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THEORY OF OPERATION
Ray54/E For Raymarine
2004 Feb 27
This PLL controlled VHF marine mobile transceiver provides an accurate and stable multi-channel
operation.
The transceiver consists of 13 main sections
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Transmitting stage
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Receiving stage
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Local oscillator PLL (Phase Lock Loop) Circuit
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Memory backup
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Low voltage detection
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Large LCD
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Local/distance Circuit
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2nd Receiver
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WX Alert Circuit (only USA)
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PC Program
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DSC Feature
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GPS Message
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ATIS Feature (only EU)
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Transmitter Stage
The audio is picked up from the internal Mic. The audio signal is then amplified by Audio Amplifier, IC205C ,
IC205B and filtered by a low pass filter IC10C, IC10D. The audio that is adjusted by VR3 to obtain a
suitable RF frequency-deviation, modulates the carrier of VCO, through Varicap (VD302).
The modulated signal output from the VCO is pre-amplified by Q2, and IC1 . When the supply voltage is
13.6V, this signal will be amplified up to 1W or 25W. The signal is filtered by low-pass filter circuit of which
consists of L1, L2, L4, C1, C2, C3, C5, C6, C14, C47 and C62.These low pass filters are necessary to
suppress the second and the third harmonics as higher. The signal is then fed into the antenna input and
radiated out. The signal is also fed into another path consisting of C9, C10, D3, D4 for sampling, and is
converted into a direct current voltage for the Automatic Power Control (APC) circuit IC12, Q5, Q14, Q15,
Q24 to control the voltage of IC1 Pin 2 to maintain the output power stability. Q15 is used control Hi/Lo
power
When the unit is transmitting, the channel control voltage is added to the TX VCO varicap VD306. The
capacitance of VD302 is varied following the audio signal, therefore the carrier is modulated to form the
modulated signal.
