TD 90227GB
2006-09-18/ Ver. C
System Installation
On Site Paging System
2
• The bus network must be open, never a loop.
• Use only twisted-pair wiring for extension of the system bus.
• Maximum length is 3 km for data buses and 500 metres for the speech bus. Distances
exceeding this require modems.
1.3
Data Buses
The A-bus is used for data communication between the modules and the D-bus for
communication between Central Unit and Terminal transmitters. Both the A- and D-buses
carry constant communication. This can be seen on an oscilloscope as a pulse train. The
normal level is 8-10 Vp-p measured from A1 to A2, and D1 to D2. If several units are
connected to the buses or if the lines are long, the level will be lower but must be at least
0.6 Vp-p. The data buses are polarized.
The four data buses (A, B, C, and D) use balanced lines and operate according to EIA
standard RS-485 and CCITT recommendations V.11 and X.27.
• A- and B-buses are identical and are used for connection of interface modules.
• C-bus is used for communication between different installations, i.e. between two or
more Central Units.
• D-bus transmits pagings in transmit format from the Central Unit to one or several
Terminal Transmitters.
1.4
Speech Bus
The SP-bus is a two-way line connecting all modules that handle the speech signal. The
SP-bus is transformer coupled. The signal level during speech is about 2 Vp-p measured
between SP1 and SP2.
1.5
FL-bus
The FL-bus is a one-way speech bus to terminal transmitters. The FL-bus is used in
frequency locked systems. In contrast to the speech bus, the FL-bus is driven by a low
impedance driver. The FL-bus is polarized.
1.6
Wire Type
Only twisted-pair cables are to be used. Suitable types are, for example EKKX 4 x 2 x 0.5 or
EKKX 10 x 2 x 0.5.
1.7
Wiring Lengths
Max total wiring lengths are:
A-bus
3000 m
Data communication between modules
B-bus
3000 m
Data communication between modules
C-bus
3000 m
Data communication between systems
D-bus
3000 m
Data communication from central to terminal transmitters
FL-bus
3000 m
1-way SP-bus to terminal transmitters
R-line
1000 m
Speech and data between fixed receiver and receiver interface
SP-bus
500 m
2-way speech bus