E.F. Johnson Company 7780 Series Manuel d'utilisateur télécharger pdf (Page 26)

CONVENTIONAL FEATURES

5.4 BUSY CHANNEL LOCKOUT

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 5.16.3) 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 CALL GUARD SQUELCH

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 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 “SQ Normal” 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 “MON”

when the “SQ Normal” mode is selected (firmware

Version 1.28/2.6/3.6/4.2 or later).

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

1 2 ... 21 22 23 24 25 26 27 28 29 30 31 ... 72 73

Commentaires sur ces manuels

Pas de commentaire

E.F. Johnson Company 7780 Series Manuel d'utilisateur Page 26

Commentaires sur ces manuels

Produits connexes et manuels pour Les radios bidirectionnelles E.F. Johnson Company 7780 Series