E F Johnson Company 2425331 Benutzerhandbuch

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The Busy Channel Lockout (also called Transmit 

Disable on Busy) feature automatically disables the 
transmitter if the channel is busy when the PTT switch 
is pressed. When the transmitter is disabled by this 
feature, “BUSY” is displayed, a busy tone sounds, and 
the transmitter is disabled.

The Busy Channel Lockout feature can be 

programmed to operate as follows. Each conventional 
channel can be programmed differently.

Off - Busy channel lockout is disabled and the trans-
mitter keys even if the channel is busy.

Noise - If a carrier is detected on the channel, the 
transmitter is disabled when the PTT switch is pressed.

Tone (NAC) - If an incorrect Call Guard (CTCSS/
DCS) or P25 NAC code (see Section 5.15.3) is 
detected, the transmitter is disabled when the PTT 
switch is pressed. An incorrect code is any code other 
than the one programmed for the current channel.

If Busy Channel 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.

5.5.1  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 radio to be 
functional. 

5.5.2  CALL GUARD SQUELCH ENABLE/

DISABLE

The SEL SQ option switch (if programmed) can 

be used to disable receive Call Guard squelch on 
analog channels or group ID code detect on P25 chan-
nels. When selective squelch is disabled, “SQ 
NORMAL” is flashed in the display, and when it is 
enabled, “SQ SELECT” is flashed. 

When “SQ NORMAL” is selected, the receiver 

unsquelches only if a carrier is detected, and scanning 
and P25 NAC detection are not disabled. The selected 
mode remains in effect until it is manually changed. 
Selecting another channel or cycling power does not 
reselect a default condition. 

5.5.3  TONE CALL GUARD SQUELCH

Tone-type Call Guard squelch utilizes subaudible 

CTCSS tones from 67-254.1 Hz. Although there are 42 
tones assigned, those above 33 (210.7 Hz) are normally 
not used because of their close proximity to the voice 
band which starts at 300 Hz. In addition, tones 11 (97.4 
Hz), 39 (69.3 Hz), 40 (206.5 Hz), 41 229.1 Hz), and 42 
(254.1 Hz) are normally not used because they may 
cause interference with adjacent tones.

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 
radio. Both the transmitting and receiving radio 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