Midland Syn-Tech III P25 User manual

Service Manual
Revised 4.24.2009
Part Number 680-100-2020
Complete Service Information
for
STP-105B VHF Portable
and
STP-404(A)(B) UHF Portable
SYN-TECH III P2
5
P
O
RTABLE RADI
O

SYN-TECH III P25 PORTABLE RADIO
SERVICE MANUAL
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OUR THANKS TO YOU
PREFACE
Thank you for purchasing the Midland Syn-Tech III P25 Portable Radio. Properly used, this product will
provide you many years of reliable service.
To get the most out of your purchase, be sure to carefully read this manual and keep it on hand for later
reference when needed.
Before servicing your radio, please read this entire manual.
CUSTOMER ASSISTANCE
If you require further assistance, please contact your local Midland dealer.
FOR WARRANTY, PRODUCT SERVICE AND ACCESSORY INFORMATION
Please contact your local Midland dealer or distributor.
Do not attempt to service any internal parts yourself.
This radio should be opened by authorized personnel only.
Otherwise, the warranty VOIDS.
Your radio is packed and labeled according to commercial packaging standards.
SYN-Tech III P25 Portable Radio is designed and manufactured for Midland Radio Corporation.
PATENT AND COPYRIGHT STATEMENTS
The AMBE+2™ voice coding Technology embodied in this product is protected by intellectual
property rights including patent rights, copyrights and trade secrets of Digital Voice Systems,
Inc. This voice coding Technology is licensed solely for use within this Communications
Equipment. The user of this Technology is explicitly prohibited from attempting to extract,
remove, decompile, reverse engineer of disassemble the Object Code, or in any other way
convert the Object Code into a human readable form. U.S. Patents Nos. #5,870,405,
#5,826,222, #5,754,974, #5,701,390, #5,715,365, #5,649.050, #5,630,011, #5,581,656,
#5,517,511, #5,491,772, #5,247,579, #5,226,084, and #5,195,166

SYN-TECH III P25 PORTABLE RADIO
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IMPORTANT SAFETY INFORMATION
GENERAL PRECAUTIONS
Use only MIDLAND authorized accessories. (Antennas, batteries, chargers, belt clips,
speaker/microphone sets, tactical headsets etc.).
Using unauthorized accessories may result in personal injury or cause damage to the
radio.
Charger is for indoor use only. Avoid direct sunlight and extreme heat sources. Use in a
dry cool place at max 40ºC.
CAUTION
Changes or modifications to radio may void its compliance with government laws/rules
and make it illegal to use.
Avoid using the radio at temperatures below -22ºF or above 140ºF.
Avoid storing the radio at temperatures below -40ºF or above 185ºF.
The charger is to be used for charging purposes only. It is not to be used during transmit.
Red light on the front of charger will change to green indicating the radio is fully charged.
For the initial charge, leave your radio in the charger for 4 to 6 hours.
WARNINGS
Your MIDLAND SYN-Tech III P25 Portable Radio generates electromagnetic RF energy
when transmitting. Ensure that you, and those around you, are not exposed to excessive
amounts of that energy (beyond recommended allowable limits for occupational use):
ALWAYS hold the radio, especially the antenna, at least 5 cm (2 inches) away from
yourself when transmitting.
WARNINGS ABOUT BATTERY
Do not place battery into fire.
Damaged battery may release dangerous chemical gasses. DO NOT breathe the fumes.
Misuse of battery may cause fire and/or explosion.
Do not disassemble battery pack. Battery cells contain electrolyte liquid which is damaging
to skin and clothes.
Do not short circuit + and – poles of battery pack. Short circuit between poles with metal
object may cause permanent damage to battery and may cause a fire.
Battery packs that have completed their life cycle must be disposed of properly.
If explosive gasses exist, do not remove or change battery. Movement of battery contacts
may cause spark, resulting in an explosion.

SYN-TECH III P25 PORTABLE RADIO
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NOTES
.

