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3.0 INTRODUCTION
This section explains the technical theory of operation for the Galaxy DX 2547 Base Station
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, Q29
and Q28. The PLL circuit is programmed by the rotary channel switch GPS-0501. The GPS-0501
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 dual mosfet mixer circuit of Q18/Q19 and then into the AM/SSB 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 transmit amplifier circuit.
(ii) 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.
(iii) 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 the TX mixer and amplifies it through a series of
amplifiers consisting of Q52, Q51, Q49 and Q47 where it is then sent out to the antenna connector.
Summary of Contents for DX 2547
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