DX Radio Systems 9000V5 Service Manual

SRM 9000 Series

FM VHF/UHF Mobile Radio Transceiver

SERVICE MANUAL

TNM-M-E-0001

October 2000

Draft D

abcde

DRAFT D

Revision History

Revision Editor Date Revision Details

1.0 J. McB 30/03/2000 Initial Release Draft A A.G. June 2000 Partial re-format to Simoco Europe standard. Draft B P.N. 04/07/2000 Rev6 Schematics, UW Band & Appendix

updates

Draft C P.N. 31/07/2000 Still in progress – not to be released!

Updated with E0,AC,TK,UW rev7 schematics & layouts

Revised Block Diagram.

9010 mic, corrected alignment instructions Draft C5 A.G. 17-07-2000 Update to Draft C from Simoco Pacific. Draft D A.G. 27-09-2000 Amended text: Variants; Tech Spec & App B.

List of Associated Publications

Document No. Description Issued By

TNM-I-E-0005 SRM9000 Series Installation Instructions Simoco Europe TNM-U-M-0001 SRM9010 PMR/Trunk Operating Instructions Simoco Europe TNM-U-E-0013 SRM9020 PMR Operating Instructions Simoco Europe TNM-U-E-0014 SRM9025 PMR Operating Instructions Simoco Europe TNM-U-E-0015 SRM9025 Trunk Operating Instructions Simoco Europe TNM-U-E-0003 SRM9030 PMR Operating Instructions Simoco Europe TNM-U-E-0004 SRM9030 Trunk Operating Instructions Simoco Europe

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Table of Contents

1. INTRODUCTION............................................................................................................1

1.1 GENERAL........................................................................................................................1

1.2 SCOPE ...........................................................................................................................1

1.3 DESCRIPTION..................................................................................................................1

1.4 PRODUCT VARIANTS AND FACILITIES ...............................................................................2

1.5 GLOSSARY......................................................................................................................5

2. SERVICE PHILOSOPHY ...............................................................................................6

2.1 SERVICE CONCEPT .........................................................................................................6

2.2 WARRANTY.....................................................................................................................6

2.2.1 Service within and out of warranty........................................................................6

2.2.2 Ancillary Items.......................................................................................................6

2.3 SOFTWARE POLICY.........................................................................................................6

2.4 ADJUSTMENT AND ALIGNMENT.........................................................................................7

2.5 TECHNICAL SPECIFICATION..............................................................................................8

2.5.1 General .................................................................................................................8

2.5.2 Transmitter............................................................................................................9

2.5.3 Receiver..............................................................................................................10

2.5.4 Signalling.............................................................................................................11

2.5.5 Environmental.....................................................................................................12

3. TECHNICAL DESCRIPTION .......................................................................................13

3.1 RECEIVER.....................................................................................................................13

3.1.1 Front End Filters and RF Amplifier......................................................................13

3.1.2 First Mixer and IF Section...................................................................................13

3.1.3 Quadrature Demodulator....................................................................................15

3.1.4 Receiver Audio Processing.................................................................................15

3.2 TRANSMITTER...............................................................................................................15

3.2.1 Drivers and PA Stages........................................................................................15

3.2.2 Power Control .....................................................................................................17

3.2.3 Antenna Changeover and Harmonic Filter..........................................................17

3.2.4 Transmitter Audio Processing.............................................................................17

3.3 FREQUENCY SYNTHESISER............................................................................................19

3.3.1 General ...............................................................................................................19

3.3.2 PLL......................................................................................................................19

3.3.3 VCO ....................................................................................................................19

3.3.4 Negative Bias Generator and Loop Filter............................................................19

3.3.5 Phase Modulator.................................................................................................19

3.3.6 Reference Oscillator ...........................................................................................20

3.4 CONTROL .....................................................................................................................20

3.4.1 DSP and FPGA...................................................................................................20

3.4.2 DSP Clock Oscillator...........................................................................................22

3.5 MEMORY ......................................................................................................................22

3.5.1 Multiplexer...........................................................................................................22

3.6 POWER SUPPLIES.........................................................................................................22

3.6.1 Power On Function .............................................................................................22

3.6.2 Power Supplies...................................................................................................23

4. ALIGNMENT ................................................................................................................25

4.1 TEST EQUIPMENT ....................................................................................................25

4.2 TEST SET UP .................................................................................................................27

4.2.1 COMMS Set up...................................................................................................28

4.2.2 Radio Preparation...............................................................................................29

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4.2.3 ALIGNMENT PROCEDURE...............................................................................30

