Circuit Description; Introduction; Pll Circuit; Receiver Circuit - Galaxy DX 979 Service Manual

DX 979

3.0 INTRODUCTION

This section explains the technical theory of operation for the DX 979 mobile CB radio.

3.1 PLL CIRCUIT

The Phase Lock Loop (PLL) circuit is responsible for developing the receiver's first local oscillator
signal and the transmitter's exciter signal. The PLL circuit consists primarily of IC2, IC3, Q25, Q29
and Q28. The PLL circuit is programmed by the rotary channel switch GPS-668. The GPS-668
communicates the correct binary data information to the programmable divider inside of IC3. IC3 then
controls the VCO (Voltage Controlled Oscillator) to oscillate on the correct frequency. This signal is
fed either into the receiver's first mixer (for receive operation) or the transmitter's mixer (for transmit
operation).

3.2 RECEIVER CIRCUIT

The incoming RF signal comes into the radio via the antenna and into the front-end pre-amp, Q17. The
RF signal is fed into the mixer circuit of Q18/Q19 and then into the AM IF section of the receiver. The
signal is then detected by the AM detector and then fed to the audio amplifier section of the receiver
and finally out to the speaker.

3.3 TRANSMITTER MODULATION CIRCUIT

(1) The transmitter modulation circuit modulates the low-level RF signal from the PLL exciter circuit
with the user's audio voice signal from the microphone. The audio from the microphone is then
amplified and fed into the transmit amplifier circuit.
(2) If the transceiver is in the AM mode, the AF power amplifier modulates the last RF amplifier,
which produces a true amplitude modulated RF signal.
(3) If the transceiver is in the SSB mode, the audio signal is mixed with the 10.6975MHz oscillator in
IC6.

3.4 TRANSMITTER AMPLIFIER CIRCUIT

The transmitter takes the basic exciter signal from IC9 of the TX mixer and amplifies it through a series
of amplifiers consisting of Q52, Q51, Q49 and Q47 where it is sent out to the antenna connector.
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CHAPTER 3
CIRCUIT
DESCRIPTION