Local Oscillator - Furuno FS-1570 Service Manual

5.4 TX/RX Board (05P0733)

5.4.2 Local oscillator

Fig.5.4.2 shows the block diagram of local oscillator on TX/RX board (05P0733).
Fig.5.4.2 Block diagram of local oscillator
Reference oscillator
The local oscillator on TX/RX board uses 18 MHz reference signal generated by REF
OSC board (05P0747). The reference signal is also used in PLL circuit on W/R board.
Y1 is an oven-controlled crystal oscillator. The oscillation frequency is adjusted to 18
MHz ± 5 Hz by the trimmer on Y1.
TEMP Signal
T-CPU board receives TEMP signal from REF OSC board to detect the oven
temperature. When the temperature lowers to the designed one, no transmission is made,
because the frequency deviates more than +10 Hz. The message, "OVEN COLD /TX
NOT READY: WAIT" appears.
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