26
UNDERSTANDING REPEATERS
Operation through a repeater, where you transmit on one fre-
quency and receive on another, is called
duplex
operation. Oper-
ation direct to another station, where you transmit and receive on
the same frequency, is called
simplex
operation.
A repeater is a station that receives a signal on one frequency
(the
input
frequency) and then retransmits that signal on a differ-
ent frequency (the
output
frequency). Repeater antennas are typ-
ically located at the tops of tall buildings or on antenna towers, so
a relatively low-power signal can reach the repeater. The repeat-
er retransmits the signal at a higher power. This gives your trans-
ceiver the ability to communicate over a much greater range.
To use a repeater, you must know the repeater’s input and output
frequencies. Repeaters are usually identified by their output fre-
quency. Thus, a repeater that has an output frequency of 442.200
is referred to as “the 442.2 repeater.” To determine the input fre-
quency, you must know the frequency
offset
(typically 5 MHz for
the 70 cm-meter band) and the
offset direction
(+ if you add 5
MHz to the output, or – if you subtract 5 MHz from the output).
Whether the offset is positive or negative depends on:
• which part of the band the repeater operates on
• local convention
• proximity of repeaters using the same two frequencies
To determine the offset and the direction, obtain a copy of
The
ARRL Repeater Handbook
(available from your local Ra-
dioShack store or directly from the ARRL) which lists the loca-
tions of repeaters as well as their frequency and offset
information.
A
+
above the displayed frequency indicates a positive offset,
while a
–
above the frequency indicates a negative offset. If nei-
ther
+
n
or
–
appears, the HTX-400 is set for simplex operation.
19-1104rc.fm Page 26 Friday, August 27, 1999 8:31 AM