SYN-TECH III P25 PORTABLE RADIO
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TABLE OF CONTENTS
1DEFINITIONS, ABBREVIATIONS AND ACRONYMS ............................................................................1-1
1.1 DEFINITIONS ................................................................................................................................... 1-1
1.2 ABBREVIATIONS AND ACRONYMS .............................................................................................. 1-1
2INTRODUCTION.......................................................................................................................................2-1
2.1 GENERAL FEATURES .................................................................................................................... 2-1
2.2 TECHNICAL SPECIFICATIONS ...................................................................................................... 2-2
3DESCRIPTION OF THE RADIO...............................................................................................................3-1
3.1 CONNECTION DIAGRAM................................................................................................................ 3-1
3.2 Operating Principles ......................................................................................................................... 3-2
3.2.1 RF and Control PCB..............................................................................................................3-2
3.2.2 Display and Keypad PCB ...................................................................................................... 3-4
3.2.3 DSP PCB............................................................................................................................... 3-4
4ADJUSTMENT..........................................................................................................................................4-1
4.1 DEFINITIONS AND ABBREVIATIONS ............................................................................................ 4-1
4.2 ADJUSTMENT CONDITIONS.......................................................................................................... 4-1
4.3 ADJUSTMENT SETUP..................................................................................................................... 4-1
4.4 ADJUSTMENT PROCEDURES ....................................................................................................... 4-3
4.4.1 RF Output Power Adjustment................................................................................................ 4-3
4.4.2 Analog Frequency Adjustment 25 kHz.................................................................................. 4-3
4.4.3 Digital Frequency Adjustment ............................................................................................... 4-3
4.4.4 Modulation Flatness Adjustment ........................................................................................... 4-3
4.4.5 Modulation Limiting Adjustment ............................................................................................ 4-4
4.4.6 FM Deviation Adjustment ...................................................................................................... 4-4
4.4.7 C4FM Deviation Adjustment.................................................................................................. 4-4
4.4.8 Squelch Adjustment............................................................................................................... 4-4
4.4.9 RSSI Adjustment ................................................................................................................... 4-5
4.4.10 C4FM Receive Level Adjustment .......................................................................................... 4-5
5TROUBLESHOOTING .............................................................................................................................5-1
6ILLUSTRATED PART LISTS...................................................................................................................6-1
6.1 SYN-TECH III P25 PORTABLE MAIN ASSEMBLIES...................................................................... 6-2
6.2 SYN-TECH III P25 PORTABLE RADIO PCB ASSEMBLIES........................................................... 6-4
6.3 SYN-TECH III P25 PORTABLE RADIO REAR PANEL ASSEMBLY............................................... 6-6
6.4 SYN-TECH III P25 PORTABLE RADIO FRONT PANEL ASSEMBLY ............................................ 6-8
6.5 SYN-TECH III P25 PORTABLE RADIO DISPLAY AND KEYPAD PCB ASSEMBLY....................6-10
6.6 SYN-TECH III P25 PORTABLE RADIO DSP PCB ASSEMBLY.................................................... 6-14
6.7 SYN-TECH III P25 PORTABLE RADIO VHF RF AND CONTROL PCB ASSEMBLY................... 6-17
6.8 SYN-TECH III P25 PORTABLE RADIO UHF RF AND CONTROL PCB ASSEMBLY...................6-24
7DISASSEMBLY AND ASSEMBLY..........................................................................................................7-1
7.1 REQUIRED EQUIPMENT ................................................................................................................ 7-1
7.2 USAGE ............................................................................................................................................. 7-2
7.3 DISASSEMBLING THE RADIO........................................................................................................7-2
7.4 DISASSEMBLING THE PCB ASSEMBLY ....................................................................................... 7-5
8SCHEMATIC DIAGRAMS........................................................................................................................8-1
8.1 RADIO CONNECTOR PINOUT........................................................................................................ 8-2
8.1.1 Side Control........................................................................................................................... 8-2
8.1.2 Audio Control......................................................................................................................... 8-2
8.1.3 External Accessory................................................................................................................ 8-2
8.2 VHF RF SCHEMATIC 136-174 MHz ................................................................................................ 8-3
8.3 UHF RF SCHEMATIC 380-470 MHz................................................................................................ 8-4

