Motorola MCS 2000 Operating instructions

68P81080C44-B, Issued 5/98
MCS 2000 Mobile Radio
Service Instructions
Volume 2d
900-MHz Frequency Range Specific
 1998 by Motorola, Inc., Radio Network Solutions Group
8000 West Sunrise Boulevard
Ft. Lauderdale, FL 33322

Safety 0 Revision B, 5/98
Safety Information
Every radio, when transmitting, radiates energy into the atmosphere which
may, under certain conditions, cause the generation of a spark.
All users of vehicles fitted with radios should be aware of the following
warnings:
Do not operate radio near flammable liquids or in the vicinity of explosive
devices.
To ensure personal safety, please observe the following simple rules:
Check the laws and regulations on the use of two-way mobile radios in the
areas where you drive. Always obey them. Also, when using your radio while
driving, please:
• Give full attention to driving,
• Use hands-free operation, if available and
• Pull off the road and park before making or answering a call if driving
conditions so require.
Airbag
Warning
Installation of vehicle communication equipment should be performed by a
professional installer/technician qualified in the requirements for such
installations.
An air bag’s size, shape and deployment area can vary by vehicle make, model
and front compartment configuration (e.g., bench seat vs. bucket seats).
Contact the vehicle manufacturer’s corporate headquarters, if necessary, for
specific air bag information for the vehicle make, model and front
compartment configuration involved in your communication equipment
installation.
LP Gas
Warning
It is mandatory that radios installed in vehicles fuelled by liquefied petroleum
gas conform to the National Fire Protection Association standard NFPA 58,
which applies to vehicles with a liquid propane (LP) gas container in the trunk
or other sealed off space within the interior of the vehicle. The NFPA58
requires the following:
• Any space containing radio equipment shall be isolated by a seal from the
VEHICLES EQUIPPED WITH AIR BAGS
An air bag inflates with great force. DO NOT place objects, including
communication equipment, in the area over the air bag or in the air bag
deployment area. If the communication equipment is improperly
installed and the air bag inflates, this could cause serious injury.

Revision B, 5/98 Safety 1
space in which the LP gas container and its fittings are located.
• Removable (outside) filling connections shall be used.
• The container space shall be vented to the outside.
Anti-Lock Braking System (ABS) and
Anti-Skid Braking System Precautions
Disruption of the anti-skid/anti-lock braking system by the radio
transmitter may result in unexpected vehicle motion.
Motorola recommends the following radio installation precautions and
vehicle braking system test procedures to ensure that the radio, when
transmitting, does not interfere with operation of the vehicle braking system.
Installation Precautions
1. Always provide as much distance as possible between braking modulator
unit and radio, and between braking modulator unit and radio antenna
and associated antenna transmission line. Before installing radio,
determine location of braking modulator unit in vehicle. Depending on
make and model of vehicle, braking modulator unit may be located in
trunk, under dashboard, in engine compartment, or in some other cargo
area. If you cannot determine location of braking modulator unit, refer
to vehicle service manual or contact a dealer for the particular make of
vehicle.
2. If braking modulator unit is located on left side of the vehicle, install
radio on right side of vehicle, and conversely.
3. Route all radio wiring including antenna transmission line as far away as
possible from braking modulator unit and associated braking system
wiring.
4. Never activate radio transmitter while vehicle is in motion and vehicle
trunk lid is open.
Braking System Tests
The following procedure checks for the most common types of interference
that may be caused to vehicle braking system by a radio transmitter.
1. Run vehicle engine at idle speed and set vehicle transmission selector to
PARK. Release brake pedal completely and key radio transmitter. Verify
that there are no unusual effects (visual or audible) to vehicle lights or
other electrical equipment and accessories while microphone is NOT
being spoken into.
2. Repeat step 1. except do so while microphone IS being spoken into.
3. Press vehicle brake pedal slightly just enough to light vehicle brake
light(s). Then repeat step 1. and step 2.
4. Press the vehicle brake pedal firmly and repeat step 1. and step 2.
5. Ensure that there is a minimum of two vehicle lengths between front of
vehicle and any object in vehicle’s forward path. Then, set vehicle
!
W A R N I N G
!

