E.F. Johnson 5100 SERIES Service Manual - page 22
OPERATION
2-11
September 2001
Part No. 001-5100-001
transmitter even if the channel is not in use. In this
case, the channel must be monitored manually as
follows:
Rx Indicator - With scanning disabled, note if the indi-
cator on the top panel is steady green. If it is not, the
channel is not being used and you can transmit your
call. If it is green, the channel may be busy and you
should not place your call (see next paragraph).
Monitor Mode - There may be times when the busy
indication is displayed even though no one is using the
channel. Monitoring should then be performed by
disabling Call Guard squelch using the Normal/Selec-
tive option switch as described in Section 2.6.6 or the
monitor mode described next.
2.6.4 MONITOR MODE
The monitor mode temporarily disables squelch
control features (such as Call Guard
®
squelch) so that
all messages are heard on the selected channel. It also
overrides the Busy Channel Lockout feature (see next
section) and temporarily halts scanning.
To monitor the selected channel, select the
monitor mode by briefly pressing or pressing and
holding the Monitor option switch (if available). The
receiver unsquelches and a rushing noise or voice is
heard when the monitor mode is enabled. To disable
the monitor mode and return to normal operation,
release the Monitor switch or press it a second time.
If scanning is enabled, pressing and holding the
Monitor option switch monitors the current scanned
channel instead of the selected channel if applicable.
2.6.5 BUSY CHANNEL LOCKOUT
The Busy Channel Lockout feature (also called
Transmit Disable On Busy) automatically disables the
transmitter if the channel is busy when the PTT switch
is pressed. When a busy condition is detected by this
feature, the transmitter is disabled, “BUSY” is indi-
cated in the display, and a tone similar to a standard
telephone busy tone sounds until the PTT switch is
released. The transceiver can be programmed to
operate in one of the following modes on each
channel:
Off -
Busy channel lockout is disabled and the trans-
mitter keys even if the channel is busy.
Noise -
The transmitter is disabled if a carrier is
detected on the channel.
Tone -
The transmitter is disabled if an incorrect Call
Guard (CTCSS/DCS) or NAC code is detected (see
Section 2.6.6). An incorrect code is any code other
than the one programmed for the current channel.
If busy override is permitted by programming, it
is possible to transmit even when the transmitter is
disabled by this feature. Simply release the PTT switch
and then quickly press it again.
2.6.6 CALL GUARD SQUELCH
Introduction
Tone or digital Call Guard squelch (also called
CTCSS/DCS signaling) can be programmed on each
conventional analog transmit and receive channel in
any order desired. The reverse burst and turn-off code
are always transmitted and also detected on channels
programmed with Call Guard squelch.
The Call Guard squelch feature eliminates
distracting messages intended for others using the
channel. This is done by using a subaudible tone or
digital code to control the squelch. This tone or code is
unique to a user or a group on that channel. This tone
or code is transmitted with the voice signal but is not
heard because it is in the subaudible range and is atten-
uated by a filter. Call Guard squelch must be used in
both the transmitting and receiving transceiver to be
functional.
Call Guard Squelch Enable/Disable
To disable Call Guard (Selective) squelch so that
all messages on the selected or scanned channels are
heard, press the Normal/Selective option switch (if
available) so that “NORMAL is flashed in the display.
Then to re-enable Call Guard squelch, press the
Normal/Selective switch again so that “SELECTIV” is
flashed. The mode selected by this switch does not
change when other channels are selected or power is
cycled. Call Guard squelch can also be disabled by the
monitor mode described in Section 2.6.4.