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8.4 UHF RF SCHEMATIC 450-512 MHz................................................................................................ 8-5
8.5 CONTROL SCHEMATIC .................................................................................................................. 8-6
8.6 DSP SCHEMATIC ............................................................................................................................ 8-7
8.7 LCD AND KEYPAD SCHEMATIC .................................................................................................... 8-8
FIGURES
Figure 3-1: Midland Syn-Tech III P25 Portable Radio Connection Diagram .................................................. 3-1
Figure 4-1: Adjustment Setup ......................................................................................................................... 4-2
Figure 6-1: Main Assemblies Location Diagram ............................................................................................. 6-2
Figure 6-2: PCB Assemblies Location Diagram.............................................................................................. 6-4
Figure 6-3: Rear Panel Assembly Location Diagram...................................................................................... 6-6
Figure 6-4: Front Panel Assembly Location Diagram ..................................................................................... 6-8
Figure 6-5: Display and Keypad PCB Location Diagram -1..........................................................................6-10
Figure 6-6: Display and Keypad PCB Location Diagram -2..........................................................................6-11
Figure 6-7: DSP PCB Location Diagram -1 .................................................................................................. 6-14
Figure 6-8: DSP PCB Location Diagram -2 .................................................................................................. 6-15
Figure 6-9: VHF RF and Control PCB Location Diagram -1 ......................................................................... 6-17
Figure 6-10: VHF RF and Control PCB Location Diagram -2 ....................................................................... 6-18
Figure 6-11: UHF RF and Control PCB Location Diagram -1....................................................................... 6-24
Figure 6-12: UHF RF and Control PCB Location Diagram -2....................................................................... 6-25
TABLES
Table 2-1: Syn-Tech III P25 Portable Radio General Specifications .............................................................. 2-2
Table 2-2: Batteries for Syn-Tech III P25 Portable Radios............................................................................. 2-2
Table 2-3: Syn-Tech III P25 Portable Radio Environmental Specifications.................................................... 2-2
Table 2-4: Syn-Tech III P25 Portable Radio Receiver Specifications ............................................................ 2-3
Table 2-5: Syn-Tech III P25 Portable Radio Transmitter Specifications ........................................................ 2-4
Table 3-1: KN1, RF and Control PCB to DSP PCB Signals ...........................................................................3-6
Table 3-2: KN2, RF and Control PCB to Display and Keypad PCB Signals .................................................. 3-7
Table 4-1: Spurious Signal Frequencies......................................................................................................... 4-1
Table 5-1: Syn-Tech III P25 Portable Radio Error Messages......................................................................... 5-1
Table 5-2: Syn-Tech III P25 Portable Radio Alert Messages ......................................................................... 5-2
Table 5-3: Syn-Tech III P25 Portable Radio ‘Problem-Solution’ Table........................................................... 5-3
Table 6-1: Main Assemblies Parts List............................................................................................................ 6-3
Table 6-2: PCB Assemblies Parts List ............................................................................................................ 6-5
Table 6-3: Rear Panel Assembly Parts List .................................................................................................... 6-7
Table 6-4: Front Panel Assembly Parts List.................................................................................................... 6-9
Table 6-5: Display and Keypad PCB Parts List ............................................................................................6-12
Table 6-6: DSP PCB Parts List .....................................................................................................................6-16
Table 6-7: VHF RF and Control PCB Assembly Parts List ...........................................................................6-19
Table 6-8: UHF RF and Control PCB Assembly Parts List...........................................................................6-26

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1 DEFINITIONS, ABBREVIATIONS AND ACRONYMS
1.1 DEFINITIONS
Channel :
The frequency or frequency pair which is used for transmission and/or
receiving of electrical or electromagnetic signals.
Channel Spacing : Distance between center frequencies of two neighboring channels.
Protocol :
Required rules sequence to be able to carry out a definite communication
function.
Site :
Location that contains one or more Repeater Radios, Assistant Units and
equipment groups that supply a determined coverage area. It has
connection to other Sites and/or Control Units.
Squelch :
TA radio circuit that mutes the loudspeaker when no valid transmitted signal
is detected.
1.2 ABBREVIATIONS AND ACRONYMS
A T:T Ampere
AES T:T Advanced Encryption Standard
APCO T:T The Association of Public-Safety Communications Officials
BER T:T Bit Error Rate
BPF T:T Band Pass Filter
C4FM T:T Continuous 4-Level Frequency Modulation
CD T:T Carrier Detect
CDCSS T:T Continuous Digital Coded Squelch System
CS T:T Chip Select
CTCSS T:T Continuous Tone Controlled Squelch System
dB T:T Decibel
dBm T:T Decibel Milliwatt
DC T:T Direct Current
DES T:T Data Encryption Standard
DSP T:T Digital Signal Processing
DSR T:T Data Set Ready
DTMF T:T Dual Tone Multi Frequency
DTR T:T Data Terminal Ready
EEPROM T:T Electrically Erasable Programmable Read Only Memory
EPROM T:TElectronically Programmable Read Only Memory
ESD T:T ElectroStatic Discharge

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FFSK T:T Fast Frequency Shift Keying
FM T:T Frequency Modulated
FPC T:T Flexible Printed Circuit
GPS T:T Global Positioning System
HPI T:T Host Port Interface
Hz T:T Hertz
IC T:T Integrated Circuit
IEC T:T International Electrotechnical Commission
IF T:T Intermediate Frequency
IMBE T:T Improved Multi-Band Excitation
kb/s T:T Kilobit per second
kg T:T Kilogram
LCD T:T Liquid Crystal Display
LNA T:T Low Noise Amplifier
LO T:T Local Oscillator
MCU T:T Microcontroller Unit
MHz T:T Mega Hertz
MIL-STD T:T Military Standards
mm T:T Millimeter
OFB T:T Output Feedback
PC T:T Personal Computer
PCB T:T Printed Circuit Board
ppm T:T Parts Per Million
RF T:T Radio Frequency
RSSI T:T Received Signal Strength Indicator
Rx T:T Receive
SINAD T:T SIgnal Noise And Distortion
SPI T:T Serial Peripheral Interface
TCXO T:T Temperature Controlled Crystal Oscillator
Tx T:T Transmit
UHF T:T Ulltra High Frequency
V T:T Volt
VCO T:T Voltage Controlled Oscillator