Safety 2 Revision B, 5/98
transmission selector to DRIVE. Press brake pedal just far enough to stop
vehicle motion completely. Key radio transmitter. Verify that vehicle
does not start to move while microphone is NOT being spoken into.
6. Repeat step 5. except do so while microphone IS being spoken into.
7. Release brake pedal completely and accelerate vehicle to a speed between
15 and 25 miles/25 and 40 kilometers per hour. Ensure that a minimum
of two vehicle lengths is maintained between front of vehicle and any
object in vehicle’s forward path. Have another person key radio
transmitter and verify that vehicle can be braked normally to a moderate
stop while microphone is NOT being spoken into.
8. Repeat step 7. except do so while microphone IS being spoken into.
9. Release brake pedal completely and accelerate vehicle to a speed of 20
miles/30 kilometers per hour. Ensure that a minimum of two vehicle
lengths is maintained between front of vehicle and any object in
vehicle’s forward path. Have another person key radio transmitter and
verify that vehicle can be braked properly to a sudden (panic) stop while
microphone is NOT being spoken into.
10. Repeat step 9. except do so while microphone IS being spoken into.
11. Repeat step 9. and step 10. except use a vehicle speed of 30 miles/50
kilometers per hour.

Revision B, 5/98 List of Effective Pages A
LIST OF EFFECTIVE PAGES
MCS 2000 Mobile Radio Service Instructions
Volume 2d
900-MHz Frequency Range Specific Information
Motorola Publication Number 68P81080C44-B
I ssue Dates of Original and Revised Pages are:
Revision O: March 1996
Revision A: November 1996
Revision B: May 1998
The Number of pages in this publication is 104 consisting of the
following:
Note: The letter O in the Revision Letter column of the table above denotes an original page. Original pages
ARE NOT identified as such in the page footors except by the absence of a change letter and date.
Page Number Revision Letter Page Number Revision Letter
Front cover O 1 through 90 B
Inside front cover (blank) O Questionnaire (Front) O
Title B Questionnaire (Back) O
Safety 0 through
Safety 2 B Inside Back Cover (Replacement Parts
Ordering)
B
A and B B Back Cover (Not
Markedwith Revision
Letter
A
i and ii B

B Revision B, 5/98
NOTES

Revision B, 5/98 Table of Contents i
Table of Contents
- Safety Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Safety 0
- List of Effective Pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A
- List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
- List of Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
1- Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
2- Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Block Diagram Level Theory of Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Receiver Detailed Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Transmitter Detailed Functional Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Synthesizer Detailed Functional Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Controller Detailed Functional Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Dc Power Control and Regulation Detailed Functional Description. . . . . . . . . . . . . . . . . . . . . . . 17
3 - Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
4 - Reference Drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

ii List of Figures/List of Tables Revision B, 5/98
List of Figures/List of Tables
Figure 1. 900-MHz Radio Functional Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 2. Transceiver Board Section Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
Note : Troubleshooting charts are listed on page 19; Component location illustrations, schematic dia-
grams, and parts lists are listed on page 33 .
List of Tables
Table 1. Transceiver Board Kit Numbers v.s. Service Manual Page Numbers for
Specific Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Table 2. Schematic Diagrams Interconnection List. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Revision B, 5/98 Introduction 1
Introduction 1
This publication (Service Manual Volume 2d, Motorola Publication
68P81080C44) provides frequency-range-specific information for the
12-Wattand30-WattMCS2000radiosforwhichthetransceiverboard
kit numbers are listed in Table 1. These radios all operate in the 900-
MHz frequency range. The coverage in this publication includes both
non-data-capable and data-capable radios.
This publication is a companion volume to Service Manual Volume 1
for MCS 2000 Radios, Motorola Publication 68P81083C20, which
provides non-frequency-range-specific information for all MCS 2000
Radios. Service personnel must have both Volume 1 and Volume 2a of
this Service Manual in order to have all service information for
12-Watt and 30-Watt MCS 2000 Radios that operate in the 900-MHz
frequency range.
There are other Volume 2 service manuals (e.g., Volume 2a, 2b, 2c),
which cover models of the MCS 2000 Radio for other frequency ranges
and power levels. Refer to Volume 1 of this service manual for a list of
the manuals related to operation and maintenance of all models of the
MCS 2000 Radio, and the Motorola publication numbers for those
manuals.
Hereafter in this manual, the MCS 2000 Radio is referred to as the
radio. The specific hardware portions of the radio covered in this
volume of the service manual are as follows:
• Receiver Front End
• Receiver Intermediate Frequency (IF)
• Receiver Back End
• 12-Watt Power Amplifier
• 30-Watt Power Amplifier
• Synthesizer
This volume (Volume 2d) of the service manual covers the following
five topics for the specific hardware portions of the 900-MHz radios:
• Theory of operation
• Troubleshooting
• Component locations
• Parts lists

