The most common two-way radio systems operate in the VHF and UHF parts
of the radio spectrum. Because this part of the spectrum is heavily used for
broadcasting and multiple competing uses, spectrum management has become an
important activity of governments to regulate radio users in the interests of
both efficient and non-interfering use of radio. Both bands are widely applied
for different users.
UHF has a shorter wavelength which makes it easier for the signal to
find its way through smaller wall openings to the inside of a building. The
longer wavelength of VHF means it can transmit further under normal conditions.
For most applications, lower radio frequencies are better for longer range and
through vegetation. A broadcasting TV station illustrates this. A typical VHF
TV station operates at about 100,000 watts and has a coverage radius range of
about 60 miles. A UHF TV station with a 60-mile coverage radius requires
transmitting at 3,000,000 watts. Another factor with higher frequencies (UHF)
is that smaller sized objects will absorb or reflect the energy more which
causes range loss and/or multipath reflections which can weaken a signal by
causing an "Out of Time/Out of Phase" signal to reach the antenna of
the receiver (this is what caused the "Ghost" image on old over the
air television).
If an application requires working mostly outdoors, a VHF radio is
probably the best choice, especially if a base station radio indoors is used
and an external antenna is added. The higher the antenna is placed, the further
the radio can transmit and receive.
If the radios are used mainly inside buildings, then UHF is likely the
best solution since its shorter wavelength travels through small openings in
the building better. There are also repeaters that can be installed that can
relay any frequencies signal (VHF or UHF) to increase the communication
distance.
There are more available channels with UHF. Since the range of UHF is
also not as far as VHF under most conditions, there is less chance of distant
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