Service manual

OPERATION
3-30
April 2001
Part No. 001-9800-203
squelch control output from the decoder is the IN2/IN3
wire-outs of the option slots on the audio/logic board.
Outputs which may control a decoder or encoder are
the OUTPUT A and B wire-outs. These are CMOS
outputs with a 470-ohm series resistance and a typical
maximum source and sink current of 2 mA.
To program the transceiver for external encoder
or decoder operation, the I/O lines just described must
be programmed for the desired function and active
state as described in Section 4.9. In addition, the appli-
cable conventional group must be programmed for
AND EXT = Yes as described in the following infor-
mation.
Decoder (Receive Mode) Operation
If an external decoder is to be used, program the
applicable conventional group for AND EXT = “Yes”.
(RX CCG category). The Call Guard and external
decoder functions are “ANDed” which means that
both Call Guard squelch (if programmed) “and” an
external decoder must detect the proper code for the
receiver to unsquelch. If “None” is entered for the Call
Guard type then only the proper external decoder code
is required.
The input control line that is used (IN2 or IN3)
then must be programmed for the “Ext Call Guard Sq”
function (see preceding paragraph). If the active state
of this line is programmed “high”, a high output from
the decoder unsquelches the receiver (unmutes the
audio). Conversely, if the active state is low, a low
signal unsquelches the receiver.
Once the receiver unsquelches, it remains in that
condition until the control line from the decoder
changes states or a carrier is no longer detected. To use
the microphone hanger as a decoder reset line, an
output line such as Output A or B can be programmed
for the “Monitor Hanger” function. If the active condi-
tion is “high”, this line is high when the microphone is
on-hook and low when it is off-hook. Operation of this
line is not affected when off-hook detection is
disabled, and the Monitor option switch does not
control this function.
Encoder (Transmit Mode) Operation
If an external encoder or encoder/decoder is used
to transmit a special sequence when the PTT switch is
pressed, program the applicable conventional group
for AND EXT = “Yes” (TX CCG category). As in the
receive mode, the Call Guard and external decoder
functions are “ANDed”. Therefore, if transmit Call
Guard squelch is programmed, it is also transmitted.
The output control line that is used (Output A or
B) then must be programmed for the “Send Call Guard
Sq” function and the desired active state. Then when
the transmitter is keyed, this line goes to the active
state and shortly after, the Transmit line goes high.
These lines then go back to the inactive state when the
transmitter is unkeyed.
Scanning With An External Decoder
Groups programmed for both Call Guard squelch
and an external decoder are scanned for the normal
period (see Section 3.7.7). If only an external decoder
is programmed on a group, it is scanned for a fixed
period of 200 ms to determine if the correct code is
detected. If an external decoder is programmed on a
priority group, the external decoder is not detected.
3.10 SUPERVISORY TONES AND DISPLAY
MESSAGES
3.10.1 GENERAL TONES
NOTE: The display messages and menu parameters
mentioned in the following information are not avail-
able with low tier models.
The following tones are heard at various times
when operating this transceiver. Some or all of these
tones can be disabled by the user if the menu
“TONES” parameter is available (see Section 3.6.26).
If the menu parameter is not available, these tones can
be selected only by the PC programmer.
Busy Tone - This tone is similar to the standard tele-
phone busy tone, and it indicates that the LTR radio
system is currently busy. It is produced by turning
combined 480 and 620 Hz tones on and off at a 4 Hz
rate. This tone sounds with all types of LTR calls
(even if the proceed tone is enabled), and “BUSY” is
indicated on the lower line of the display when it
sounds. It does not sound on conventional systems.