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2. FUNCTIONAL DESCRIPTION
2.1 Transmission
Fig. 2.1 shows the signal flow in the transmitter.
The TX signal, TX0 and TX1, generated by CPU board (06P0258) is amplified by TRX board
(06P0241). The output of the power amplifier is impedance-matched with the transducer with a
matching transformer on PRA board (06P0259).
The +B voltage (VTX) from PWR board (06P0242) determines the transmitter output level
according to menu settings.
Table 2.1 Transmission level and control voltage
Signals Voltage Measuring Points
TX output 1019 Vpp Output of matching transformer on PRA board
TX output 713 Vpp Between TP6 and TP8 on TRX board
VTX (+B voltage) 77 V Resister "R13" on TRX board
Control Voltage TXV 3.0 V TP1 on CPU board
TX output level with
Dummy Load
592 Vpp Between TP6 and TP8 on TRX board with Dummy Load
2.2 Reception
Fig. 2.2 shows the signal flow in the receiver.
The echo received by the transducer is amplified by the Pre-Amplifier board and mixed with the
local carrier signal by the mixer U2 to generate 455 kHz IF signal.
The output of the buffer amplifier Q5 is sent to the rectifier, CR8/CR9, and then output to CPU
board from J3 #1.
The gain control signal (TVG), 0 to 5 VDC, is generated by CPU board according to control
panel setting. The TVG/AGC control circuit reshapes the TVG signal and output TVG signal,
0.5 to 1.7 VDC to amplifiers. When GAIN control is set to maximum, 1.7VDC is output.
Receiving the signal rectified by U7, the AGC feedback circuit also controls the TVG signal
level.
The output of TRX board is converted into digital data by A/D converter "U35" and applied to
Gate Array "U30" on CPU board.
The output of Gate Array is converted into R/G/B signal and sent to the display unit from #1, #2,
and #3 of J1.
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