Transmission Circuit; Tx Board (05P0856): Common Board - Furuno FS-1575 Service Manual

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7.2 Transmission Circuit

The TX board is common to the three models.

36-kHz voice, DSC, and NBDP TX IF signals modulated with the DSP of the T-CPU

board are inputted to the TX board and converted up to RF frequency.

The RF frequency is converted to an IF frequency of 71.964 MHz by the IF signal at a

frequency of 72 MHz in the Mixer circuit. The IF frequency of 71.964 MHz is

converted to a transmission frequency at Lo frequency in the 2nd Mixer circuit.

Furthermore, this TX board controls TX output power. The TX board outputs power to

the PA board in case of the FS-1575 system and to the DRV board in case of FS-2575

and FS-5075 systems.

The maximum TX output power of the TX board is +12dBm into 50-ohm load.

Major built-in circuits of the T-CPU board are TX IF amplifier circuit, power control

circuit, frequency conversion circuit, 36-MHz VCTCXO (Voltage Controlled

Temperature Crystal Oscillator; reference oscillator), PLL synthesizer circuit, and TX

board self-test circuit.

7. UNLOCK TX

8. ST DDS TX

9. ST PLL TX

10. ST SR TX

22. OVEN 12V (N.C)

27. TX HW VER0

29. TX HW VER1

CONFIDENTIAL (internal use only)

This confidential document is used only by FURUNO authorized persons.

It is strictly prohibited to reproduce the document in whole or in part without prior written permission of FURUNO.

Fig. 7.2.1 TX Board Block Diagram

USB: f + 71.964MHz + 1.5kHz

LSB: f + 71.964MHz - 1.5kHz

TLX: f + 71.964MHz

7.2 Transmission Circuit

Fs-2575 Fs-5075