Specifications

Simplex Channel
A simplex channel radio system
transmits and receives on one frequency.
Simplex is used for local
communications - for example, "Person
to Person" communications when in sight
of one another. Since VHF radio signals
are generally limited to line of sight,
range is short. It is possible for a user to
be able to hear one side of a
conversation, but not the other because
one station is in range of you, and the
other is not.
Duplex Channel
VHF repeaters are said to work on a duplex channel. A transmission is received on
an “input” frequency and simultaneously retransmitted on an “output” frequency
(hence the name Duplex). Repeaters are usually placed on a mountains summit
(where available/accessible), on top of high buildings or on large towers to increase
the range and accessibility by handheld VHF units. Solar cells and batteries normally
back-up the power supplies of
these systems.
It is important to remember when
using a “repeater channel” to key
the radio approximately one
second before beginning to speak
as most repeater systems have a
power save mode to conserve the
batteries. Hence the saying
“think, press and talk”, or
“engage brain before mouth” (This has nothing to do with the “key-up delay).
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