5. REPLACEABLE PARTS..............................................................................................39

6. CIRCUIT DIAGRAMS AND PARTS LIST....................................................................41

6.1 LIST OF ILLUSTRATIONS.................................................................................................41

List of Figures

Figure 3-1 VHF/UHF Receiver Block Diagram .......................................................................14

Figure 3-2 VHF/UHF Transmitter Block Diagram ...................................................................16

Figure 3-3 VHF/UHF Synthesiser, Block Diagram.................................................................. 18

Figure 3-4 VHF/UHF Control Block Diagram .......................................................................... 21

Figure 4-1 SRM9000 Programming & Alignment Breakout Box ............................................. 26

Figure 4-2 SRM9000 Speaker Output Breakout Box..............................................................26

Figure 4-3 Test Set up ............................................................................................................ 27

Figure 5-1 Replaceable Parts ................................................................................................. 39

Figure 5-2 Band-Specific Parts ...............................................................................................40

Figure 6-1 SRM9000 Block Diagram ...................................................................................... 42

Figure 6-2 DSP and FGPA Schematic.................................................................................... 43

Figure 6-3 Power Supply Schematic....................................................................................... 44

Figure 6-4E0 Receiver Circuit Schematic ............................................................................... 45

Figure 6-5E0 Transmitte Circuit Schematic ............................................................................ 49

Figure 6-6E0 Synthesiser - VCO Schematic........................................................................... 53

Figure 6-7E0 Synthesiser - PLL Schematic ............................................................................57

Figure 6-8 A/D Converter Schematic ...................................................................................... 61

Figure 6-9 D/A Multiplexer Schematic ....................................................................................62

Figure 6-10 I/O Connections Schematic ................................................................................. 63

Figure 6-11 SRM9000 PCB Layout, Top (1/2)........................................................................ 64

Figure 6-12 SRM9000 PCB Layout, Top (2/2)........................................................................ 65

Figure 6-13 SRM9000 PCB Layout, Bottom (1/2)................................................................... 66

Figure 6-14 SRM9000 PCB Layout, Bottom (2/2)................................................................... 67

List of Tables

Table 1-1 Common Features for All Variants............................................................................ 2

Table 1-2 Conventional-PMR Variants .....................................................................................3

Table 1-3 Trunked Variants ......................................................................................................4

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1. INTRODUCTION

1.1 General

The SRM9000 series of FM mobile radio transceivers is designed for conventional PMR and Trunked operation in VHF and UHF radio systems.

The system is available in a number of functional variants. Each variant uses the standard SRM9000 mobile transceiver, which is software configured for different control ancillaries. The software configuration together with the type of controller (Basic or Enhanced microphone, Handset, or Alphanumeric Control Head) determines the radio features for the different variants as follows.

PMR/Trunked

Basic Telemetry Transceiver No Display or Control Head SRM9005 Low Range Version with Basic Control Microphone SRM9010 Mid Range Version with Enhanced Control Microphone SRM9020 Handset Version with Alpha Display Handset SRM9025 System Level Remote Version with Alpha Display Handset SRM9030

1.2 Scope

This manual provides technical specifications, description and servicing details for the SRM9000 series of mobile radio transceivers together with the related microphones and control heads.

Unless specifically stated otherwise, the text and illustrations refer to all versions in the series.

1.3 Description

The design concept utilises wide band analogue techniques for RF transmit and receive circuitry with digital signal processing for narrow and wideband modulation and demodulation. Electronic tuning is used throughout the mobile to eliminate manual tuning and level adjustment.

A Digital Signal Processor (DSP) and a Field Programmable Gate Array (FPGA) are used with other dedicated devices in the SRM9000 to perform the following functions under software control:

• Frequency Synthesis of all operating frequencies.

• Modulation and demodulation of 12.5/20/25kHz FM signals on a per channel basis.

• Modem functionality for specified data modulation schemes.

• Filtering, pre-emphasis, de-emphasis, limiting, compression, muting, CTCSS, Selcall

or any other frequency or level dependent signal modification.

• Serial communications with the Control Ancillaries and Alignment Tool.

• Tuning Control data for TX and RX.

The SRM9000 Transceiver comprises a rugged extruded aluminium sleeve which houses a single printed circuit board assembly and provides all heatsinking requirements. The sleeve housing is closed at each end by high-impact plastic end caps; all cable ports and mechanical interfaces are sealed against moisture and dust ingress.

