LM LMC30051 User manual

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.. linear modulation technQ/ogy
m
SERVICE ·MAN.UAL
. . . . .
'.
. . .
F:,OR THE L ' M ' REPE~TJ:R SITE (BASE STAn .ON)
(25 WATT AND :· 100 ·· WATI)
. '" , "
Linear Modulation Mobiie&dio System
Advanced Pigit8J'Net-work,. Trunking .
Part ·Nos. LMC30051·mid:LMC30052
: . .
\
,
, ~uricor "-lioco~ Umlted
.' Cross Keya Houae .. .
Westfield industrial Eatate .
Mldsomer Norton ... ..'; :. .
Bath BA3 4BS England .
Tel.phone [phone] .'
Fax +44 (0)17&1 41~1
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Publication Reference SM/02/1.2
December 1995 '
Printed in England

~ ________________ ' _ " _ ' _ ' _ ''' _-_ - '' _ ' : ' _ ' ~ ' _____________________ L_I_C_~_N_C_E
• DO NOT use this equipment near unshielded electrical blasting caps
or
in an explosive atm..Q~phere .
.,, _ .. ,_ .. .- .. ...
• The lOOW PA unitU~d30052) uses power transis~rs that contain
beryllium
oxid~ ,,; wh,ich is extremely toxic. The power transistors are
identified
as TR6 041:806:.2 and TR7 015106-2. .
In the unlikel~ . ev~nt : of.coniing into contact with beryllium oxide,
wash thoroughly with soap and water, if skin is broken obtain
medical attention. If eye. -cc;mtact, wash for 15 minutes with running
water including' under · the .eyelids, and seek medical attention.
Ifingested or fuh:EU ' ed~seek medical atten~ion immediately.
. ". ': ' ... :. ~ . . .' .. .
~. ' . ~ . .'~ j ;' -: :' ~' . ::
Repairs, Modifications and ': Maintenance .
•
•
•
.: ' ~.
•• J. •
If any operational difficulties arise while using this product, report
them to autho~e~ . ~~ · . personnel as soon as possible.
This
system con~ rio-h~er serviceable pa.rts". Unauthorized
adjustments or modifications will void the warranty and may lead to
emissions outside FCC limits.
DO NOT connect an e~mal poweramplif'ier to this equipment.
,.
.," ~
I, ' .
..! .. - ::' : ,:.. :...
: .\. .
.. ... "
\ , "- .
.. ...
LICENC~ : 8ceON'fENTS -LM REPEATER SITE SERVICE MANUAL iii
. . . - ... ""- .- ,

Q LMC30051/LMC30052 SPECIFICATIONS
~--------------------
1. LMC30051/LMC30052 Specifications
The following specifications are intended for testing and servicing the
Repeater. Specifications are subject to change without notice.
1.1 General
Operating Mode
Frequency Range
Receive
Transmit
TransmitlReceive Separation
Channel Spacing
Channel Increment
Supply Voltage
Full Duplex
221-222 MHz
220-221 MHz
1 MHz
5kHz
2.5 kHz
240 VAC 110 V AC
Current Drain (typical, std test signal)
Transmit 25 W 0.34 A 0.70 A
1.52 A
0.33 A
Transmit 100 W 0.71 A
Receive 0.19 A
Temperature Range
Operational
Storage
Dimensions
Width
Depth
Height
Weight
Approvals
Audio Frequency Response
1.2 Receiver
Sensitivity
20dBSINAD
12dBSINAD
Selectivity
Intermodulation
Spurious and Image Rejection
Distortion
RF Input Impedance
Frequency Stability
-30°C to +55 °C
-40 °C to +85 °C
482mm
360mm
177mm
12.02 kg
(19.0")
(14.2")
(1.95")
(26.45Ib)
FCC
Part 15, 90
±0.75 dB, 300 Hzto 3 kHz
< -107 dBm, typically -112 dBm
< -115dBm
> 50 dB at 5 kHz
65 dB
70 dB
3%
50 n ,unbalanced to ground,
maximum VSWR 2:1
± 0.1 ppm
SECTION ONE -LM REPEATER SITE SERVICE MANUAL
1-1