2 Introduction Revision B, 5/98
• Schematic diagrams and associated interconnect information
The five topics listed above for the controller section and for the
control heads are covered in Volume 1 of this service manual,
Motorola Publication Number 68P81083C20.
All the radios covered in this service manual contain a single circuit
card assembly (a printed circuit board with components mounted),
which is called the transceiver board. The transceiver board in each
version of the radio is identified by a unique Motorola kit number
(e.g., FLF5591A). The kit number varies according to the RF output
power level of the radio (12-Watts or 30-Watts) and also according to
whether or not the radio is data capable. Table 1 on pages 3 and 4
crossreferences each kit number covered in this service manual to the
page number where the specified information is located.

Revision B, 5/98 3
Table 1: Transceiver Board Kit Numbers v.s. Service Manual Page Numbers for Specific Information
Kit
Number
RF
Power
Level
Printed Circuit Board (PCB) Functional
Sections
Intercon-
nection
Information
Controller Receiver Front End (Page No.) Receiver Intermediate Frequency (IF) (Page No.)
Part No.
Functional
Section
Locations
(Page No.)
Main
Controller
Section
Power
Control
Section
Theory of
Operation
Trouble
shooting
Chart
Component
Locations
and Parts
List
Schematic
Diagram Theory of Operation
Trouble
shooting
Chart
Component
Locations
and Parts
List
Schematic
Diagram
FLF5591A, B, C
Not Data
Capable
12
8404416P04
Issue P4 34 59
Refer to
Service
Manual
Volume 1
Motorola
Publication
68P81083C20
Refer to
Service
Manual
Volume 1
Motorola
Publication
68P81083C20
92536379263839
FLF5592A, B, C
Not Data
Capable
30
8404994E05
Issue P5 34 59
92536379263839
FLF5604A
Data Capable
12
8408559Y01
Issue P1 34 59
925363710264041
FUF5752A
Data Capable
30
8486005J01
Issue P1 34 59
925363710264041
FLF5952A
Data Capable
12
8408497Y01
Issue P2 34 59
925363710264041
FLF5606A
Data Capable
30
8408597Y01
Issue P2 34 59
925363710264041
HUF1190A
Not Data
Capable
12 8404416P05
Issue P5 34 59
92536379263839
HUF1191A
Not Data
Capable
30 8404994E05
Issue P5 34 59
92536379263839

4 Revision B, 5/98
Table 1: Transceiver Board Kit Numbers v.s. Service Manual Page Numbers for Specific Information (Continued)
Kit
Number
RF
Power
Level
Printed
Circuit Board
(PCB) Part
No.
Receiver Back End (Page No.) Synthesizer (Page No.) Power Amplifier (PA) (Page No.)
Theory of
Operation
Trouble
shooting
Chart
Parts List
and
Component
Locations
Schematic
Diagram Theory of Operation
Trouble
shooting
Chart
Parts List
and
Component
Locations
Schematic
Diagram Theory of Operation
Trouble
shooting
Chart Repair
Parts List
and
Component
Locations
Schematic
Diagram
FLF5591A, B, C
Not Data
Capable
12
8404416P04
Issue P4
11 26 42 43 15 27 thru 30 56 57 12 31 N/A 48 49
FLF5592A, B, C
Not Data
Capable
30
8404994E05
Issue P5
11 26 42 43 15 27 thru 30 56 57 14 32 20 50 51
FLF5604A
Data Capable
12
8408559Y01
Issue P1
11 26 42 45 15 27 thru 30 56 57 12 31 N/A 48 49
FUF5752A
Data Capable
30
8486005J01
Issue P1
11 26 42 45 15 27 thru 30 56 57 14 32 20 52 53
FLF5952A
Data Capable
12
8408497Y01
Issue P2
11 26 42 45 15 27 thru 30 56 57 12 31 N/A 50 51
FLF5606A
Data Capable
30
8408597Y01
Issue P2
11 26 42 45 15 27 thru 30 56 57 14 32 20 54 55
HUF1190A
Not Data
Capable
12 8404416P05
Issue P5
11 26 42 47 15 27 thru 30 56 57 12 31 N/A 48 49