The PCB assembly comprises a single, multi-layer PCB containing all the RF and control circuitry. The PCB seats on an extruded aluminium tray that slides into the outer aluminium sleeve where it is secured with screws accessed from the outside of the case. Provision is made under the main PCB tray assembly for additional hardware options.

There are two installation options available for the SRM9000. The outer aluminium extrusion has side flanges which allow the mobile to be bolted directly to any flat surface in the vehicle. A quick release cradle is also available.

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1.4 Product Variants And Facilities

Product variants and facilities are detailed in Table 1-1, Table 1-2 and Table 1-3

Table 1-1 Common Features for All Variants

Feature: Model: 9005 9010 9020 9025 9030

Control

Display

Adjustable Display Illumination

Buttons and Keys

Speaker Frequency Bands

Channel Spacing Menu driven Customisable

Menus

None or Serial or

Display Microphone

Display

Handset Parallel if Option Brd

- 1 digit LED 6 digit LCD 2x12 char LCD 8x14 char

- Yes Yes - Yes

- Vol Up/Down

Select 1 Function

Vol Up/Down 4 Function

Vol Up/Down

6 Function

12 Keypad

Send/End

Menu + Scroll

- Yes Yes Yes Yes

66-88MHz, 136-174MHz, 174-235MHz, 335-400MHz,

400-450MHz, 440-500MHz, 470-530MHz

12.5/20/25kHz

- - - Yes Yes

Control Unit with Microphone

graphic LCD

6 Function

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Table 1-2 Conventional-PMR Variants

Feature: Model 9005 9010 9020 9025 9030

Channels Signalling

Attack Operation DTMF Encode PTT Limit Timer

with warning beeps

PTT Inhibit on Busy

Voting Scanning

Priority Scanning Nuisance Delete Multiax Mod/Demod Fctn Ignition Sense

Input VOX Handsfree General External

IO 600 Ohm Interface Internal GPS

10 10 100 1000 1000 CTCSS / DCS CTCSS / DCS

ANI

CTCSS / DCS Selcall

CTCSS / DCS Selcall + Phonebook

- Yes Yes Yes Yes

- - - Yes Yes

Yes

Yes 8 fixed groups 8 fixed groups 7 fixed, 1

4 fixed, 4 user 4 fixed, 4 user

user

Yes

- - - Yes Yes Yes Option - - - Yes

Option Option Option Yes Option Option Option Option Option Option

Option Option Option Option Option Option Option Option Option Option

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Table 1-3 Trunked Variants

Feature: Model: 9005 9010 9020 9025 9030

Channels Frequency Bands Background Hunt and

Vote-Now MPT1343 dialstrings ANN Numbering Memories User Phonebook Alpha Status List SDM/EDMs NPDs Mod/Demod Fctn Attack Operation Ignition Sense Input VOX Handsfree General External IO 600 Ohm Interface

1024 channels in 50 sub-bands Specifically : 136-174MHz, 400-450MHz (and possible in all other bands) Yes Yes Yes Yes Yes

Yes Yes Yes Yes Yes

- Yes Yes Yes Yes 10 10 100 250 250

- - - Yes Yes

- - - Yes Yes Yes - - Yes Yes Yes - - Yes Yes Option - - - -

- Yes Yes Yes Yes Yes Yes Yes Yes Yes Option Option Option Yes Option Option Option Option Option Option Option Option Option Option Option

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1.5 Glossary

The following specific abbreviations are used in this handbook:

ADC Analog to Digital Converter AFC Automatic Frequency Control AGC Automatic Gain Control CODEC COde (Analog to Digital Converter) / DECode (Digital to Analog

Converter) integrated circuit. CTCS Continuous Tone Controlled Squelch System DAC Digital to Analog Converter DSP Digital Signal Processor FPGA Field Programmable Gate Array I The In phase baseband signal produced by the internal “I” mixer of

demodulator U401. PLL Phase Locked Loop PSD Peak System Deviation PMR Private Mobile Radio Q The Quadrature baseband signal produced by the internal “Q” mixer of

demodulator U401. This signal is 90° out of phase with the I signal. RSSI Receiver Signal Strength Indicator TCXO Temperature Compensated Crystal Oscillator

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2. SERVICE PHILOSOPHY

2.1 Service Concept

The SRM9000 series has been designed to provide low cost trunked and non-trunked analogue, mobile transceivers, using common core electronics, software and interfacing. It is a requirement that once the customer has purchased equipment, Simoco can follow this by providing an ongoing, high level of customer support together with a competitive and professional servicing activity.