LMC30051/LMC30052 SPECIFICATIONS
e
1.3 Transmitter
RF Output Power, Nominal
(Peak Envelope Power)
25W
100W
RF Output Power, Minimum
(Peak Envelope Power)
1W 4W
Spurious & Harmonic Emissions -61 dBc -67 dBc
(S 250 kHz from Channel
centre. Reference largest
in
channel signal in 100 Hz
bandwidth)
Spurious & Harmonic Emissions -69 dBc -75 dBc
(~ 250 kHz from Channel
centre. Reference largest
in
channel signal in 10 kHz
bandwidth)
Audio Modulation
4KOOJ3E
RF Load Impedance 50 n, unbalanced to ground
Frequency Stability :t 0.1 ppm
1.4 Frequency Standard
OutputLevel
3±2dBm
Input Level
0±10dBm
Frequency 10.000
MHz
Frequency Stability
:to.l ppm
1-2
SECTION ONE -LM REPEATER SITE SERVICE MANUAL

~ CONTENTS
~-------
Contents
1. I...MC300511IMC30052 Specifications ............................................................ 1-1
1.1 General .................................................................................................. 1-1
1.2 Receiver .................................................................................................. 1-1
1.3 Transmitter ............................................................................................ 1-2
1.4 Frequency Standard .............................................................................. 1-2
2. In.troduction .......................................................................................................2-1
2.1 Scope of Manual ..................................................................................... 2-1
2.2 Definitions ............................................................................................. 2-1
2.3 Reference Documents ............................................................................ 2-1
2.4 Related Docu.ments................................................................................ 2-2
2.5 Equipment Description ......................................................................... 2-2
2.5.1 Channel Shelf.............................................................................................. 2-2
2.5.2 Frequency Standard................................................................................... 2-3
2.5.3 Combining System....................................................... .. ............................. 2-3
2.5.4 System Control Interface ......................................... .. .......................... .. .... 2-4
2.5.5 System Control and Monitoring................................................................. 2-4
2.5.6 System Options........................................................................................... 2-4
2.6 On-Site System Testing ......................................................................... 2-5
3. Linear Modulation .. ~ ........................................................................................ 3-1
3.1 Definition ............................................................................................... 3-1
3.2 LM Methods ........................................................................................... 3-1
3.2.1 TransparentTone In Band......................................................................... 3-1
3.2.2 Feed Forward Signal Regeneration........................................................... 3-1
3.2.3 Cartesian Loop ......................................................................................... ... 3-2
3.3 Transmission Process ............................................................................ 3-2
3.4 Cartesian Loop Linearisation of the Transmitter ................................ 3-4
3.5 Reception Process.................................................................................. 3-5
4. Advanced Digital Network TnJDking (ADN'r) ........................................... 4-1
4.1 Control Channel .................................................................................... 4-1
4.2 Call Setup and Clear Down ................................................................... 4-1
5. Controls, Indicators and Displays ................................................................ 5--1
5.1 System Control Interface ...................................................................... 5-1
5.1.1 The Keypad ................................................................................................. 5-2
5.1.2 On-Site Functions....................................................................................... 5-2
5.2 Power ..................................................................................................... 5-4
5.3 PA:LED .................................................................................................. 5-4
5.4 TCC :LEDs.............................................................................................. 5-4
5.4.1 Prl' ................................................. .. .......... ................................................. 5-5
5.4.2 CW LOCK (Code Word Lock)..................................................................... 5-5
5.4.3 TALK .............................................. .... .... ............................................. .. ...... 5-5
5.4.4 IN SERVICE............................................................................................... 5-5
5.4.5 SQUELCH................................................................................................... 5-5
5.5 TCC Display ........................................................................................... 5-5
5.5.1 Power Up Sequence .................................................................................... 5-5
5.5.2 Failure Codes .. .................. .. ........................................................................ 5-6
LICENCE & CONTENTS -LM REPEATER SITE SERVICE MANUAL v

