In the event that the lock state is not obtained, the logic circuit automatically inhibits the transmitter to prevent
The transmitter is designed for operation in the VHF Marine frequency range of 156 - 158 MHz.
The audio signal originated at the microphone is applied to a microphone amplifier circuit consisting of a high pass filter,
a microphone amplifier, a 6 dB pre-emphasis network, instantaneous deviation control (I.D.C.), and a low pass filter.
The amplified audio signal is fed to the PLL frequency synthesizer to obtain an FM modulated RF signal.
Small Signal Stage
The modulated RF carrier output from the PLL frequency synthesizer is applied to the RF amplifier stages (Q501
The RF signal from the small signal stage is fed to a power amplifier stage consisting of a pre-driver (Q503), driver
(Q504), and final transistor (Q505).
Output Filter/Matching Network
The transmit signal, having been amplified by the power stage, is fed through a four-stage filter network to remove
unwanted signals and to in- sure proper matching to the antenna. This section also includes a solid- state antenna
switching circuit to supply the signals received at the antenna to the receiver circuit, and an RF power sensor to
send information to the power control circuit.
Power Control Circuit
The DC signal which is sent from the sensor causes a voltage regulator to respond, levelling the transmitter output power
and, if high VSWR is present in the antenna line, automatically reducing the power to a safe operating level. The output
power in high and low modes are individually adjustable.
The receiver is a double conversion superheterodyne designed for operation in the VHF Marine frequency range of
The RF signal is picked up at the antenna and fed into a two-stage bandpass