Skanti TRP 9250, Technical Manual, Page: 144 / 289

Programmable Communication Processor 717 (optional):
This board constitutes a combined DSC/Telex modem with two demodulators and one modulator.
It contains a 16-bit microprocessor with its peripherals, a real time clock, interface circuits for alarm,
handset hook, and key input signals, interface circuits for alarm and key output signals, four
asyncronous communication interface adaptors for serial communication with the TU Control board,
navigational equipment (NMEA), printer/remote control, and PC. The driver/receivers for PC and
NMEA are opto-isolated with driver power delivered from the equipment connected. The modem
communicates with the control unit via the ScanBus using a dedicated CAN controller chip. The
modulator generates an FSK signal at 1.7 kHz which is routed to the exciter. The input signals for
the two demodulators are coming from the dedicated DSC watch receiver and the RX/EX Signal
Path 715 respectively.
Single Channel Receiver Board 914 (optional):
The single channel receiver is fixed tuned to the DSC distress frequency 2187.5 kHz. It includes
antenna input protection, pre-selection filter, 1. mixer where the input signal is mixed with a 1.7325
MHz signal originating from an oven controlled oscillator, a narrow-band 455 kHz crystal filter, IF
amplifier, and 2. mixer. The local oscillator signal for the 2. mixer is generated by a 7.2528 MHz
crystal oscillator the output of which is divided by 16 to produce a frequency of 453.3 kHz. The
output from the mixer is low-pass filtered and the AF signal centred around 1.7 kHz is finally amplified
in AF amplifier.
Synthesizer Board 912 (optional):
The Synthesizer Board 912 is similar to PCB 911 but without master oscillator and gets the reference
signal from PCB 911. The Synthesizer Board 912 is used together with the optional PCB 915 to
constitute a built-in DSC Scanning Receiver.
Receiver Signal Path 915 (optional):
The receiver signal path includes antenna input protection, pre-selection filters, 1. mixer where the
input signal is mixed with the 1. local oscillator signal of the synthesizer, a 45 MHz crystal filter, 1.
IF amplifier, and 2. mixer. The local oscillator frequency for the 2. mixer is 44.544 MHz corresponding
to a 2. IF frequency of 455 kHz. The 2. IF filter is a narrow-band crystal filter. In the 3. mixer the IF
signal is mixed with 456.7 kHz producing an AF signal centred around 1.7 kHz.
TRANSCEIVER UNIT TU 9250 TECHNICAL DESCRIPTION
TRP 9250 TECHNICAL MANUAL 4-7