CONTENTS ~
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5.5.3 Normal Operation (Control Channel) ....................................................... fH)
5.5.4 Normal Operation (Traffic Channel) ........................................................ fH)
5.6 TCC Internal Controls........................................................................... 5-7
5.6.1 S10 Bus Address ........................................................................................ 5-7
5.6.2 Channel Number ........................................................................................ 5-7
5.6.3 FFSK Output Level.................................................................................... 5-8
5.7 TCC Front Panel Controls..................................................................... 5-8
5.7.1 Squelch Level ............................................................................................. 5-8
5.7.2 FFSR Threshold Level............................................................................... 5-9
5.7.3 Pilot Pumping ............................................................................................. 5-9
5.8 Frequency Standard .............................................................................. 5-9
5.8.1 IntemallExtemal Select............................................................................ 5-9
6. In.s1;allation......................................................................................................... 6-1
6.1 Perfonnance Tests ................................................................................. 6-1
6.2 Power Supply......................................................................................... 6-1
6.3 Location ................................................................................................. 6-1
6.4 System Control Interface ...................................................................... 6-2
6.4.1 System Control Terminal (Syscon) or Central Computer ........................ 6-2
6.5 Channel Setup ....................................................................................... 6-3
6.6 Repeater Rack........................................................................................ 6-3
6.6.1 Frequency Standard ................................................................................... 6-4
6.6.2 Channel Shelves......................................................................................... 6-5
6.6.3 Earth Connection....................................................................................... 6-6
6.7 Combining Rack (optional).................................................................... 6-6
6.7.1 Cavity Alignment ....................................................................................... 6-6
6.7.2 Receiver Connections................................................................................. 6-6
6.7.3 Transmitter Connections........................................................................... 6-7
6.7.4 Antenna Connection .................................................................................. 6-7
6.7.5 Earth Connection...................................................:................................... 6-7
7. Operation........................................................................................................... 7-1
7.1 Power Up ............................................................................................... 7-1
7.2 Control Channel Selection .................................................................... 7-1
7.3 Squelch Setting ...................................................................................... 7-2
7.4 During a Call ......................................................................................... 7-2
8. Circ11it Description .......................................................................................... 8--1
8.1 Receiver.................................................................................................. 8-1
8.2 Exciter and Power .Amplifier................................................................. 8-2
8.3 Trunking Channel Controller ............................................................... 8-4
8.4 Power Supply Unit ................................................................................ 8-5
8.5 Frequency Standard .............................................................................. 8-5
~ S,Ystem Control Interface ...................................................................... 8-5
'--"" 8.6.1 Main Bo8l'd................................................................................................. 8-6
8.6.2 RAM Banks ................................................................................................ 8-6
8.7 The I2C Bus............................................................................................ 8-7
8.7.1 Commands.................................................................................................. 8-7
8.7.2 Responses ................................................................................................... 8-7
9. Commissioning .................................................................................................. 9-1
9.1 Range ..................................................................................................... 9-1
9.2 Transmission Losses ............................................................................. 9-1
9.3 Receiver Losses...................................................................................... 9-1
9.4 Reciprocity............................................................................................. 9-2
10. Simplified. On·Site Testing ........................................................................ 10--1
10.1 Test Equipment ................................................................................. 10-1
vi
LICENCE & CONTENTS -LM REPEATER SITE SERVICE MANUAL

