Circuit Description; Introduction; Pll Circuit; Receiver Circuit - Galaxy DX 959 Service Manual

CHAPTER 3
CIRCUIT
DESCRIPTION
DX 959

3.0 INTRODUCTION

This section explains the technical theory of operation for the Galaxy DX 959 mobile transceiver.

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,
Q27, Q28 and Q61. The PLL circuit is programmed by the user's rotary channel switch GPS-501.
The switch allows GPS-501 to communicate the correct binary data information to the
programmable divider inside of IC3. IC3 then controls the VCO (Voltage Controlled Oscillator),
consisting of VCO 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 receive signal come into the radio via the antenna and into the front end pre-amp
consisting of Q17. The RF signal is fed into the mixer circuit of the Q18 and then into the AM IF
section of the receiver (depending on the mode of operation). The signal is then detected by either
the AM detector or product detector and then fed to the audio amplifier section of the receiver and
finally out to the speaker.

3.3 TRANSMITTER MODULATION CIRCUIT

(i) 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 balanced modulator circuit.
(ii) If the transceiver is in the AM mode, the AF amplifier controls directly the RF amplifier gain of
the last RF amplifier which produces a true amplitude modulation RF signal.
(iii) If the transceiver is in the SSB mode, the audio signal is mixed with 10.6975MHz oscillator in
IC6.

3.4 TRANSMITTER AMPLIFIER CIRCUIT

The transmitter takes the basic exciter signal from the TX mixer and amplifies it through a series of
amplifiers consisting of Q50, Q51, Q49 and Q47 where it is sent out to the antenna connector.
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