Motorola GP340 Service Information

2-4 THEORY OF OPERATION
Both the pre and post-RF amplifier varactor tuned filters have similar responses. The 3dB bandwidth
of the filter is about 50 MHz. This enables the filters to be electronically controlled by using a single
control voltage which is DACRx .
The output of the post-RF amplifier filter which is connected to the passive double balanced mixer
consists of T301, T302 and CR306. Matching of the filter to the mixer is provided by C381. After
mixing with the first LO signal from the voltage controlled oscillator (VCO) using low side injection,
the RF signal is down-converted to the 45.1 MHz IF signal.
The IF signal coming out of the mixer is transfered to the crystal filter (FL301) through a resistor pad
and a diplexer (C322 and L310). Matching to the input of the crystal filter is provided by C324 and
L311. The crystal filter provides the necessary selectivity and intermodulation protection.
3.2 Receiver Back-End
(Refer to Figure 2-2 and the Receiver Back-End schematic diagram)
The output of crystal filter FL301 is matched to the input of IF amplifier transistor Q302 by
components R352 and C325. Voltage supply to the IF amplifier is taken from the receive 5 volts
(R5). The IF amplifer provides a gain of about 7dB. The amplified IF signal is then coupled into
U301(pin 3) via C330, C338 and L330 which provides the matching for the IF amplifier and U301.
The IF signal applied to pin 3 of U301 is amplified, down-converted, filtered, and demodulated, to
produce the recovered audio at pin 27 of U301. This IF IC is electronically programmable, and the
amount of filtering (which is dependent on the radio channel spacing) is controlled by the
microprocessor. Additional filtering, once externally provided by the conventional ceramic filters, is
replaced by internal filters in the IF module (U301).
The IF IC uses a type of direct conversion process, whereby the externally generated second LO
frequency is divided by two in U301 so that it is very close to the first IF frequency. The IF IC (U301)
synthesizes the second LO and phase-locks the VCO to track the first IF frequency. The second LO
is designed to oscillate at twice the first IF frequency because of the divide-by-two function in the IF
IC.
In the absence of an IF signal, the VCO will “search” for a frequency, or its frequency will vary close
to twice the IF frequency. When an IF signal is received, the VCO will lock onto the IF signal. The
second LO/VCO is a Colpitts oscillator built around transistor Q320. The VCO has a varactor diode,
CR310, to adjust the VCO frequency. The control signal for the varactor is derived from a loop filter
consisting of C362, C363, C364, R320 and R321.
The IF IC (U301) also performs several other functions. It provides a received signal-strength
indicator (RSSI) and a squelch output. The RSSI is a dc voltage monitored by the microprocessor,
and used as a peak indicator during the bench tuning of the receiver front-end varactor filter. The
RSSI voltage is also used to control the automatic gain control (AGC) circuit at the front-end.
The demodulated signal on pin 27 of U301 is also used for squelch control. The signal is routed to
U404 (ASFIC) where squelch signal shaping and detection takes place. The demodulated audio
signal is also routed to U404 for processing before going to the audio amplifier for amplification.

Motorola GP340 Specifications

Power and Battery

power supply	Rechargeable Battery 7.5v
battery life with standard high capacity NiMH battery (low power)	11 hours
battery life with standard high capacity NiMH battery (high power)	8 hours
battery life with ultra high capacity NiMH battery (low power)	14 hours
battery life with ultra high capacity NiMH battery (high power)	11 hours
battery life with NiCD battery (low power)	12 hours
battery life with NiCD battery (high power)	9 hours
battery life with Li-lon battery (low power)	11 hours
battery life with Li-lon battery (high power)	8 hours

Operating Environment

operating temperature	-20°C to +55°C
sealing	Withstands rain testing per MIL STD 810 C/D/E and IP54
shock and vibration	Protection provided via impact resistant housing exceeding MIL STD 810-C/D/E and TIA/EIA 603
dust and humidity	Protection provided via environment resistant housing exceeding MIL STD 810 C/D/E and TIA/EIA 603

Transmitter Specifications

frequencies - full bandsplit	VHF: 136-174 MHz, LB1: 29.7-42 MHz, UHF: 300-350 MHz, LB2: 35-50 MHz, UHF1: 403-470 MHz
channel spacing	12.5/20/25 kHz
frequency stability	±2.5 ppm
power	136-174: 1-5W, 300-350: 1-4W, 403-470: 1-4W
modulation limiting	±2.5 @ 12.5 kHz, ±4.0 @ 20 kHz, ±5.0 @ 25 kHz
FM hum & noise	-40dB typical
conducted/radiated emission	-36 dBm <1 GHz, -30 dBm >1GHz
adjacent channel power	-60 dB @ 12.5 kHz, -70 dB @ 20/25 kHz
audio response (300-3000Hz)	+1 to -3 dB
audio distortion	3%

Receiver Specifications

frequencies - full bandsplit	VHF: 136-174 MHz, LB1: 29.7-42 MHz, UHF: 300-350 MHz, LB2: 35-50 MHz, UHF1: 403-470 MHz
channel spacing	12.5/20/25 kHz
sensitivity (12 dB SINAD) EIA	.25µV typical
sensitivity (20 dB SINAD) EN	.50µV typical
intermodulation EIA	70 dB
adjacent channel selectivity	60 dB @ 12.5 kHz, 70 dB @ 20/25 kHz
spurious rejection	70 dB
rated audio	0.5W
audio distortion @ rated audio	3% typical
hum & noise	-40 dB @ 12.5 kHz, -50 @ 20/25 kHz
audio response (300-3000 Hz)	+1 to -3 dB
conducted spurious emission	-57 dBm <1 GHz, -47 dBm <1 GHz

Weight and Dimensions

dimensions with standard high capacity NiMH battery	137 x 57.5 x 37.5 mm
dimensions with ultra high capacity NiMH battery	137 x 57.5 x 40.0 mm
dimensions with NiCD battery	137 x 57.5 x 40.0 mm
dimensions with Li-lon battery	137 x 57.5 x 33.0 mm
weight with standard high capacity NiMH battery	420 gm
weight with ultra high capacity NiMH battery	500 gm
weight with NiCD battery	450 gm
weight with Li-lon battery	350 gm