EF JOHNSON 5100 ES II, Operating Manual

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5-4 5100 ES Model II/III Portable Radio Operating Manual December 2006
Conventional Mode Features
5.4.1 Call Guard Squelch Enable/Disable
The Normal/Selective option switch or menu parameter (if programmed) can be used to
disable receive Call Guard squelch on analog channels or group ID code detection on P25
channels. When selective squelch is disabled, “Sq Normal” is flashed in the display, and
when it is enabled, “Sq Select” is flashed.
When “Normal” is selected, the receiver unsquelches only if a carrier is detected.
Scanning and Project 25 NAC detection are not disabled with this mode selected. The
selected mode is in effect until it is manually changed again. 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” mode is selected.
5.4.2 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 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
utilized.
If the user would like to hear the squelch tail, then the reverse burst transmission can be
disabled by checking the “Disable Squelch Tail Elimination” checkbox.
5.4.3 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.