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VHC T:T Vehicular
VHF T:T Very High Frequency
VOGAD T:T Voice Operated Gain Adjusting Device
VSWR T:T Voltage Standing Wave Ratio
W T:T Watt
WACN T:TTT Wide Area Communication Network

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2 INTRODUCTION
2.1 GENERAL FEATURES
Midland Syn-Tech III P25 portable radios have the following features:
• 136-174 MHz VHF
• 380-470 MHz UHF(A)
• 450-512 MHz UHF(B)
• Mixed analog and digital mode operation
• Easy installation
• Low maintenance
• Tri-color LCD display
• Full keypad
• High quality audio
• User friendly interface
• Extensive user prompts, alerts and warnings
• Flexible accessory connections
• Microprocessor controlled
• DSP based audio
• Flash memory
• Synthesized frequency control
• Extensive use of surface mount technology
• PC controlled testing and alignment
• CTCSS/CDCSS sub-audible signaling
• 2-Tone / 5-Tone analog signaling
• Analog DTMF encoding
• Conforms with TIA/EIA-603-A standard in analog mode
• Conforms with APCO25 TIA/EIA-102-CAAB standard in digital mode
• Conforms with MIL-STD-810E standards

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2.2 TECHNICAL SPECIFICATIONS
Table 2-1: Syn-Tech III P25 Portable Radio General Specifications
Modulation 16K0F3E, 11K0F3E, 11K0F1D, 11K0F2D, 11K0F1E
Data Rate P25 : 9.6kb/s
Symbol Rate P25 : 4.8kb/s
Protocol Project 25-CAI : 4.4kb/s IMBE
Channel Capacity 255 zones / 999 channels
Operating Voltage Range 7.5VDC ±20% (6.0-9.0VDC)
St-by Current Drain (Backlight off) 25mA with power save
75mA without power save
RX Current Drain 240mA
TX Current Drain 1800mA
Display 64x128 pixel LCD
Keypad 18 back lit
Dimensions without battery (HxWxL) 6” x 2.375” x 1.375” (152 x 60 x 35mm)
Weight with antenna and battery 7.5oz (212.6g)
Table 2-2: Batteries for Syn-Tech III P25 Portable Radios
Battery Type Type
Number Dimensions (HxWxL) Weight Capacity Battery Life*
High Capacity
Li-Ion ACC-1800 4.45” x 2.065” x 0.63” (113 x 53 x 16 mm)
4.3oz
(135g) 1800mAh
5-5-90 Duty
≥18 h w/ PS
≥12 h w/o PS
Clamshell for
alkaline batteries 90-1015 10-10-80 Duty
12 hrs @ 2 W
Table 2-3: Syn-Tech III P25 Portable Radio Environmental Specifications
Operating Temperature Range -22°F / +140° (-30°C / +60°C)
Storage Temperature Range -40°F / +185° (-40°C / +85°C)
Humidity 95% @ 122°F (50°C)
ESD IEC 801- 2KV
Water and Dust Protection IP65, MIL-STD
* Measured in the digital mode per TIA 102.CAAA under nominal conditions at 5.0 W RF output power.

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Table 2-4: Syn-Tech III P25 Portable Radio Receiver Specifications
VHF UHF
Frequency Range 136-174MHz 380-470MHz
450-512MHz
Frequency Separation Full Band split
Channel Spacing 12.5 / 25 kHz
Frequency Step 2.5 / 3.125kHz
Rated Audio Output Power * 500mW / 8
Frequency Stability *
(-30°C / +60°C; 25°C ref) ±2.5ppm ±1.5ppm
Analog Sensitivity *
12 dB SINAD -119dBm -118dBm
Digital Sensitivity **
5% BER -119dBm -117dBm
1% BER -117dBm -116dBm
Adjacent Channel Rejection
Analog 25 kHz channel * 73dB 70dB
Analog 12.5 kHz channel * 63dB 60dB
Digital 12.5 kHz channel ** 63dB 60dB
Intermodulation Rejection * 73dB
Spurious Response Rejection* 73dB
Hum and Noise Ratio
Analog 25 kHz channel *
48dB 42dB
Analog 12.5 kHz channel * 42dB 36dB
Digital 12.5kHz channel ** 50dB 50dB
Audio Distortion * 3%
* Measured in the analog mode per EIA-603 under nominal conditions.
** Measured in the digital mode per TIA-102.CAAA under nominal conditions.

