Pll Synthesizer Circuit; Wr Board Self-Test Detection Circuit; Power Supply For Pre-Amplifier - Furuno FS-1575 Service Manual

4. PLL Synthesizer circuit

A circuit that outputs 1st Lo frequency consists of PLL and DDS circuits.
A 36 MHz reference frequency from the TX board is inputted to "U12" PLL IC. The PLL IC
converts the 36 MHz reference frequency to a 6 MHz reference frequency to output a 396
MHz frequency.
A 396 MHz frequency outputted from the PLL circuit is inputted in the DDS circuit (U11),
and the 1st Lo frequency is outputted from the DDS circuit according to data on received
frequencies up to 10 Hz digits.
The 1st Lo frequency is injected in the 1st mixer to convert a received signal (WR1: F+35.964
MHz, WR2: F+44.964 MHz) to the 1st IF signal.
The 2nd Lo frequency generates a 45 MHz frequency based on the 36 MHz reference
frequency from the TX board by adding 36 MHz for the WR1 board and by adding 36 MHz
and 9 MHz with U10 and T6 for the WR2 board.
The 2nd Lo frequency is injected in the 2nd mixer to convert a received signal to the 2nd IF
signal of 36 kHz.

5. WR board self-test detection circuit

Check signals outputted to the T-CPU board are the UN-LOCK, WR HW VER, and WR
INST signals.
1) UN-LOCK
PLL circuit "lock or unlock" detection signal. When it detects that the PLL circuit is
unlocked, reception will be stopped and an error message saying "WARNING: WR1 (2)
PLL UNLOCK!" will be outputted.
2) WR HW VER
WR board hardware information. This information will be displayed when selecting
[MENU] -> 9.SERVICE -> 5.TEST -> 1.VERSION.
3) WR INST
Used to determine whether or not the WR board is mounted.
For example, if no WR2 board is mounted, the RX board will watch scan upon
receiving DSC general frequency.

6. Power supply for pre-amplifier

To connect FAX-5 (pre-amplifier) to the WR antenna, 12V power has to be supplied for the
preamplifier.
When a FAX-5 + 2.6m whip antenna is connected to the WR1 and WR2 boards, respectively,
set "J3" of the WR boards to the "active" side, and then supply 12V power to the FAX-5
pre-amplifier.
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.
7-53
7.4 WR Board