Revision B, 5/98 Theory of Operation 5
Theory of
Operation 2
This chapter provides theory of operation information for the radio. It
starts with a block diagram level functional description of the entire
radio. This is followed by a detailed functional description for each of
the four major functions of the radio.
Introduction
The radio is composed of the following four major functions:
• Receiver
• Transmitter
• Dc Power Control and Regulation
• Operator Interface (Control Head)
The receiver, transmitter, and dc power control and regulation
functions are all located on a single circuit card assembly (CCA) in the
main body of the radio. The CCA is called the transceiver board. The
operator interface function consists of the control head, which plugs
into the main body of the radio. There are three different control head
types: the Model I for the Model I Radio; the Model II for the Model II
Radio; and the Model III for the Model III Radio. The three control
heads are covered in their entirety in Volume 1 of this service manual.
The transceiver board in the main body of the radio is physically
separated into six functional sections as follows:
• Receiver Front End
• Receiver Intermediate Frequency (IF)
• Receiver Back End
• Power Amplifier (PA)
• Synthesizer
• Controller
The controller section is further divided into two sub-sections: main
controller; and power control. The mechanical layout of the
transceiver board is illustrated in Chapter 4.
Separate component location diagrams, parts lists, and schematic
diagrams are provided in this service manual for each of the six
physical sections of the transceiver board and for the control heads.

6 Theory of Operation Revision B, 5/98
The component location diagrams, parts lists, and schematic diagrams
for the controller section of the transceiver board and for the three
types of control heads are located in Volume 1 of this service manual.
The component location diagrams, parts lists, and schematic diagrams
for the other five physical sections of the transceiver board are located
in this volume (Volume 2d).
Block Diagram
Level Theory of
Operation
The following discussion refers to the functional block diagram for the
radio, Figure 1.
Thereceiver function of the radio detects, demodulates, amplifies, and
outputs via the loudspeaker, radio signals picked up by the vehicle or
fixed-stationantenna. The radio signal input reaches the receiver from
the antenna via the antenna switch, which is located in the transmit-
ter function of the radio. The radio signals picked up by the antenna
are signals that have been re-broadcast by trunked or conventional
repeaters,orthathavebeenbroadcastdirectlybyothermobileorfixed
station radios.
The receiver function of the radio consists of: the receiver front end
section; the receiver intermediate frequency (IF) amplifier section; the
receiver back end section; and the audio signal filter (ASFIC) and
receiver audio power amplifier circuits in the controller section.
The receiver function of the radio uses the double conversion super-
heterodyne design to optimize image rejection and selectivity. The
receiver front end section converts the receiver input signal to a first
IF of 73.35 MHz. The frequency upon which the receiver operates is
determined by a first local oscillator signal generated by the synthesiz-
er section. For the purpose of this discussion, the synthesizer section is
considered to be part of the transmitter function of the radio.
The 73.35 MHz IF output signal from the receiver front end section
passes through the receiver IF amplifier section where it is filtered and
amplified. The output of the receiver IF amplifier section goes to the
receiver back end section. In the receiver back end section, which
contains the zero intermediate frequency (ZIF) integrated circuit (IC),
the receiver IF signal is demodulated to produce receiver audio and
squelch signals.
The receiver audio and squelch signal outputs from the receiver back
end section are processed by the audio signal filter integrated circuit
(ASFIC)in the controller section of the radio to generatereceiveraudio
(filtered) and squelch detect signals. The filtering characteristics and
other processes of the ASFIC are controlled by the central processor
unit in the controller section.
The receiver audio signal (filtered) from the output of the ASFIC goes
to the input of the receiver audio power amplifier circuit, which is
located in the controller section of the radio. The receiver audio power
amplifier circuit does not pass the receiver audio signal to the loud-
speaker until it receives an audio PA enable signal from the controller
section of the radio. The reason is that the receiver portion of the radio
includes a squelch function, which prevents receiver noise from pass-
ing to the loudspeaker during periods of no signal reception.