There are three levels of service available:

LEVEL ACTIVITY RECOMMENDED

SPARES

1 Replacement of complete

transceiver/antenna/fuses Reprogramming

2 Replacement of PCB or

mechanical component replacement, Cosmetic repair

3 Repair by PCB or mechanical

component replacement, Cosmetic repair.

Repair of Radio PCB to component level in CRU.

Antennas, Fuses Ancillaries

Listed in Level 2 Spares Schedule

Radio PCB components only available to CRU.

RECOMMENDED TEST EQUIPMENT

Multimeter P.C. Radio software Programmer As above + service aids

and test equipment

As above + service aids and test equipment

2.2 Warranty

Initially, the normal 12-month warranty will apply to all radios and ancillaries.

2.2.1 Service within and out of warranty

The field Service Level for the SRM9000 mobile is LEVEL 2, PCB replacement. LEVEL 2 service, PCB (only) and case part replacement, will be carried out in field repair

workshops, or the Central Repair Unit (CRU) if required. LEVEL 3 Service (Radio PCB component level repair) will ONLY be carried out in the Central

Repair Unit. For this, the complete radio must be returned to the CRU. A PCB replacement program may be offered by the CRU in some countries.

2.2.2 Ancillary Items

All ancillary items (except remote alphanumeric control head) are Level 1 service. These items should be replaced if faulty; they are non-repairable, and non-returnable to the CRU.

2.3 Software Policy

Software provided by Simoco Europe shall remain the Company's property, or that of its licensors and the customer recognises the confidential nature of the rights owned by the Company.

The customer is granted a personal, non-exclusive, non-transferable limited right of use of such software in machine-readable form in direct connection with the equipment for which it was supplied only. In certain circumstances the customer may be required to enter into a separate licence agreement and pay a licence fee, which will be negotiated at the time of the contract.

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The customer undertakes not to disclose any part of the software to third parties without the Company's written consent, nor to copy or modify any software. The Company may, at its discretion, carry out minor modifications to software. Major modifications may be undertaken under a separate agreement, and will be charged separately.

All software is covered by a warranty of 3 months from delivery, and within this warranty period the Company will correct errors or defects, or at its option, arrange free-of-charge replacement against return of defective material.

Other than in clause above, the Company makes no representations or warranties, expressed or implied such, by way of example, but not of limitation regarding merchantable quality or fitness for any particular purpose, or that the software is error free, the Company does not accept liability with respect to any claims for loss of profits or of contracts, or of any other loss of any kind whatsoever on account of use of software and copies thereof.

2.4 Adjustment and Alignment

There are no internal adjustments in the SRM9000. Re-programming and alignment is done with the unit installed using software tools. For servicing, the radio PCB can be operated as a stand alone unit provided a temporary heatsink is fitted under the transmitter PA module for transmitter servicing and that the receiver audio output be kept below 100mW for receiver servicing. Radio performance is not adversely affected by operating without the outer sleeve but there will be some change to performance when the metal cans are removed from the RF sections of the board.

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2.5 Technical Specification

2.5.1 General

Operation Single or two frequency simplex

Modulation

Frequency modulation (phase) F3E

Supply Voltage Requirements

10.8 to 16.2V DC negative earth (13.8V nom.)

Current Consumption

Mobile With Control Mic

Radio off Standby(squelched):

RX Audio O/P: 300mW (not bridged)

4.0W

≤ 5mA ≤ 5mA ≤ 5mA ≤ 200mA ≤ 210mA ≤ 210mA*

≤ 450mA ≤ 470mA ≤ 500mA * ≤ 1200mA ≤ 1220mA ≤ 1250mA*

Mobile With Alpha Mic

Mobile With Alpha Head

Transmit: 25W 1W *Add 250mA to current consumption for Alpha Head with backlight on.

Frequency Bands

Band Frequency Range Band Frequency Range

E0 66 - 88 MHz R1 335 - 375MHz

AC 136 - 174MHz R2 370 - 400MHz

K1 174 - 208MHz TK 400 - 450MHz

KM 208 -245MHz UW 440 - 500MHz

Switching Bandwidth

Radio covers the complete band without retuning

Channel Spacing

12.5 / 20 / 25kHz

Frequency Stability

Better than ±2.5 ppm

Operating Temperature

-30°C to +60°C ambient

VHF UHF

≤ 6.5A ≤ 7.5A ≤ 2.0A ≤ 2.5A

WR 470 - 530MHz

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Dimensions (mm) Height Width Depth