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Table 2-5: Syn-Tech III P25 Portable Radio Transmitter Specifications
VHF UHF
Frequency Range 136-174MHz 380-470MHz
450-512MHz
Frequency Separation Full Band split
Channel Spacing 12.5 / 25 kHz
Frequency Step 2.5 / 3.125kHz
Rated RF Output Power * 0.2–5 W 0.2–5 W
Frequency Stability *
(-30°C / +60°C; 25°C ref) ±2.5ppm ±1.5ppm
Modulation Limiting *
Analog 25 kHz channel
Analog 12.5 kHz channel
±5.0kHz
±2.5kHz
C4FM Modulation Fidelity **
RMS Error
C4FM Deviation
2.5%
1800 ±100Hz
Spurious Emissions *
(Conducted and Radiated) -70dBc
Audio Frequency Response *
(6dB/Octave Pre-emphasis
from 300 to 3000Hz)
+1, -3dB
Hum and Noise Ratio
Analog 25kHz channel *
Analog 12.5kHz channel *
52dB
46dB
46dB
40dB
Audio Distortion * 2%
* Measured in the analog mode per EIA-603 under nominal conditions.
** Measured in the digital mode per TIA-102.CAAA under nominal conditions.

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3 DESCRIPTION OF THE RADIO
3.1 CONNECTION DIAGRAM
Midland Syn-Tech III P25 Portable Radio Connection Diagram is given below.
Figure 3-1: Midland Syn-Tech III P25 Portable Radio Connection Diagram
ASSY FPCB HH PTT\SIDE KEYS, ASSY FPCB HH AUDIO POT\SEL KEYS and
ASSY FPCB HH EXT ACCESSORY are parts of the ASSY FRONT PANEL
STM Series P25 Portable MIDLAND (P/N: 5999-9037-2140).

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3.2 Operating Principles
3.2.1 RF and Control PCB
The RF and Control Board is designed to be used in Syn-Tech III P25 Portable Radio. It consists of
Receiver Circuits, Transmitter Circuits, Voltage Controlled Oscillator Circuits, Frequency Synthesizer
Circuits, Control Circuits and Audio Frequency Circuits. The board is supplied by 7.5 VDC voltage.
The RF and Control Board carries out receive and transmission functions at the VHF frequency band,
136-174 MHz, the UHF(A) frequency band, 380-470 MHz, or the UHF(B) frequency band, 450-512 MHz.
In receive mode the FM/C4FM modulated RF signal from antenna at selected channel frequency is
decoded. The base band signal is sent to the Keypad and Display Board as audio or data to be
monitored. In transmit mode the base band signal (audio or data) is transformed into an FM modulated
RF signal on selected channel frequency and transmitted to the antenna to be broadcast.
The stand-by mode is used to extend battery life by limiting current. Only the circuits necessary to detect
a signal are active. The circuits operate 5 ms active and 100 ms stand-by in analog mode and 5 ms
active and 25 ms stand-by in digital mode.
3.2.1.1 Receiver Circuits
Receiver circuits have a dual conversion super heterodyne structure. They consist of RF pre input
circuits, first mixer, bi-directional intermediate frequency duplexer, first amplifier of the first intermediate
frequency, 4 pole first intermediate frequency crystal filter, second amplifier of first intermediate
frequency, second mixer, 4 or 6 pole second intermediate frequency ceramic filter, second intermediate
frequency amplifier limiter and FM decoder circuits.
The RF signal from the antenna first passes through the pre input circuits. The RF signal passes through
a low pass harmonic filter, T/R switch and band pass filter or tuned notch filter. The UHF radio’s notch
filter frequency is tuned by the BPF_ADJUST voltage. This 1-4 volt swing tunes the notch from 290-380
MHz.
The RF signal is then amplified about 15 dB by the low noise pre-amplifier and then filtered by a tuned
band pass filter. The 1-4 Volt BPF_TUNE (BPF_ADJUST) adjusts the filter’s center frequency to the
channel frequency, Fchan.
The 45 MHz first IF frequency is obtained by mixing the RF signal with the first local oscillator signal,
Fchan-45 MHz. The first IF frequency is filtered amplified and then filtered by the 4 pole crystal filter. The
crystal filter has a 3 dB bandwidth of ±6 KHz. The output of the crystal filter is then amplified by another
first IF amplifier and input to the second mixer within the demodulator IC.
The 450 KHz second IF frequency is obtained by mixing the signal with the 44.550 MHz second local
oscillator signal. The 44.550 MHz second local oscillator signal is obtained as the third harmonic of the
14.85 MHz TCXO. The 450 KHz second IF frequency is filtered by the wide (4 pole, ±7.5 KHz 6 dB
bandwidth) or narrow (6 pole, ±2 KHz 6 dB bandwidth) ceramic filters then sent into the limiter. The
amplifier clipper signal is passed to the fm decoder and the audio + noise signal is output from the
demodulator IC and is sent to an 8 KHz low pass filter to obtain the RX_AUDIO signal and to the noise
filter to get the NOISE_DET_OUT signal.
The NOISE_DET_OUT signal is compared to the SQUELCH_POWER_TUNE (S_G_ADJUST) voltage to
obtain the SQUELCH signal which is sent to the MCU. Additionally, the RSSI signal from the demodulator
IC is sent to the MCU.
3.2.1.2 Transmitter Circuits
The transmitter circuit’s primary function is to amplify the signal from the voltage controlled oscillator, and
transmit it to the antenna between 0.2 W - 5 W output power ranges. The transmitter circuits consist of
driver amplifier, power amplifier, receiver-transmitter switch, harmonic filter and power control units.
The 17-18 dBm level signal from the transmitter VCO is amplified by the driver amplifier, TR502 , then by
the power amplifier , TR501. The signal from the power amplifier is sent to the antenna through the