Revision B, 5/98 Theory of Operation 7
RECEIVER
RECEIVE
RF SIGNAL
RECEIVE RF SIGNAL
RECEIVER
FRONT END
SECTION
RECEIVER IF
AMPLIFIER
SECTION
RECEIVER
AUDIO AUDIO
SIGNAL
FILTER
(ASFIC)
AUDIO PA
ENABLE
SQUELCH
DETECT
RECEIVER
AUDIO RECEIVER
AUDIO
POWER
AMPLIFIER
RECEIVER
BACK END
SECTION
(ZERO IF) SQUELCH
FIRST
RECEIVER
LOCAL
OSCILLATOR
2.1 MHz
REFERENCE
OSCILLATOR
IF
73.35 MHz IF
73.35 MHz
LOUDSPEAKER
P/O CONTROLLER SECTION (NOTE 1)
DC POWER CONTROL AND REGULATION
13.8VDC
FROM VEHICLE
BATTERY OR
BASE STATION
POWER SUPPLY
CONTROL AND
REGULATION
CIRCUITS
REGULATED
DC POWER
P/O CONTROLLER SECTION
(NOTE 1)
TO TRANSCEIVER BOARD AND
CONTROL HEAD CIRCUITS
P/O CONTROLLER
SECTION
(NOTE 1)
AUDIO
SIGNAL
FILTER
(ASFIC)
AUDIO
MODULATION
SIGNAL SYNTHESIZER
SECTION
MEMORY
FEEDBACK
CONTROL
SB9600
DATA BUS
ACCESSORY
INPUTS AND
OUTPUTS
CENTRAL
PROCESSOR
UNIT (CPU)
SUPPORT
LOGIC
(SLIC)
RF POWER
AMPLIFIER
TRANSMIT
RF SIGNAL ANTENNA
SWITCH
ANTENNA
TRANSMITTER POWER AMPLIFIER SECTION
FIRST RECEIVER
LOCAL OSCILLATOR,
2.1 MHz
REFERENCE OSCILLATOR
TRANSMITTER
INJECTION
SIGNAL SERIAL
PERIPHERAL
INTERFACE
(SPI) BUS
AUDIO PA
ENABLE
TRANSMITTER
MICROPHONE
PUSH TO
TALK (PTT)
OPERATOR
KEYBOARD,
PUSHBUTTONS,
AND OTHER
CONTROLS
MICROPHONE
AUDIO
CONTROL HEAD
PROCESSOR OPERATOR
DISPLAY
DISPLAY DATA
1. REFER TO VOLUME 1 OF THIS
SERVICE MANUAL FOR INFORMATION
ABOUT CONTROLLER SECTION
NOTES:
2. REFER TO VOLUME 1 OF THIS
SERVICE MANUAL FOR INFORMATION
ABOUT CONTROL HEAD
OPERATOR INTERFACE (CONTROL HEAD - NOTE 2)
MAEPF-25078-A
P/O CONTROLLER
SECTION (NOTE 1)
Figure 1 . 900-MHz Radio Functional Block Diagram

