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Measuring point: P4 #1 - P4 #4
Frequency:75 kHz
Fig. 2.2 TX waveform
Receiver Circuit
The received signal from the transducer is first amplified by the RF amplifier and then
mixed with the local oscillator output to get a 455 kHz IF signal. The IF signal (Fig.2.4 CH1)
is amplified and fed to the next stage's full wave detector. The output of the detector (Fig.
2.4 CH2) is A/D converted to eight bit echo data at specific sampling intervals.
The AMP PWR CONT circuit supplies + 5 V (AMP5V), which is controlled by APWR signal
from the CPU, to the TVG amplifier only during the reception period to conserve battery
consumption.
CH1
CH2
Measuring point: CH1 -- TP3
Fig.2.4 Waveforms of received echo signal
TVG Circuit
Triggered by the TVG (Time Varied Gain) signal from the CPU on the CONT A board, the
TVG circuit generates an exponentially rising TVG voltage (TVG curve). This voltage
controls the gain of the amplifier in such a way that the gain is minimum at the time of
transmission and gradually increases with time. The TVG curve is factory set to a 30 log
curve suitable for fish detection.
Fig.2.6 shows the waveforms of the TVG voltage.
100V/DIV
0.2ms/DIV
CH1
200mV/Div
1ms/Div
CH2
2V/Div
1ms/Div
CH2 ---TP2(ESIG)
2-3
Measuring point: TP6 on TRS.A board
Frequency:75 kHz
Fig.2.3 TX trigger: TSMT
Measuring point: TP7 (carrier)
Fig.2.5 Waveform of carrier signal
2V/DIV
0.5ms/DIV
CH1
200mV/Div
1us/Div
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