Transceiver

9030 Alpha Control Head

9025 Alpha Display Handset

9020 Alpha Mic

9010/30 Microphone

Weight

Transceiver 1.8kg

2.5.2 Transmitter Power Output

High Power: 25W Adjustable down to 1W Low Power: 1W Adjustable up to 25W

Transmitter Rise Time

Less than 40 ms

56 65

165

96 82

170 188

52 68 57

165

45 30 44 38

Duty Cycle

1 minute transmit : 4 minutes receive

Spurious Emissions

< 0.25uW (9kHz to 1GHz) < 1.0uW (1GHz to 4GHz))

Residual Noise

60% deviation. CCITT Weighted 25kHz Channel Spacing >45dB

12.5kHz Channel Spacing >40dB

Audio Frequency Distortion

≤ 3% (at 60% deviation)

Audio Frequency Response

300 to 3000Hz* +1dB -3dB Figures apply for a flat audio signal or a 6dB/octave pre-emphasis curve (*2550Hz 12.5kHz channel spacing)

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2.5.3 Receiver

Sensitivity

≤ 0.3µV PD (-117.5dBm) for 12dB SINAD ≤0.4µV PD for 20 dB Quieting.

Adjacent Channel Selectivity

25kHz Channel Spacing >73dB

12.5kHz Channel Spacing > 65dB

Intermodulation Rejection

ETS Method > 65dB AS4295 Method> 70dB

Spurious Response Rejection

> 75dB

Blocking

> 95dB ( ±1MHz)

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Conducted Spurious Emissions

< 2nW (-57dBm) 9kHz to 4GHz

FM Residual Noise (CCITT weighted)

25kHz : > 45dB

12.5kHz : > 40dB

Mute Range

Typically 6 to 25dB SINAD Typical setting 10 to 12dB SINAD

Mute Response Time

<30mS (no CTCSS) add 200mS for CTCSS

Voting Response Time

tba

Audio Distortion

< 3% (1W / 4ohm, 60% modulation) <5% (4W / 4ohm, 60% modulation)

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Audio Frequency Response

350 to 3000Hz*, +1dB to -3dB (no CTCSS) 360 to 3000Hz*, +1dB to -3dB (with CTCSS) Figures apply for a flat audio response or a 6dB/octave de-emphasis curve (*2550Hz for 12.5kHz channel spacing)

2.5.4 Signalling

CTCSS

38 standard CTCSS tones are supported plus any non prescribed tones in the range 67 to

241.8Hz.

Frequency (Hz) Frequency (Hz) Frequency (Hz)

67.0 Hz

71.9 Hz

74.4 Hz

77.0 Hz

79.7 Hz

82.5 Hz

85.4 Hz

88.5 Hz

91.5 Hz

94.8 Hz

97.4 Hz

100.0 Hz

103.5 Hz

CTCSS Encoder Tone Deviation

Channel Spacing

25 kHz 20 kHz

12.5 kHz

SELCALL

The following tone sets are supported:

107.2 Hz

110.9 Hz

114.8 Hz

118.8 Hz

123.0 Hz

127.3 Hz

131.8 Hz

136.5 Hz

141.3 Hz

146.2 Hz

151.4 Hz

156.7 Hz

250.3 Hz

Deviation

500 to 750 Hz 400 to 600 Hz 250 to 375 Hz

162.2 Hz

167.9 Hz

173.8 Hz

179.9 Hz

186.2 Hz

192.8 Hz

203.5 Hz

210.7 Hz

218.1 Hz

225.7 Hz

233.6 Hz

241.8 Hz

ST-500: CCIR, EEA, ZVEI, DZVEI, EIA ST500/CML: ZVEI_3, DZVEI CML: CCIR, EEA, ZVEI SIGTEC: CCIR, CCIRH, EEA, ZVEI_1, XVEI_2, ZVEI_3, NATEL, EIA SEPAC: CCIR, EEA, ZVEI_1, ZVEI_2, ZVEI_3, EIA Tone period: 20mS, 33mS 40mS, then 10mS steps to 2.55S.