8 Theory of Operation Revision B, 5/98
The controller generates the audio PA enable signal based on such
variablesasthelevelofthe received signal, the frequencychannel,and
the operating mode of the radio. When the audio PA enable signal is
generated, the audio power amplifier (PA) is activated and passes the
receiver audio signal to the loudspeaker.
The transmitter function of the radio produces either a 12-Watt or a
30-Wattradiofrequencyoutputsignal,dependingonthemodelof the
radio.The radio frequency output signal is frequencymodulated by an
audio signal from the microphone or from another source such as a
telephone keypad or handset.
The transmitter function of the radio consists of: the audio signal filter
integrated circuit (ASFIC) in the controller section; the synthesizer
section; and the transmitter power amplifier (PA) section. The ASFIC
develops a modulation signal by amplifying an audio signal from the
microphone, keypad, or handset. The synthesizer section generates a
radio frequency carrier signal upon which the transmitter portion of
the radio operates.The radio frequency carrier signal generated by the
synthesizer section is frequency modulated in the synthesizer section
by the modulation signal output from the ASFIC.
The frequency modulated output signal from the synthesizer section
is amplified to the required 12-Watt or 30-Watt power level by the
power amplifier (PA) section.The output of the PA section passes
through the antenna switch and is radiated by the vehicle antenna or
fixed-station antenna.
The controller section of the radio contains a microprocessor that
controls the radio in accordance with its built in programming as well
as commands input manually by the radio operator. The radio
operator inputs manual commands to the controller section using the
pushbuttons and other controls located on the control head. In
addition to its controlling functions, the controller section provides
audio amplification of the audio output signal in the receiver
function. It also contains squelch detect circuitry based on a buffered
discriminator signal from the Zero Intermediate Frequency Integrated
Circuit (ZIF IC).
The operator interface function of the radio consists of: a microphone
or the microphone portion of a telephone handset; a telephone
keypad if used; the pushbuttons and other controls on the control
head; and the digital and graphics displays on the control head. The
pushbuttons and other controls on the control head provide digital
commandstothecontrollersection, and in some instances, hardwired
commands to controlled circuits. The digital and graphics displays
receive display data from the controller section. The control head
contains its own microprocessor, which communicates with the
controller section of the radio via an SB9600 serial digital data bus.
The DC power control and regulation function regulates and
distributes to the various sections of the radio, DC power from the
vehicle battery or fixed station power supply.

Revision B, 5/98 Theory of Operation 9
Receiver
Detailed Functional
Description
The portion of the receiver function that is not part of the controller
section of the radio is composed of three sections: receiver front end;
receiver If, and receiver back end.
Receiver Front End
(All Kits)
The following discussion is based on the schematic diagram for the
receiver front end section on page 37. The received RF signal (RX_IN)
from the antenna switch in the PA section of the radio enters the first
bandpass filter FL6250. The first bandpass filter has three poles, a 938-
MHz center frequency, a 6-MHz wide passband, and a 45-dB ultimate
rejection for frequencies outside the passband.
After the first bandpass filter, the received RF signal goes to a pair of
hot carrier limiting diodes (CR6250). The hot carrier diodes limit
strong signals to prevent them from over driving and damaging RF
preamplifier Q6271.
The main purpose of RF preamplifier Q6271 is to set the noise figure
of the receiver. Q6271 is actively biased through Q6272. During
transmit, the RF preamplifier is shut off by the K9.1 line via switch
Q6250 and bias transistor Q6272. After the signal leaves the RF
preamplifier, it enters second bandpass filter FL6251, which is
identical to FL6250.
When the RF signal leaves the second bandpass filter, it goes into
mixer U6251. The mixer is the double balanced active Gallium
Arsenide type. The RF signal is applied to the mixer through balun
transformer T6251. The first injection local oscillator is applied to the
mixer via balun transformer T6252 and is 73.35 MHz below the RF
signal frequency. The bias for the mixer is set by resistors R6285,
R6286, and R6287. The IF output signal from the mixer, which is at a
frequency of 73.35 MHz, is fed to the receiver IF section as IF_OUT
through transformer T6253.
Receiver Intermediate
Frequency (IF)
(Kits FLF5591A, B, C;
FLF5592A, B, C;
HUF1190A; HUF1191A)
The following discussion is based on the schematic diagram for the
receiver IF section on page 39.
The IF_OUT signal from the receiver front end section enters the
receiver IF section as the IF_IN signal. The first circuit in the receiver
IF section is a resistive pad (R6376, R6377, R6378, R6392), which
stabilizes the impedance presented to the output of the mixer in the
receiverfrontendsection.Italsostabilizestheimpedancepresentedto
the input of the first 73.35-MHz crystal filter, Y6376.
From the resistive pad, the signal passes through to the first 73.35-
MHz crystal filter, Y6376 whose surrounding components match it to
50-ohms and to the input of IF amplifier Q6388. A matching network,
which follows Q6388, matches the IF amplifier output impedance to
the input impedance of the second 73.35-MHz crystal filter, Y6377.
Both crystal filters have two-poles and have a bandwidth of 13kHz to
accommodate the bandwidth requirements for digital data. Matching
elements, which follow the second crystal filter, match the output of
the second crystal filter to the input of the receiver back end section.
The signal out of the receiver IF section (IF_V_OUT) passes through

