CONVENTIONAL MODE FEATURES
26
A reverse burst is transmitted when the push-to-
talk switch is released and also detected when calls are
received. It is a 180-degree phase reversal for a period
of time determined by the tone frequency, and it elimi-
nates the squelch tail (noise burst) in the receiving
transceiver. Both the transmitting and receiving trans-
ceiver must be equipped with this feature for it to be
utilized.
5.5.4 DIGITAL CALL GUARD SQUELCH
Digital Call Guard squelch (DCS) uses digital
data instead of subaudible tones to control the squelch.
This data consists of continuous repetitions of 23-bit
words. No bit or word synchronization information is
used. When the push-to-talk switch is released, a turn-
off code is transmitted which eliminates the squelch
tail similar to the reverse burst.
Although there are thousands of possible code
combinations with 23 bits, only 83 are unique with the
data scheme used. The number specified when the
code is programmed is actually a seed for a special
algorithm used to generate the 23-bit data word. The
data is transmitted at a rate of 134.4 bits per second.
Therefore, approximately six words are transmitted
each second. When the data is decoded, 23-bit samples
are taken and then the bits are rotated to determine if a
valid code was received.
5.5.5 SELECTIVE SQUELCH CODE SELECT
(CTCSS/DCS/NAC)
NOTE: Call Guard codes can be permanently repro-
grammed by keypad programming (see Section 5.17).
A different CTCSS/DCS/NAC squelch code can
be temporarily selected if the Selective Squelch option
switch or menu parameter and a CTCSS/NAC code
list have been programmed. This feature allows the
normal transmit and receive Call Guard programming
to be temporarily overridden with a code selected from
this list.
The CTCSS/DCS/NAC list is programmed with
up to sixteen tone (CTCSS) or digital (DCS) Call
Guard codes. In addition, for operation on Project 25
channels, each position can be programmed with an
NAC code.
When the Call Guard code is changed using this
feature, it remains selected even if other channels are
selected. However, if transceiver power is cycled or a
talk-around channel is selected, the normal codes are
reselected. When scanning, the selected code also
applies to all scanned channels. If both analog and
digital (Project 25) channels can be selected or
scanned, the CTCSS/DCS code for the selected posi-
tion is used for analog channels and the NAC code for
the selected position is used for P25 channels. If a
channel is programmed for mixed mode operation, the
selective squelch type (analog or digital) programmed
for the transmit mode determines the selective squelch
type used.
Proceed as follows to select a preprogrammed
Call Guard code:
1. Press the Selective Squelch option switch or select
the Sqlch Code menu mode parameter. Then press
the Up/Down switch to select the desired code. The
display indicates “SEL SQ xx” where, “xx” is the
selected code from 1-16.
2. To select the displayed code and return to the normal
display, press the F2 (Select) key or the Selective
Squelch switch again.
3. To check which code is selected, press the Selective
Squelch switch once to display the current selection
and then again to return to normal operation.
4. To return to the normal selective squelch codes,
select “DEFAULT” in this mode. As previously
described, the normal codes are also automatically
reselected whenever transceiver power is cycled or
a talk-around channel is selected.
5.6 PENALTY TIMER
A penalty timer may be programmed on conven-
tional systems to prevent transmissions for the
programmed time after the time-out timer disables the
transmitter (see Section 4.3). The penalty timer can be
programmed for the same times as the time-out timer,
and timing starts when the PTT switch is released. If
the PTT switch is pressed during the penalty time, the
time-out indication occurs again and the transmitter
remains disabled. When the penalty timer expires, a
beep sounds and the transmitter can be keyed.
Summary of Contents for 5100 SERIES
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