Selcall Tone Deviation

6dB/octave pre-emphasis response, relative to 70% PSD at 2.4 kHz

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DTMF Tone Frequencies Tones 0-9, *, #. Tones 1209 Hz 1336 Hz 1477 Hz

697 Hz 770 Hz 852 Hz 941 Hz

2.5.5 Environmental Operational Temperature

-30°C to +60°C

Storage Temperature

-40°C to +80°C

Vibration Specification

IEC 68-2-6 with additional frequency acceleration from 60 – 150 Hz

Cold

IEC 68-2-1 Test 5 hours at -10°C

Dry Heat

IEC 68-2-2 Test 5 hours at +55°C

1 4 7 *

2 5 8 0

3 6 9 #

Damp Heat Cycle

IEC 68-2-30 Test 2 cycles at +40°C

Product Sealing

Main Radio Unit: IEC529 rating IP54 Microphones: IEC529 rating IP54 Remote Control Head IEC529 rating IP54

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3. Technical Description

3.1 Receiver

Refer Figure 3-1

3.1.1 Front End Filters and RF Amplifier

The receiver input signal from the antenna passes through the antenna filter comprising L10, L11, L12 and associated tuning capacitors. With the mobile in receive mode, diodes D3, D4 and D5 in the antenna switch are reverse biased allowing the receiver input signal to be coupled through to the front end with minimal loss. The overall insertion loss of the antenna filter and switch is approximately 0.8dB. Front end selectivity is provided by varactor tuned bandpass filters at the input and output of the RF amplifier.

Front end tuning voltages are derived from the alignment data stored in the radio. The DSP processes this data to optimise front end tuning relative to the programmed channel frequencies which may be changed at any time without re-aligning the radio.

To achieve the required varactor tuning range an arrangement of positive and negative bias power supplies is used to provide a total bias across the varactors of up to 14.0VDC. A fixed

2.5V positive bias derived from the 5.0V supply and voltage divider R425/426 is applied to the cathodes of the varactor diodes. The negative bias supply originates at the DSP/FPGA as a composite digital tuning signal (FE TUNE) containing the data for the four front end tuning values TUNE 1 to 4 for the particular channel frequency selected. The level is dependent on channel frequency and tuning and varies between +0.1 and +3.0V. This signal then passes through buffer U901A and level translator Q900 to Q903 where it is converted to a high level (-

0.5 to -11.5V) negative equivalent of the original signal. The -12.0V rail of the level translator is generated by U300B/C with D304 to D306 providing the required voltage multiplier effect. The high level negative signal is then split into the four individual front end negative DC values under software control by multiplexer U902 and associated storage capacitors C904 to C907 before being applied to the anodes of the front end tuning varactors.

The RF amplifier stage comprises a low noise transistor amplifier (Q400) which is compensated to maintain good linearity across the required frequency bands and temperature range. This provides excellent intermodulation and blocking performance across the full operating range. The gain of this stage is typically 17dB for both UHF and VHF versions.

3.1.2 First Mixer and IF Section

The output of the last front end bandpass filter is coupled into single balanced mixer T400/D413 which converts the RF signal to an IF frequency of 45MHz. The local oscillator injection level is typically +8dBm at T400 pin 1 with low side injection used for UHF and high side for VHF.

Following the mixer is IF amplifier Q401 which provides approximately 15dB of gain and in association with its output circuitry presents the required load conditions to the 4 pole 45MHz crystal filter Z401/402.

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Figure 3-1 VHF/UHF Receiver Block Diagram

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3.1.3 Quadrature Demodulator

Additional IF gain of approximately 30dB occurs at U401 which is a dedicated IF AGC amplifier/Quadrature Demodulator configured for single ended input and output operation. The AGC voltage for U401 is derived from the RSSI function of the DSP via AUX CTL and multiplexer U902. The onset of AGC operation occurs when RF input signal levels at the antenna exceed -90dBm.

Conversion of the 45MHz IF signal to I and Q baseband signals is carried out by the demodulator section of U401. The 90MHz local oscillator signal is generated by VCO Q402 which is phase locked by the auxiliary PLL output of U701 via feedback signal AUX LO2.

3.1.4 Receiver Audio Processing

All receiver audio processing and filtering functions are performed by the CODEC U800 under the control of the DSP. The receiver I and Q analog baseband signals are converted to digital signals by the CODEC ADC before being applied to a series of digital filters which provide the final stage of adjacent channel filtering, high pass and low pass filtering and mute noise processing for narrow and wideband operation. The processed signals are then converted to analog audio signals by the CODEC DAC and are applied to conventional audio amplifiers U803A/B and the speaker amplifier U5.

There are two speaker options available. A half bridged configuration using a speaker across balanced output SPKR OUT1 and 2 which provides an audio output level of up to 4 watts into 4 ohms. The other option is a full bridge configuration using a high power speaker across SPKR OUT1 and 2 and providing an audio output level of up to 10 watts into 8 ohms. The carrier and signalling mute functions are performed by Q810/811/813 under DSP control with additional receiver muting to U803B being applied by U103C when the mobile is in transmit mode. Deemphasis to the audio PA U5 is performed by R43 and capacitors C42 to C58. Flat audio is provided to S1-6 via amplifier U803A.

