Codan 8525B Series Technical & Service Manual

4-30 Technical Description 8525B/8528 Technical Service Manual
Issue 6 Publication No: 15-02036
4.11 Selective Calling (04-02250)
Selective calling facilities may be either internal to the 8525B or 8528, or by
external control using option PS. It should be noted that option PS cannot
be used when internal selective call is fitted.
The following selective call variants are available:
• SE2 4–digit encoder internally preset.
• SDE 4–digit encoder/decoder—separate internal presets for encode and
decode.
• SDEM 4–digit encoder/decoder—internally preset for decode,
externally set for encode.
Note: When an 8530 control head is used with SDEM, the encode
switches only are mounted on the control head while the remainder
of the circuit is in the transceiver. SE2 uses assembly 08-03303;
SDE and SDEM use assembly 08-03300.
Selective Calls are sent as FSK signals using 1700Hz and 1870Hz at 100
Baud.
4.11.1 Selective Calling
The call is initiated by pressing the Call pad on the front panel. On
recognising the request for a call, the microcontroller first checks that the
channel selected is one on which selective calls are programmed. If it is, the
microcontroller generates the required codes including the Called Address
and Self Ident codes set in the transceiver. The settings of each pair of
switches are encoded by the corresponding 8-bit I/O port IC4, IC5, IC6 and
IC7 and sent to the microcontroller as serial data when the appropriate port
is addressed. The Self Ident switches on the PCB are used for all options.
When external digiswitches are fitted (SDEM), the microcontroller
disregards the settings of any internal Called Address switches duplicated on
the panel or control head.
The microcontroller (04-02451) applies the generated code to the tone
generator IC12. The resulting FSK tones from IC12 pin 10 are filtered by
C20 and R21 and applied via J3 pin 9 to the auxiliary compressor input of
the Audio and IF 1650kHz PCB. The FSK tones are also attenuated by R23
and applied as a side tone via J3 pin 10 to the auxiliary LS input of the
Audio and IF 1650kHz PCB. At the same time, the microcontroller
generates a PTT signal so that the FSK tones are transmitted. On completion
of the coded transmission, the PTT signal is removed and the transceiver
returns to the receive mode.
Note: If selective and 2-tone calling are required on the same frequency,
the frequency must be allocated to two channels; one with selective
calling and one with 2-tone calling.

Codan 8525B Series Specifications

General

Brand	Codan
Model	8525B Series
Category	Transceiver
Language	English