~ CONTENTS
~--------------------
10.2 Frequency Reference ......................................................................... 10-1
10.3 Receiver Sensitivity Tests ................................................................. 10-2
10.3.1 Setting up the Equipment ...................................................................... 10-2
10.3.2 MeasuringReceiver Sensitivity............................................................. 10-2
10.3.3 Receiver Testing via Splitter/Amplifier................................................. 10-6
10.3.4 Returning Equipment to Operation....................................................... 10-6
10.4 Transmitter Tests .............................................................................. 10-7
10.4.1 Transmitter Testing, Direct Connection............................................... 10-7
10.4.2 Transmitter Testing, Connection via Transmitter Combiner.............. 10-8
10.4.3 Returning Equipment to Operation....................................................... 10-9
10.4.4 Carrier Wave Identification (CWID) ..................................................... 10-9
11. Comprehensive OD.·Site TestiD.g............•..................................................11-1
11.1 Test Equipment ................................................................................. 11-1
11.2 Frequency Standard .......................................................................... 11-1
11.3 Test Modes ......................................................................................... 11-1
11.3.1 Transmit Preamble................................................................................. 11-2
11.3.2 Transmitter Test Modes.........................................................................11 -2
11.3.3 Transmitter PowerAdjust ..................................................................... 11-2
11.4 Receiver Tests .................................................................................... 1 1-2
11.4.1 Connections............................................................................................. 11-2
11.4.2 mtimate SINAD Test............................................................................. ll-3
11.4.3 Sensitivity Test....................................................................................... 11-3
11.5 Transmitter Tests .............................................................................. 11-3
11.5.1 Connections............................................................................................. 11-3
11.5.2 SpectrumAnalyzer Set-up..................................................................... 11-3
11.5.3 Stability: Pilot Only Test ........................................................................ ll-4
11.5.4 Linearity: Two Tone Test....................................................................... 11-4
11.5.5 Image Suppression: OneTone Test .......................................................11-5
11.5.6 External Signal Test ............................................................................... 11-6
11.5.7 Adjusting TransDrit Power..................................................................... 11-6
12. ChaD.nel Freq,uencies .....................................................................•............. 12-1
13. Base Station 5·Channe125/100 W.............................................................. 13-1
14. System Controlln:terface ..............................................•............................ 14-1
15. 10 MHz Frequency sUndard. .................•.....•..........................•.................. 15--1
16. ChaD.nel Shelf 25 W/ 100 W......................................................................... 16--1
17. Power .Am.pli:fier 25 W.............•................•..................•...••........................... 17-1
18. Power .Am.pli:fier 100 W................................................................................ 18-1
19. TnJDkjng ChaD.nel Controller ................................................................... 19--1
20. Channel Receiver Unit ................................................................................ 20-1
21. Channel Exciter Unit ..................•................................................................ 21-1
22. 200W Power Supply Unit ............................................................................ 22-1
23.·400W Power Supply Unit ............................................................................ 23-1
LICENCE & CONTENTS -LM REPEATER SITE SERVICE MANUAL
vii

CONTENTS ~
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Amendment Schedule
Amendments to this manual will be issued to incorporate changes or detail additional
information.
Amended pages will be identified by the amendment date and number
shown at the foot of the page. Record incorporation of amendments to this manual on this
page.
If a new issue of this manual is made all amendments will be incorporated.
Date Amdt.No.
Date Incorporated Reason for Change
If you find any errors or omissions in this manual, or you have any suggestions for
improvements please
write to the address shown on the front of this manual.
;
viii LICENCE & CONTENTS -LM REPEATER SITE SERVICE MANUAL

Q INTRODUCTION
~----~--
2. Introduction
2.1 Scope of Manual
This service manual contains installation, operation and service
information for
the Linear Modulation Technology Limited Repeater
Site. This manual applies to both 25 W (LMC30051) and 100 W
(LMC30052) equipment.
2.2 Definitions
ADNT
AGC
CCITT
CTU
DSP
DTMF
FFSR
FPU
12C
PABX
PSTN
PTI'
RFU
SCL
SDA
SDM1
SDM2
SINAD
SPU
TCC
TTIB
VSWR
Advance Digital Network Trunking
Automatic Gain Control
ConsultatifCommittee
Internationale Telephones et
Telecommunications (now ITU)
. Control
and Trunking Unit
Digital Signal Processor
Dual Tone Multiple Frequency
Feed Forward Signal Regeneration
Front Panel Unit
Inter-Integrated Circuit (bus).
Private Automatic Branch eXchange
Public Switched Telephone Network
Press To Talk
Radio Frequency Unit
Serial clock
Serial data
Short Data Message Type 1
Short Data Message Type 2
Signal/Noise
and Distortion
Signal Processing Unit
Trunking Channel Controller
Transparent Tone In Band
Voltage Standing Wave Ratio
2.3 Reference Documents
MPT1327 A Signalling Standard for Trunked Private and Land Mobile
Radio Systems (Radiocommunications Agency (UK».
MPT1343 System Interface Specification for Radio Units to be Used
with Commercial Trunked Networks Operating in Band ITI
and Sub-Bands 1 and 2. (Radiocommunications Agency (UK».
MPT1376 Co-existence Standard for Transmitters and Receivers
Operating
in 5 kHz Channels (Radiocommunications Agency
(UK».
SECTION TWO -LM REPEATER SITE SERVICE MANUAL
2-1