3.2 Transmitter

Refer Figure 3-2.

3.2.1 Drivers and PA Stages

The RF output level from the VCO buffer Q604 is typically +5dBm (UHF) and +8dBm (VHF). TX buffer Q606 increases this level by approximately 3dB (UHF) and 11dB (VHF) and also provides additional VCO isolation. The following section of the TX buffer Q612 is controlled by the transmitter power control loop and Q609. Q609 is normally saturated in transmit mode so there is no minimum gain control applied to this stage. The gain of Q612 is typically 10dB (UHF) and 15dB (VHF) but the output level is reduced by input and output resistive attenuators to limit the PA driver input level to typically +20dBm. The gain of PA driver Q12 is controlled by the power control loop to ensure that transmitter output power remains within defined limits. The PA driver output level is typically +25dBm. PA module U2 utilises three stages (UHF) and two stages (VHF) to achieve the required final RF output power level of +44dBm (25 watts). Power output settings are derived from alignment data stored in flash memory during the initial factory alignment. The DSP processes this data to optimise the power output level relative to the programmed channel frequencies which may be changed at any time without retuning the radio. .

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Figure 3-2 VHF/UHF Transmitter Block Diagram

An active filter comprising Q14, 17,18 and 19 provides isolation to minimise power supply noise at the PA. This is achieved by maintaining a voltage differential of approximately 1V across Q14 and indirectly filtering its gate voltage. Q14 is switched on only during transmit via R523 to minimise receiver power requirements.

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3.2.2 Power Control

Output power is stabilised by a power control feedback loop. L1, R54, a printed circuit transmission line, D6 and associated components comprise the power detector with Q3/10, U3 and associated components providing the power setting and control sections. Forward and reverse power is sampled by the power detector and applied as a DC voltage to the inverting input of comparator U3A. The TX PWR SET voltage which is a DC voltage proportional to the programmed TX power setting is applied to the non-inverting input of the comparator. PA module output level changes due to supply voltage, load or temperature variations are detected and applied to the comparator which proportionally adjusts the PA driver (Q12) supply, and therefore the PA drive level, via Q10/Q3. High temperature protection is provided by thermistor R452 which progressively reduces the power level if the PA module temperature becomes excessive. Q15 and Q16 provide for dual power control time constants necessary for good power ramp and decay characteristics.

3.2.3 Antenna Changeover and Harmonic Filter

The antenna changeover circuit consisting of pin diodes D3/D4/D5 is switched by Q4/Q8/Q11 and associated circuitry allowing the transmitter output to be coupled to the antenna while providing isolation for the receiver input. With the transmitter switched on, the diodes are forward biased allowing power to be coupled through to the antenna and isolating the receiver by grounding its input at C28. The short circuit at the receiver input is transformed to an effective open circuit at D3 by L13, which minimises transmitter loading. With the transmitter switched off the diodes are reverse biased allowing the receiver input signal to reach the receiver front end with minimal loading and loss.

The harmonic rejection low pass filter comprises L10/11/12 and associated capacitors.

3.2.4 Transmitter Audio Processing

Microphone audio input signals of 40mV RMS with a source impedance of 470 ohms are provided at the microphone input (AUD IN1) by an external microphone unit comprising an electret microphone insert and a preamplifier with a gain of 18dB. U108 is a control gate for the microphone audio signals.

AUD IN2 is the external audio options and data input which is controlled by gate U107. Inverter Q20 ensures that the data or audio options signals are muted when the mic. audio gate is active. The AUD IN2 input level and source impedance is the same as the microphone input.

Q812 is a unity gain amplifier which provides buffering of the audio and data signals. U103B provides CODEC input switching which selects either the receiver I signal or transmitter audio/data signals depending on the TX/RX mode. All pre-emphasis, filtering, compression and limiting processes for narrow and wideband operation are carried out in the CODEC (U800) under the control of the DSP. The processed transmitter audio/data from the CODEC output at VOUTL is applied to the VCO as a modulation signal with a level of approximately 200mV P/P.

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3.3 Frequency Synthesiser

3.3.1 General

Refer Figure 3-3 The SRM9000 frequency synthesiser consists of individual transmitter and receiver (local

oscillator) voltage controlled oscillators, loop filter, varactor negative bias generator, reference oscillator and an integrated, dual phase locked loop device U701.