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receiver-transmitter switch and the 7 pole harmonic filter. Harmonics are suppressed more than 45 dB by
the filter.
The power control circuits monitor the current drawn by the driver and power amplifier by the voltage drop
across R503 (R506). This voltage is compared to the SQUELCH_POWER_TUNE (S_G_ADJUST) and
the difference signal is applied to the transistors’ gates to regulate the output power.
3.2.1.3 VCO Circuits
The Voltage Controlled Oscillator (VCO) circuits are designed separately as a receiver VCO (RX VCO)
and a transmitter VCO (TX VCO). The TX VCO circuit operates at the channel frequency, 136-174 MHz
(380-470 MHz). Since the first IF is selected as 45 MHz, the RX VCO circuit operates at Fchan + 45 MHz,
181-219 MHz (Fchan – 45 MHz, 335-425 MHz).
The Colpits oscillators are supplied approximately 3.5V which is filtered from the REG5V source. The
3.5V is switched on by the RX_ON or TX_5V (sourced from TX_ON) signal such that only one oscillator is
running.
When RX_ON switches to 3V the RX VCO circuits begin to operate. The oscillating signal is amplified by
TR301 and low pass filtered to suppress unwanted signals. The signal is applied to the LO terminal of the
first mixer and the R_VCO signal is also fed back to the synthesizer IC. The synthesizer IC controls the
RX VCO frequency by changing RX_VCO_TUNE (CONTROL) until the desired frequency is achieved,
Fchan + 45 MHz (Fchan - 45 MHz).
When TX_ON switches to 3V the TX VCO circuits begin to operate. The oscillating signal is amplified by
TD402 and TD401. The signal is now the proper amplitude and is applied to the amplifier circuits. The
T_VCO signal is also fed back to the synthesizer IC. The synthesizer IC controls the TX VCO by changing
TX_VCO_TUNE (CONTROL) until the desired frequency is achieved, Fchan.
3.2.1.4 Synthesizer Circuits
The synthesizer circuits are composed of the Temperature Controlled Crystal Oscillator (TCXO), dual PLL
synthesizer integrated circuit, loop filter, 5V and 3V voltage regulators. The frequency synthesizer
includes a phase detector, a current mode charge pump, as well as a programmable reference divider
and a feedback dual modulus frequency divider.
The VCO frequency is established by dividing the crystal reference signal down via the reference divider
to obtain a frequency that sets the comparison frequency to 2.5 kHz or 3.125 kHz depending on whether
the VCO frequency is a multiple of 2.5 kHz or 3.125 kHz. This reference signal is then presented to the
input of a phase/frequency detector and compared with the divided VCO signal, which was obtained by
dividing the VCO frequency down by way of the feedback counter.
The phase/frequency detector measures the phase error between the reference signal and the divided
VCO signal and outputs control signals that are directly proportional to the phase error. The charge pump
then pumps charge into or out of the loop filter based on the magnitude and direction of the phase error.
The loop filter converts the charge into a stable control voltage for VCO. The phase/frequency detector’s
function is to adjust the voltage presented to the VCO until the feedback signal’s frequency and phase
match that of the reference signal. When this “phase-locked” condition exists, the VCO frequency will be
N times that of the comparison frequency, where N is the feedback divider ratio.
The loop filter is optimized for fast locking low VCO noise, such that typical lock times are 10ms and 20ms
for receiver and transmitter synthesizers, respectively, at full range frequency jumps.
A two-point modulation technique is used to obtain a flat modulation response (±0.2dB amplitude ripple at
0-3kHz AF range). The TX_AUDIO_1 and TX_AUDIO_2 signals, which are applied to TXVCO and TCXO
simultaneously, are compensated by means of digital potentiometers to maintain the flat modulation
response across the RF range.
The TCXO provides the 14.850 MHz reference frequency used by the synthesizer and also the third
harmonic 44.550 MHz second LO frequency used by the demodulator.