INTRODUCTION Q
----------~
2.4 Related Documents
• LMM 3115 Mobile Service Manual (SM/01f2.0)
• SYSCON
Manual (TUl211.4)
• TrunkingTechnical Reference Manual (TU13/1.1)
2.5 Equipment Description
2-2
The Repeater Site is part of the LM trunked radio system which allows
mobiles to communicate using 5
kHz channel assignments. A modulation
scheme called
Linear Modulation is used, which is spectrally efficient
and provides a medium particularly suited to the varying propagation
effects (e.g.
multipath and Doppler) encountered in a typical mobile
environment.
The system is designed for speech and data use, with data
rates of 14,400 bits per second achievable.
The
repeater employs digital signalling and provides trunked operation
using
the Advanced Digital Network Trunking (ADNT) system, based on
the UK specification MPl'1327. The unit provides features such as
Status Calls, Call Queueing, Priority Calls, Data Calls, Emergency
Calls, Group Calls, Individual
Calls and Telephone Connection.
The system
is completely modular, allowing easy expansion from a
simple local system,
to a large multi-channel, multi-site network.
Channels
may be added or removed with the system 'live', and the
system will automatically re-configure itself to use the new equipment.
Up to 24 channels can be accomodated on a single site. Single site
installations
can be upgraded to multi-site by adding a Central Control
Computer.
Up to 10 sites can be linked in this way.
The system is fully automatic, and can operate unattended. It canbe
remotely controlled using a Control Terminal connected via a modem
and telephone line. Refer to the SYSCON Manual (TUl211.4) for details
of operation of the Control Terminal.
The Repeater Site consists of, as a minimum, the following equipment
mounted in standard 19 inch cabinets:
• Up to 24 Channel Shelves
• Frequency Standard (a minimum ofone per 5-channel rack)
• System Control Interface (SCI)
• Combining
and Duplexing System.
2.5.1 Channel Shelf
A channel shelf consists ofa two-frequency duplex radio channel which
provides base
to mobile communication and a talkthrough connection for
mobile to mobile, along with
trunking signalling and control. It operates
on
the 200 channels in the 220 MHz band (220-221 MHz repeater
transmit, 221-222 MHz repeater receive). It is a 4U high unit, consisting
of five modules which can be removed independently from the shelf.
SECTION TWO - LM REPEATER SITE SERVICE MANUAL

