Motorola GP344 Detailed Service Manual

Receiver 1-3
3.0 Receiver
The UHF receiver consists of a front end, back end and automatic gain control circuits. A block
diagram of the UHF receiver is shown in Figure 2-2 .
3.1 Receiver Front-End
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.
The output of the bandpass filter is coupled to the RF amplifier transistor Q301 via C307. After being
amplified by the RF amplifier, the RF signal is further filtered by a second varactor tuned bandpass
filter, consisting of L306, L307, C313, C317, CR304 and CR305.
Figure 1-2 UHF Receiver Block Diagram
Demodulator
Synthesizer
Crystal
Filter
Mixer
Varactor
Tuned Filter
RF Amp
Varactor
Tuned Filter
Pin Diode
Antenna
Switch
RF Jack
Antenna
AGC
Control Voltage
from ASFIC
First LO
from FGU
Recovered Audio
Squelch
RSSI
IF
IC
SPI Bus
16.8 MHz
Reference Clock
Second
LO VCO
IF Amp
U301

Motorola GP344 Specifications

General

power supply	7.5 V
power VHF	1-5 W
power UHF 1	1-4 W
power UHF 2	1-4 W
average battery life with standard Li-lon battery (low power)	>9 hours
average battery life with standard Li-lon battery (high power)	>7 hours
average battery life with high capacity Li-lon battery (low power)	>13 hours
average battery life with high capacity Li-lon battery (high power)	>10 hours
operating temperature	-20°C to +55°C
frequencies VHF	136-174 MHz
frequencies UHF 1	403-470 MHz
frequencies UHF 2	450-527 MHz
channel spacing	12.5/20/25 kHz
frequency stability	±2.5 ppm
modulation limiting @ 12.5 kHz	±2.5
modulation limiting @ 20 kHz	±4.0
modulation limiting @ 25 kHz	±5.0
FM hum & noise	-40 dB typical
conducted/radiated emission <1 GHz	-36 dBm
conducted/radiated emission >1 GHz	-30 dBm
audio response (300-3000Hz)	+1 to -3 dB
audio distortion	<5% typical
frequencies VHF	136-174 MHz
frequencies UHF 1	403-470 MHz
frequencies UHF 2	450-527 MHz
channel spacing	12.5/20/25 kHz
sensitivity (12 dB SINAD) EIA	0.35 µV typical
intermodulation EIA	-65 dB
adjacent channel selectivity @ 12.5 kHz	60 dB
adjacent channel selectivity @ 20/25 kHz	70 dB
spurious rejection	70 dB
rated audio	0.5W
audio response (300-3000 Hz)	+1 to -3 dB

Weight and Dimensions

dimensions with standard Li-lon battery	101.5 x 55.5 x 30.5 mm
dimensions with high capacity Li-lon battery	101.5 x 55.5 x 35.5 mm
weight with standard Li-lon battery	250 gm
weight with high capacity Li-lon battery	270 gm