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3.2.1.5 Control Circuits
The control circuits contain the M16C/64 series M62724 microprocessor. The microprocessor has a 384K
byte flash memory. The microprocessor uses 12.288 MHz crystal as clock. It divides this frequency by
two and uses 6.144 MHz as an internal clock. It uses 8 bit data bus structure for external memory access.
There is a 20K byte internal RAM in the microprocessor. A 128K byte external RAM is used as main
RAM. It can be upgraded to 256K byte if it is required. 4M byte EEPROM (Data Flash) is used.
3.2.1.6 Audio Circuits
The audio circuits are composed of mainly the CMX881 integrated circuit. This integrated circuit is a DSP
based mixed signal audio processing circuit. This circuit also processes the CTCSS, DTMF and FFSK
signals. It can run CTCSS and SelCall decode processes synchronously. It requires an 18.432MHz clock
signal. A 6.144MHz signal is generated from the microprocessor. Its 3rd Harmonic is received via filter to
get 18.432MHz clock signal. The CMX881 is a half-duplex integrated circuit, so it can not perform receive
and transmit functions simultaneously. Because the radio is also half-duplex this substructure is sufficient.
The RX_AUDIO signal from the receiver circuits is filtered and de-emphasized within the CMX881. The
output of the CMX881 is the AUDIO signal which is sent to volume control and on to the audio amplifier.
The MIC_AUDIO signal from the microphone element is pre-emphasized within the CMX881. The CM881
also processes the mic audio through the VOGAD circuit, and then the limiter circuit. The mic audio is
sent to the modulator as the TX_AUDIO1 and TX_AUDIO2 signals. The modulation levels and flatness
are adjusted by the tuned amplifiers between the output of the CMX881 and the TX_AUDIO1 and
TX_AUDIO2 signals.
3.2.2 Display and Keypad PCB
The display and keypad board is the user interface for SYN-Tech III P25 Portable Radio. The radio is
controlled by the On/Off-volume knob, channel switch and keypad, which are connected to the board by a
flexible connection. Data and warnings are shown by LEDs and the LCD Display. The radio's connection
to external equipment is achieved via the option connector which is connected to the board by a flexible
connection. In receive mode, the processed audio signal coming from the RF and Control board is
amplified and sent to the speaker. In transmit mode, the audio signal coming from the microphone is
amplified and routed to the RF and Control Board. The RF and Control Board is connected to the Display
and Keypad board by KN2.
3.2.3 DSP PCB
The digital board circuits are controlled by the DSP, TD1. There are two A/D-D/A (Analog/Digital–
Digital/Analog) converter integrated circuits on board. While analog to digital or digital to analog
conversions of audio signals are performed by one of these integrated circuits, analog to digital or digital
to analog conversions of digital modulation signals are performed by the other one. Supply circuits and
circuits that generate a clock signal are also located on the board.
The interface with the microcontroller is through the HPI, which is a special parallel port of the DSP. The
DSP has three synchronous serial ports. The DSP communicates with the baseband Modem A/D–D/A
converter through first serial port, and with the audio A/D –D/A converter through the second serial port.
In the following sections, these interfaces will be explained.
The DSP multiplies the 12.288MHz clock signal by three with the on-chip PLL, so the DSP clock rate
becomes 36.864MHz. For the purpose of power saving, the DSP switches to the stand-by mode while not
operating. The wake up interrupt is sent by the MCU.
3.2.3.1 UDSP–MCU Interface
The DSP is connected to the MCU by connector, KN1 and runs under the control of the MCU. The DSP–
MCU interface is realized through HPI-8 8-bit parallel interface of C54xDSP family. Both the DSP and
MCU can access the RAM area on DSP by HPI-8 interface. There are 8-bit bi-directional data bus and
control signals on interface. The data length used in interface is 16-bit, access is granted at two phases
from 8-bit port based on A0 signal indicating first or second byte. HPI-8 combines the two bytes and then
places it to DSP RAM as 16-bit.

