Motorola GP series Service Manual

2-6 THEORY OF OPERATION
4.0 UHF Receiver (Models with PCB 8486686Z02)
The UHF receiver consists of a front and back end. A block diagram of the receiver is shown in
Figure 2-3. Detailed descriptions of these features are contained in the paragraphs that follow.
Figure 2-3 UHF Receiver Block Diagram.
4.1 Receiver Front-End
( Refer to Figure 2-3 and the UHF Receiver Front End schematic diagram for PCB 8486686Z02)
The RF signal is received by the antenna and applied to a low-pass filter. For UHF, the filter consists
of L101, L102, C102, C103, C104. The filtered RF signal is passed through the antenna switch. The
antenna switch circuit consists of two PIN diodes(CR101 and CR102) and a pi network (C106, L104
and C107).The signal is then applied to a varactor tuned bandpass filter. The UHF bandpass filter
comprises of L301, L302, C302, C303, C304, CR301 and CR302. The bandpass filter is tuned by
applying a control voltage to the varactor diodes(CR301 and CR302) in the filter.
The bandpass filter is electronically tuned by the DACRx from IC404 which is controlled by the
microprocessor. Depending on the carrier frequency, the DACRx will supply the tuned voltage to the
varactor diodes in the filter. Wideband operation of the filter is achieved by shifting the bandpass
filter across the band.
Crystal
Filter
Mixer
Varactor
Tuned Filter
RF Amp
Varactor
Tuned Filter
Pin Diode
Antenna
Switch
RF Jack
Antenna
Control Voltage
from ASFIC
First LO
from VCO
Second LO
IF Amp
455kHz
Filter
Switch
455kHz
Filter
455kHz
Filter
Switch
Demodulator
RSSI
Limiter
Recovered Audio
BW SEL
U301

Motorola GP series Specifications

General

Brand	Motorola
Model	GP series
Category	Radio
Language	English