3.3.2 PLL

The PLL device contains two prescalers, programmable dividers and phase comparators to provide a main and auxiliary PLL. The main PLL of U701 controls the frequency of the TX/RX VCOs via Control Voltage outputs at pins 2 and 3 and VCO Feedback to pin 6. The auxiliary PLL is used to control the receiver 90MHz second local oscillator via the Control Voltage output at pin 17 and VCO Feedback to pin 15. The PLL operation involves the division of the 14.4MHz reference oscillator frequency by divider U710 and the internal divider of U701 down to a lower frequency which corresponds to a sub-multiple of the radio channel spacing ie. 6.25kHz for

12.5/25kHz channel spacing or 5kHz for 20kHz channel spacing. The VCO frequency is sampled and divided down to the same frequency after which it is phase compared to the reference. Any error produces an offset to the Control Voltage output which is used to correct the VCO frequency. A valid lock detect output is derived from pin 20 and is sampled by the FPGA during transmit. If an unlocked signal is detected the radio will switch back to receive mode.

3.3.3 VCO

The transmitter and receiver VCOs use low noise JFET transistors (Q600 RX, Q602 TX) and inductors L602 (RX), L608 (TX) to generate the signals for the required band coverage. Electronic tuning is provided by varactor diodes D600 to D608 with their control voltages derived from the Loop Filter, PLL and Negative Bias Generator.

VCO selection and timing is controlled by the DSP via the RX and TX power supplies and applied through switches Q601 (RX) and Q603 (TX). VCO buffer Q604/605 isolates the VCO from load variations and active power supply filter Q615 minimises supply related noise. A PLL feedback signal is sampled from the VCO buffer output via buffer Q607.

3.3.4 Negative Bias Generator and Loop Filter

A positive and negative varactor bias supply similar to the front-end varactor arrangement has been used to achieve the required broadband tuning range of the VCOs. PLL device U701 is programmed to deliver a fixed nominal +2.5V output from phase detector/charge pump CPPF or CPP (selection depends on radio setup) regardless of the channel frequency selected. This voltage is filtered to remove synthesiser noise and reference products by loop filter C719/722/734 and R721/724/734. The resulting low noise voltage is applied to the cathode side of the VCO varactor tuning diodes as a positive bias voltage. The negative bias supply originates as a positive DC voltage (0.1V to 3.0V) at the DAC output of U701 (DOUT) with a level relative to the programmed state of the radio (eg. channel frequency, TX/RX state). The voltage is converted to a high level negative supply by VCO Varicap Negative Supply Q700 to Q703. The -17V rail of this supply is generated by U300B/C with D304 to D307 providing the voltage multiplying effect needed to achieve -17V. The output of the negative supply is applied directly to the VCO varactor anodes as the negative tuning voltage VCAP BIAS.

3.3.5 Phase Modulator

The modulation path for audio, data and higher frequency CTCSS signals is via D609 and its associated components in the TX VCO. The reference input to the PLL (FXTAL) provides the low frequency modulation path in conjunction with phase modulator Q714 to Q716. U711A is a low pass filter which provides 6dB per octave attenuation to frequencies above approximately 180Hz. Modulation balance adjustment is carried out using a CODEC generated 100Hz square wave applied to TX MOD1. A DAC output from the Alignment Tool is applied to buffer U711B and ramp generator Q711 to Q713 via the TUNE BAL line to adjust the low frequency modulation level.

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3.3.6 Reference Oscillator

TCXO U700 determines the overall frequency stability and frequency setting of the radio. The frequency setting is achieved by adjusting its ADJ voltage with the Alignment Tool. In addition, the ADJ input is used in a frequency control loop with the receiver I and Q signals to provide receiver AFC. U700 operates at 14.4MHz and is specified at ±2.5ppm frequency stability over the temperature range -25° to +75°C.

3.4 Control

Refer Figure 3-4

3.4.1 DSP and FPGA

The SRM9000 transceiver operates under the control of a DSP (U102) and FPGA (U106) combination which together with a number of other dedicated devices perform all the operational and processing functions required by the radio. The FPGA is configured by the DSP under software control to provide the following functions:

• Channel set-up of all operating frequencies

• Modulation processing and filtering

• De-modulation processing and filtering

• TX power output reference

• Receiver front end tuning

• Serial communications with alignment tool, microphone and control head

• Modem functionality for data modulation

• All signalling / CTCSS generation and decoding

• CO control

• Receiver muting control

• TX / RX switching

• PLL detect

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