Furuno FS-1570, Service Manual

Page: 143 / 322

5.4 TX/RX Board (05P0733)
5-26
Transmitting circuit
Fig.5.4.4 shows the block diagram of the transmitter on TX/RX board, 05P0733.
AF IN signal is converted to RF signal, and then, output to PA circuit from TX OUT
connector. The maximum output level is about +26 dBm (0.5 W)/50
Ω
.
R209, TX GAIN ADJ adjusts the output power from the transceiver unit. With
microphone input of -55 dBm and power data of 240, the output from the transceiver
unit is set to a quarter of the rated T/R output power. For example, the output power
from the transceiver unit is set to about 40 W on 150 W radiotelephone. The rated T/R
output power is adjusted by R76 (ALC) on TX FIL board. See chapter 7.
Fig.5.4.4 Block diagram of TX/RX board (05P0733)
In J3E mode, AF signal is frequency-converted to RF signal as shown in Table 5.4.3.
Table 5.4.3 Frequency converter and Transmitter IF frequency (J3E)
Frequency converter Local frequency IF signal
1st mixer U31 (NJM1496V) 456.5 kHz (3rd Lo) 455 kHz
2nd mixer U16 (NJM1496V) 72 MHz (2nd Lo) 72.455 MHz
3rd mixer U18 (NJM1496V) F0+72.455 kHz+1.5 MHz (3rd Lo) F0+1.5 kHz