10 Theory of Operation Revision B, 5/98
connector J6400 and jumper plug J6401 to the input of the receiver
back end section.
Receiver IF
(Kits FLF5604A,
FUF5752A, FLF5952A,
FLF5606A)
The following discussion is based on the schematic diagram for the
receiver IF section on page 41.
The IF output signal (IF_OUT) from the receiver front end section
enters the receiver IF section as IF_IN and passes into three automatic
gain control (AGC)/attenuator stages. The first AGC/attenuator stage
is formed by diodes CR6251 and CR6253 and the associated circuitry,
thesecond stage by CR6252, CR6254, and theassociated circuitry, and
the third stage by CR6255, CR6256 and the associated circuitry.
The three attenuators are controlled by the radio signal strength
indicator (RSSI) signal, from the zero intermediate frequency
integrated circuit (ZIF IC), in the receiver back end section, via a DC
shiftandintegratorcircuitformed by two of the operational amplifiers
in U6202. For the lowest level IF_IN signals, the attenuator stages
attenuate minimally. For the highest level signals, they attenuate
approximately 25dB per stage. The attenuator stages are designed for
minimum VSWR, which means that for any level of operation they
present a matched port to the surrounding circuitry.
The principle of operation for the attenuator stages, taking the first
stage as an example, is the followings: The main components in the
attenuator are the two diodes, CR6251 and CR6253. The attenuator is
biased by two lines, a constant +5V line, connected to the anode of
diode CR6253, and a control line driven by the RSSI signal via the
operational amplifiers in U6202.
For a high signal level, the attenuation is at maximum value because
the control line is at 0V, which causes CR6251 to be zero biased while
CR6253 is maximum biased. This makes the IF signal flow to ground
throughR6366,C6367(whichactsas a DC block), CR6253,andC6372
(which is also a DC block). The input signal sees a 50-ohm match,
which is roughly the sum of the impedances formed by the above
mentioned components.
For low signal levels, the attenuation is at minimum value because the
control line is at +5V and CR6251 is maximum biased while CR6253
is zero biased. The DC return for the control line is through R6368 and
R6370. The large values (470K) of these two resistors makes them also
function as RF blocks.
The control line is driven by the RSSI signal line from the ZIF IC in the
receiver back end section. The RSSI signal is amplified and DC shifted
through one of the operational amplifiers of U6202 and the associated
circuitry formed by resistors R6342 through R6345. This then passes
though the inverting integrator formed by another operational
amplifier of U6202 and C6362, R6358, R6359, R6360 and R6361. The
result is that for the lowest RSSI voltage, the control line is +5V and for
the highest RSSI voltage, the control line is 0V.
The inherent insertion loss of these attenuators ensures that a good
match is presented to the output of the front-end mixer.