Q INTRODUCTION
~--------------------
• Receiver Module
Receives radio frequency signals from LM mobiles, demodulates the
resulting Transparent Tone In Band (TTIB) signals, corrects for
fading
and Doppler effects using Feed Forward Signal Regeneration
(FFSR), and passes the recovered audio signal to the TCC. It is
controlled
by the TCC via an 12C bus.
• Trunking Channel Controller
Responsible for controlling the radio modules, generating and
interpreting trunking signalling, and routing audio signals. It also
forms
part of the distributed processingfor the trunking system. All
the TCCs in a site are connected together, and to the System Control
Interface by a
high speed Serial 110 bus.
• Exciter Module
Takes an audio output from the TCC, produces from it a baseband
TTIB signal,
and directly converts it up to the transmit frequency for
driving
the PA It uses a feedback signal from the PA to linearise the
amplifier using a technique known as Cartesian Loop Linearisation.
The whole operation of the exciter is controlled by the TCC via an 12C
bus.
• Power Amplifier
Takes the RF signal from the Exciter and amplifies it to a level
suitable for
radiation from an antenna. A feedback loop to the Exciter
makes the transmitter highly linear, to meet statutory near-channel
radiation specifications. It is available in 25 W and 100 W Peak
Envelope Power (PEP) ratings.
• Power Supply Unit
This is a switched-mode power supply which converts AC supply to
DC. The 100 W power
amplifier requires 28 V and 14 V DC. All the
other modules require 14 V DC. It is available in two power ratings.
The 200 W version is for use with the 25 W PA, and the 400 W version
is for use with the 100 W PA
2.5.2 Frequency Standard
This is a precision frequency standard containing an ovened oscillator,
which
generates a highly stable (0.1 ppm) 10 MHz frequency reference
from which
all the RF local oscillators are derived. All the local
oscillators
within the Receiver and Exciter modules are locked to this
reference. The unit provides 11 outputs so that it can drive 5 channels,
and have a spare output for connection to test equipment, or chaining to
other racks. It also has an input allowing it to be locked to an external
reference for improved
stability or chaining.
2.5.3 Combining System
The Combining System combines together the outputs of all the channel
power amplifiers providing
transmitterltransmitter isolation to reduce
intermodulation effects.
It also provides transmitterlreceiver isolation
(duplexing)
to prevent blocking of the receivers. It comprises a Circulator
and Tuned Cavity for each transmit channel, a Transmit DuplexFilter,
a Receive Duplex
Filter, and a Receive Signal Amplifier (RSA) which
SECTION TWO - LM REPEATER SITE SERVICE MANUAL
2-3

I .
INTRODUCTION Q
-----------------'J/!f)
2-4
includes a band-pass filter. The combining system is mounted in a
separate rack.
2.5.4 System Control Interface
The SCI controls the authorization ofusers onto the system, the
collection of billing data, control of system parameters, and general
system monitoring. It is usually controlled using SYSCON. Refer to the
SYSCON Manual (TUl211.4) and Trunking Technical Reference Manual
(TU13/1.1) for details of the operation of the SCI.
2.5.5 System Control and Monitoring
The system can be monitoredremotely, or locally using the SYSCON
program. SYSCON can monitor multiple sites (up to 10), records failures
and can be used to generate automatic alarms.
2.5.6 System Options
A single repeater rack can be supplied with between 1 and 5 channel
shelves. A
site can have up to 24 channels, so a large system will require
several
racks. Each rack needs its own frequency standard, and these
must be lockedtogether using the external input connector.
The PA modules can be supplied as either 25 Wor 100 W units,
depending
on the licence conditions, coverage required and the
reciprocity of the system. When calculating the radiated power from a
site,
the antenna gain, feed cable; combiner unit and filter losses should
be taken into account. Because of the insertionlosses through the
combining equipment, it is likely that 100 W units will be used in most
systems.
Other units include:
• Central Computer (CC)
Required to link together and control the various sites for multi-site
operation. Also provides connection to telephone services.
• Single-Site Interconnection Controller (SSIC)
For telephone interconnection on a single site network where there is
no CC available.
• PCMSwitch
Needed for routing the audio in multi-site and telephone interconnect
installations.
• Line Interface Unit (LIFU)
May be required between the channel shelf and the switch, to provide
line level matching, companding
and isolation.
SECTION TWO - LM REPEATER SITE SERVICE MANUAL

ff::\ INTRODUCTION
~--------------------
2.6 On-Site System Testing
On-site system testing is described in Sections 10 and 11.
Section 10 is for simplified on site testing and tests receiver SINAD,
transmitter output power and general operation. An HP 8920B test set
or similar is used for this test.
Section 11 is for full on site testing and is a more comprehensive test
including tests for output purity.
Normally
the tests in section 10 will be usedto commission a site but if
problems have been, or are likely to be encountered concerning sideband
emissions, noise, co-siting etc. the tests in section 11 should be
performed.
This test requires two signal generators and a spectrum
analyser. The
test can also be used in the workshop to check equipment
before putting it into the field.
SECTION TWO -LM REPEATER SITE SERVICE MANUAL 2-5

