Draft 02 - Sep 1 2015
5-4
Viking Mobile Radio Operating Manual
Conventional Mode Features
5.4.1
Call Guard Squelch Enable / Disable
The Normal/Selective option switch (if programmed) can be used to disable receive Call
Guard squelch (Normal/Selective Squelch) on analog channels or group ID code detection
on P25 channels. This option is also selectable via the menu. When selective squelch is
disabled, “SQ NORMAL” is flashed in the display. When it is enabled, “SQ SELECT” is
flashed on the Standard Control Head and “Squelch Selective” on the Lightning Control
Head.
When Normal Squelch is selected, the receiver unsquelches only if a carrier is detected.
Scanning and P25 NAC detection are not disabled with this mode selected. The selected
mode remains in effect until it is manually changed. Selecting another channel or cycling
power does not reselect a default condition. There is a programmable option to display the
monitor icon when the Normal Squelch mode is selected.
5.4.2
Tone Call Guard Squelch
Tone-type Call Guard squelch uses 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 eliminates 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
used. The radio can be programmed to turn OFF the reverse burst feature so that the
squelch tail is not eliminated.
5.4.3
Digital Call Guard Squelch
Digitally Coded Squelch (DCS) uses digital data instead of subaudible tones to control the
squelch. This data consists of continuous repetitions of 23-bit words. There are 84 DCS
digital data tones to select from. 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.