Revision B, 5/98 Theory of Operation 11
The third attenuator stage formed by CR6255 and CR6256 is optional
and is bypassed by R6357 with C6366 and R6350 not being placed.
Receiver Back End
(All Kits)
The following discussion is based on the schematic diagram for the
receiver back end section: page 43 for kits FLF5591A, B, C and
FLF5592A, B, C; page 45 for kits FLF5604A, FUF5752A, FLF5952A, and
FLF5606A; and page 47 for kits HUF1190A and HUF1191A. From the
output of the receiver IF section, the IF signal (IF_IN) enters IF
amplifier Q6203. A pair of hot carrier limiter diodes (CR6203) at the
base of the IF amplifier protect U6201, the Zero Intermediate
Frequency Integrated Circuit (ZIF IC), from strong signal overloading.
With kits FLF5591A, B, C and FLF5592A, B, C, the output of IF
amplifier Q6203 is fed to a shunt pin diode attenuator, CR6203. The
attenuation provided by the pin diode attenuator is a function of the
signal level detected by the internal automatic gain control (AGC)
circuit in the ZIF IC. As the RF level increases, the attenuation
increases. This ensures that the ZIF IC, whose dynamic range is much
less than that of the radio, is not over driven by strong signals, causing
distortion in the detected signal.
With kits FLF5604A, FUF5752A, FLF5952A, and FLF5606A, this
attenuation function is performed by the attenuator stages in the
receiver IF section and this ACG mechanism in the receiver back end
section is bypassed. To do this, shorting resistor R6224 is mounted
bypassing CR6203, which is not mounted, an additional shorting
resistor is placed on the pads of L6208 instead of the 1 microHenry
inductor, and CR6204 is not placed.
At the output of Q6203, there is a notch filter, for the third harmonic
of 73.35 MHz, made up of components C6249 and inductor L6207.
Transistor Q6201 and varactor diode CR6201 form the second local
oscillator (LO). The LO operates as a voltage controlled oscillator
(VCO), which is controlled by the ZIF IC.
The ZIF IC is a down converter, a filter, a limiter, and an FM
demodulator. The IF signal going into the ZIF IC at 73. 35MHz is down
converted, filtered, limited, and demodulated. Demodulated audio
comes out of the ZIF IC from pin 28 and is fed to the ASFIC audio
signal filtering IC, which is part of the controller section of the radio.
In addition to the audio output signal, the receiver section provides a
squelch signal output, which also is processed and used by the
controller section of the radio to mute the receiver output during
periods of no signal reception.
Refer to the discussion under the title Receive Audio Circuits , which is
located in the Controller Section Theory of Operation portion in Volume
1 of this service manual.

12 Theory of Operation Revision B, 5/98
Transmitter
Detailed Functional
Description
The transmitter function of the radio is distributed between the
controller, the synthesizer, and the transmitter power amplifier (PA)
sections. This is shown on the overall functional block diagram for the
radio, Figure 1. The portion of the transmitter function physically
located in the controller section is described in the Controller Section
Theory of Operation located in Volume 1 of this service manual. That
portion includes the audio circuits that filter, amplify, and otherwise
process the audio signal from the microphone and/or telephone
handset. The portion of the transmitter function located in the
synthesizer section of the radio is described in the Synthesizer Detailed
Functional Description in this volume of the service manual. The
synthesizer section of the transmitter receives the amplified and
processed audio signal from the controller section and produces a
frequency-modulated radio frequency carrier (injection) signal, which
is input to the transmitter power amplifier (PA) section.
The remaining part of the transmitter function of the radio is located
in the PA section. The following discussion covers the part of the
transmitter function that is physically located in the PA section.
There are two different configurations of the PA section; one for the
12-Watt radio, and the other for the 30-Watt radio.
12-Watt Power Amplifier
(Kits FLF5591A, B, C;
FLF5604A, FLF5952A;
HUF1190A)
The following discussion is based on the schematic diagram for the 12-
Watt power amplifier (PA), on page 49 for kits FLF5591A, B, C,
FLF5604A, and HUF1190A and on page 51 for kit FLF5952A.
The power amplifier (PA) is a radio frequency (rf) power amplifier,
which amplifies the output from the injection string (TX_INJ) to an RF
output power level of 12 Watts. It consists of a driver stage Q6501,
followed by a power amplifier module U6501.
In kits FLF5591A, B, C and FLF5604A, the second and third stages of
U6501 operate directly from the A+ supply voltage received from
connector J6502 via current sense resistor R6520. To protect the input
stage from voltage transients on the A+ line, the first stage of U6501 is
operated from the keyed K9.1 voltage, which is provided by the
controller section of the radio.
In kit FLF5952A, two DC supply inputs for U6501 (+DCISUP and
+DCISUPP) are obtained directly from the A+ line via R6520. The
transmit enable input (+DCBIAS) is obtained from the A+ line via
R6520 and switch U6502, which is controlled by the keyed K9.1
voltage.
The rf drive, which is routed into transistor Q6501, is controlled from
Q6506 via the PA control line. A rising control voltage on the PA
control line causes a rising collector voltage on Q6501. This causes
more power to be delivered into the next stage. Conversely, a
decreasing control line voltage decreases the power delivered into the
next stage. By controlling the drive power to U6501 and the following
stages in the power amplifier lineup, automatic level control (ALC) is
accomplished, which regulates the output power of the transmitter.