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The MCU communicates with DSP by means of the HPI-8 address and data registers. The HPI-8 data
register in the DSP, includes bits controlling communication protocol. The HPI-8 communication
substructure does not run when DSP is in reset mode. Unless the DSP clock is activated, it remains in the
reset mode. The HPI-8 starts to operate when DSP exits reset mode. The HPI-8 accesses of MCU are
synchronous with the DSP clock signal. If the DSP and MCU attempt to access the same address, access
by the MCU has priority, and the DSP waits for one clock cycle.
Data communication on HPI-8 interface is made through 8-bit data bus (HD0-7). A1 and A2 control
signals select which register of HPI-8 will be accessed. Since the DSP has 16-bit structure, all HPI-8
accesses should be in two bytes. The MCU indicates whether it transfers first or second byte with the A0
signal.
The DSP-MCU communication has two main functions; to load (boot) the DSP when turned on and to
provide messaging during running. These functions are explained below.
In order to run a program on DSP, the program must be loaded to the DSP’s RAM. This process is called
booting the DSP. The “bootloader” program is located in DSP ROM. After reset the program transfers the
DSP code, from a source other than itself, to program memory of the DSP. The DSP boot process in the
radio is made through the HPI.
When the DSP sends a message, it writes the message code, message length and message content
onto “HPI_BUFFER” area and interrupts MCU via DSP_MC-IRQ line. The MCU reads the message from
the address specified when it receives the “interrupt” from the DSP_MC_IRQ output of the DSP.
3.2.3.2 UDSP – Baseband Modem A/D – D/A Converter Circuits
The C4FM signal used in digital modulation is generated by IC2. This integrated circuit is an A/D–D/A
converter using sigma–delta modulation method. Operating clock frequency is 12.288MHz.
Communication with DSP is made through the first synchronous serial port. The synchronous serial port
clock frequency is 6.144MHz. The required clock signal is genereated by IC2.
Digital data, which is coming from the DSP consisting of 16 bit data sampled at 48kHz, is converted into
analog in transmit mode. So, the C4FM baseband signal is obtained. Bit rate is 9600 bps and 10 times
over-sampling is used.
In receive mode, the baseband signal coming from RF and Control board is transferred to IC2 through J1
and digitally sampled at 48kHz with 16 bit resolution by IC2 is sent to the DSP through the serial port.
When the DSP is in idle mode, IC2 is kept at reset to consume less power. It is taken out of reset mode
through programming by means of the synchronous serial port for receive/transmit mode.
IC2 is operating as A/D converter (receive mode) or D/A converter (transmit mode) in radio units.
3.2.3.3 UDSP – Audio A/D – D/A Converter Circuits
The DSP communicates with audio band A/D–D/A Converter IC3 through a second serial port. IC3
synchronous serial port frequency is 2.048MHz and it is obtained by dividing 12.288MHz operating clock
signal by six with internal divider within IC3. Sampling frequency is 8kHz, resolution is 16 bit and linear
quantization is used.
IC3 samples the audio signal coming from MIC_BUFFER_AUDIO line in control board, in transmit mode
and sends the audio data to the DSP for digital processing. In receive mode, it sends the processed audio
data, which is coming from the DSP to control board through DIG_RX_AUDIO line by converting them
into analog signals. When not required, IC3 is left at reset mode to consume less power.
In these radios, IC3 is operated in receive and transmit modes.
3.2.3.4 UPower Circuits (IC4, IC5, IC6)
Step down converter, IC5, is adjusted so as to obtain the 3V3 DC voltage from DC power input coming at
4.5–24V interval which changes for different type of radios. The 3V3 signal is input to IC4 and IC6 linear
regulator integrated circuits. The 2.5V which IC2 and IC3 A/D–D/A converter integrated circuits require, is
obtained from IC4. The 1.5V core voltage of the DSP, is obtained from IC6.

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Table 3-1: KN1, RF and Control PCB to DSP PCB Signals
POSITION DEFINITION FUNCTION
KN1-1 SSP_CE_WR Microprocessor WRITE signal
KN1-2 BAT7V5 Unswitched, direct battery voltage
KN1-3 DSP_CS Select microprocessor’s DSP data
KN1-4 SW7V5 Switched battery voltage
KN1-5 RD Microprocessor RD signal
KN1-6 DSP_RESET RESET signal from microprocessor to digital board
KN1-7 CIK One bite communication signal that goes to CIK module
KN1-8 DSP_MC_IRQ Interrupt data that comes to microprocessor from digital board
KN1-9 RDY Microprocessor RDY signal
KN1-10 12.288MHz 12.288MHz clock signal
KN1-11 GND Ground
KN1-12 DIG_TX_AUDIO Audio signal that will be transmitted after coded
KN1-13 SENSE Sense data
KN1-14 SK_RX_AUDIO Decoded audio signal
KN1-15 D1 Microprocessor parallel data signal
KN1-16 EMERGENCY Emergency call signal
KN1-17 A1 Microprocessor address signal
KN1-18 CLEAR Clear signal data received from keypad
KN1-19 A2 Microprocessor address signal
KN1-20 D2 Microprocessor parallel data signal
KN1-21 A3 Microprocessor address signal
KN1-22 D3 Microprocessor parallel data signal
KN1-23 A0 Microprocessor address signal
KN1-24 D7 Microprocessor parallel data signal
KN1-25 BB_MODEM_RX Base band signal received from receiver
KN1-26 D6 Microprocessor parallel data signal
KN1-27 D0 Microprocessor parallel data signal
KN1-28 D5 Microprocessor parallel data signal
KN1-29 BB_MODEM_TX Base band signal that goes to transmitter
KN1-30 D4 Microprocessor parallel data signal