Introduction; Pll Circuit; Receiver Circuit; Transmitter Modulation Circuit - Ranger RCI-2985DX Manual

5.0 INTRODUCTION

This section explains the technical theory of operation for the RCI-2985DX / RCI-2995DX Amateur 10
and 12 meter dual band base station transceiver.

5.1 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, Q29, Q32,
Q33, Q34, Q36, Q37, Q38 and L16. The PLL circuit is programmed by the rotary channel switch GPS-
0751. The switch allows IC (U601) on CPU PCB to communicates the correct binary data information
to the programmable divider inside of IC2. IC2 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).

5.2 RECEIVER CIRCUIT

The incoming RF signal comes into the radio via the antenna and into the front-end pre-amp, Q19. The
RF signal is fed into the mixer circuit of Q20 and Q21. The signal is then filtered by L8, L9 and L10
then into the AM/FM IF section of the receiver (depending on the mode of operation). The signal is
then detected by either the AM detector or FM detector and then fed to the audio amplifier section of
the receiver and finally out to the speaker.

5.3 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 balanced modulator 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 FM mode, the audio signal is not mixed with 10.6975MHz oscillator but
instead phase modulates the basic exciter signal from the PLL circuit in the TX mixer.
(4) If the transceiver is in the SSB mode, the audio signal is mixed with the 10.6975MHz oscillator in
IC5.

5.4 TRANSMITTER AMPLIFIER CIRCUIT

The transmitter takes the basic exciter signal from the TX mixer and amplifies it through a series of
amplifiers consisting of Q64, Q63, Q62, Q61, Q60 and EPA010010B (only for RCI-2995DX) where it
is then sent out to the antenna connector.
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