on 155.700 MHz. Groups of adjacent frequencies are referred to as
radio bands. The FM Broadcast Radio Band is between 88 to 108 MHz while
2-way radio systems are most commonly found in the following radio bands:
30-50 MHz, 150 to 162 MHz, 450 to 470 MHz, and 851 to 869 MHz. The Radio
Spectrum Diagram below shows most of the major radio bands that scanners
receive. This website will help you select a model that includes the radio
bands and features you need. 
The range of 2-way radio communications depends primarily on the height
of the antenna and the power used. Hand-held radios using only a few watts
can only be heard by scanners from a few miles away while base stations
and repeaters usually can be heard from 30-40 miles or more. Aircraft in
flight can often be heard over 150 miles away, making them an easy catch
for your radio scanner!
|
