Motorola Gp68 Part1 6881086c09 O Manual

 
March, 1997 6881086C09-O
 
2-1
 
Section 2
Theory of Operation 
Overview 
This section provides a detailed theory of operation for the
GP60 Series Radios and its components.
The GP60 Series radio consists three main boards; Control-
ler board, rf board and display board. The controller board is
connected to the rf board through a 20 lines flex ribbon cable.
The display board is connected to the controller board
through a 14 pins board-to-board connector. The top key
pads are embedded on a flex that makes...

 
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Theory of OperationGP68 Portable Radios Service Manual
Transmit and Receive Audio Circuitry
 
Tx Audio Path 
Internal PTT, MIC Bias Switch and External PTT 
Sense Circuits  
The internal PTT switch (SW402) is connected direct to the
input port of the microcomputer (pin 42) to ground. This port
is an active low. One of the R415 resistor is used to pull up
the line to 5 volt. While PTT (internal) this line will be pulled
low. Internal MIC bias is supplied from the +5VTX...

 
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GP68 Portable Radios Service ManualTheory of Operation 
Transmit and Receive Audio Circuitry
 
path must settle within 1 millisecond of PTT activation to
prevent center frequency offset. 
Rx Audio Path 
Audio Processing (Audio Filter IC)  
The recovered Rx audio from the rf board (IF detector IC
U51) is coupled through to U451-7 and U451-8 on the Audio
Filter IC. Rx audio at U451-7 is processed first by the PL
rejection filter, which is characterized by a 2-pole, 300 Hz...

 
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Theory of OperationGP68 Portable Radios Service Manual
 
Adaptive Power Control
 
TM
 
 Technology
 
J403-6 
J403-6 is interfaced to pin 4 of voltage regulator U456. This
is the microprocessors 5 V source from the main board to the
option board. Maximum current sourcing is 100 mA. Regu-
lation is  
± 
0.2 Vdc.  
J403-7 
J403-7 interfaces with pin 52 of U401. Pin 52 of the micro-
controller is bi-directional port D bit 3. In the GP60 Series
Radio, this connection is for...

 
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GP68 Portable Radios Service ManualTheory of Operation 
RF Board
 
have difficulty to source high current (2.1 ampere at 5 watts
operation). If there are forced to do so, the voltage will drop
and when the voltage hits 5 volts, the radio will automati-
cally reset by it self. It means the batteries cannot be used at
all for transmitting even though there are still a lot of power
inside the batteries. With this circuitry, the user will be able
to enjoy the radio operation...

 
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Theory of OperationGP68 Portable Radios Service Manual
Transmitter
 
second LO, the second IF, and the IF IC chip. The first LO
signal and the RF signal mix to the IF frequency (45.1 MHz
for VHF and 73.35 MHz for UHF) which then enters the IF
portion of the radio.
The signal first enters the high IF, passes through a crystal fil-
ter and is then amplified by the IF amp. The crystal filter pro-
vides selectivity, second image protection, and
intermodulation protection. The...

 
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GP68 Portable Radios Service ManualTheory of Operation 
The GP60 Series Radio Alignment Procedures
 
In addition to the VCO, the synthesizer must interface with
the logic and AFIC circuitry. Programming for the synthe-
sizer is accomplished through the data, clock, and chip
enable lines (pins 5, 6, and 7) which are driven by the micro-
processor, U401. A serial stream of 98 bits is sent whenever
the synthesizer is programmed. A 5 Volt dc signal from pin 2
of U201...

 
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Theory of OperationGP68 Portable Radios Service Manual
The GP60 Series Radio Alignment Procedures
 
Low Port Modulation 
Tuning Frequency: 
Automatic - Frequency displayed on Tuning screen. 
Deviation Setting: 
375 Hz +/- 40 Hz for 12.5 kHz channel spacing,
750 Hz +/- 40 Hz for 20/25/30 kHz channel spacing.
•Set the radio into TX low power mode. The Modula-
tion Analyzer should be set as follows:
•Use the up/down arrow keys to change the low port
deviation setting and...

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Squelch Attenuator
Rx Filter
Tone
Generator
Lowspeed
Generator
Deviation
Attenuator
Splatter
FilterLimiter
De-emphasis
5 Volt
Regulator
Audio
PA
Volume
PA Enable
Speaker
Mic Enable
Mic
PreampliÞer Pre-
Highspeed
Data
Generator
Channel
Switch
Push
Buttons Lowspeed
Control
Battery
MonitorFrom
BatterySCI BUS
Harmonic
FilterReceiver1st
MixerIF2nd Mixer
Demodulator
Synthesizer
VCOReference
Oscilator
RF
PA
Analog
Control
Steering/
VCO
ModWarp
Prescaler
Squelch Adjust
Rx
Audio...

 
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6881086C09-O March, 1997
 
     
 RECEIVER  BLOCK  DIAGRAM 
IF 
Amp 
2-Pole
Crystal
 Filter
15+ Lo  +6dbm     
     RF
Amp    2-Pole
Bandpass
    Filter     Filter  Bandpass     3-Pole
Detected  audio From
Antenna
Switch
 5V RX5V RX
 
2nd LO 
4-Pole
Ceramic 4-Pole
Ceramic 
 TRANSMITTER BLOCK DIAGRAM 
Pin +5V Tx
Pre-driver
Driver
 
TX B+
Final
CouplerAntenna
    SwitchHarmonic
  Filter
 Power 
ControlTo Receiver
 
IF IC  
Buffer
VCTL
B+
IDAC 
Block Diagram for Receiver and Transmitter