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The echo data from the CPU consists of 8 bits (4 bits for echo data and 4 bits for frequency
calibration data). The CPU determines the calibration value from timer's output count and
writes it on the designated frequency calibration data bits to obtain 50kHz (33kHz, 40kHz)
in no-modulation (no signal) state and 51kHz (34kHz, 41kHz) in maximum modulation
state at TP1 and TP2.
Echo Data
Frequency
Calibration Data
Fig. 2.14
The TON (Transmitter ON) is a gate signal which functions to cut the carrier signal for non
signal period when transmitting the temperature, depth and catch monitor data. This control
helps to conserve battery consumption. However, in the transmission period of upward and
downward sounding data, the carrier signal is emitted even when there is no echo signal.
Refer to Fig.1.8 TX unit timing chart.
•
Power Amplifier
The output applied to the frequency divider is frequency-calibrated and FM-modulated
signals. The frequency divider divides the frequency by 8 to produce the actual transmitting
frequency of 33, 40 or 50kHz. A gate circuit is incorporated in the output of the frequency
divider to provide the dead time to prevent the two power transistors from conducting
simultaneously. The output of the frequency divider is sent to the power amplifier and
applied to the transducer. The output power is 10W or 2.4W as determined by tap
connections of the output transformer.
2-9
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