Q LINEAR MODULATION
~--------------------
3. Linear Modulation
. 3.1 Definition
Linear Modulation (LM) is a Radio Frequency (RF) transmission
technique suitable for the transfer of speech and high speed data over a
radio
bearer which is extremely narrow band. In this context narrow
band is a 5 kHz bandwidth radio channel.
The speech quality over a 5 kHz channel using LM techniques is
comparable to that achieved from a 12.5 kHz channel using Frequency
Modulation, and can be better under some circumstances. The available
bandwidth supports data transmission rates up to at least 14,400 bits
per second (V32bis). The system has good adjacent and co-channel
performance exceeding
that specified for narrow band systems both by
the DTI in the United Kingdom and the FCC in the United States.
Note also that for Linear Modulation systems, transmitted power is
related to the modulationlevel. This is unlike FM systems, which
transmit a constant envelope. This fact provides a lower power
consumption for
LM equipment when compared to AM or FM equipment
which is particularly important for the sizing of standby power systems
and for hand-portable units.
3.2 LM Methods
Linear Modulation uses a number of methods to achieve this high
quality performance. These are the use of a Transparent Tone In
Band ('rrIB) reference signal, Feed Forward Signal Regeneration
(FFSR) for signal recovery and Cartesian loop linearisation of the RF
transmitter.
3.2.1 TransparentTone In Band
A calibrated tone is inserted into the audio band. None of the wanted
audio is lost as a gap is specially created for it. The pilot tone is used in
the receiver to remove path distortions from the audio.
3.2.2 Feed Forward Signal Regeneration
In the receiver, FFSR is used to correct for Doppler shift and multipath
distortions which affect signals when transmitted in mobile
environments. The distortions on
the path are calculatedfrom the
received pilot tone, and the whole audio band is then corrected for these
distortions.
Tl'IB and FFSR together provide excellent resistance to mobile
distortion effects
and provide a transmission environment suited to
carryingvery
high quality speech and high speed data.
SECTION THREE -LM REPEATER SITE SERVICE MANUAL
3-1

LINEAR MODULATION Q
--------------------'~
3.2.3 Cartesian Loop
The Cartesian loop provides a linear transmitter which does not distort
the signal and minimises radiation into adjacent and near channels.
3.3 Transmission Process
3-2
The splitting process and the tone insertion occurs in a Digital Signal
Processor (DSP). The DSP can perform manipulations to the signal in
the digital domain which are not possible in the analog domain -for
example, the use of negative frequencies.
The audio signal from the microphone is first passed through an analog
to digital (A to D) converter and then input to the DSP. This digital
audio signal, which has an audio spectrum between 300 Hz and 3000 Hz,
undergoes TTIB processing. This splits the band at 1650 Hz to give an
upper and lower sub-band. The two sub-bands are then shifted apart
from each other in frequency to form a gap 600 Hz wide.
A pilot tone is inserted between between the two sub-bands. The
resulting audio signal is used to modulate the Cartesian Loop
transmitter .
Internally the DSP represents the audio signal not simply as the digital
stream derived from the A to D converter but as a complex quantity in
Cartesian form (e.g. the instantaneous value at any point in time is not
defined by amplitude and phase but by a Cartesian co-ordinate value
using 1 and Q axes, which represent the instantaneous amplitude and
phase).
The dynamic amplitude and phase of the RF signal
needs to be known
and controlled.
Definition
of a signal in terms of phase and
amplitude ispossible but it is easierto handle the
signals in terms
of a co-ordinate system, hence the
Cartesian or I and Q description.
This is made a practicalproposition
if the
manipulation is in the digital domain.
Figure 3-1
Q
Amplitude
Phase
It also takes the all positive 300 to 3000 Hz input audio signal, and
places it symmetrically about a nominal DC (0 Hz) point. The audio
range is now -1500 Hz to +1500 Hz.
The manipulation from the input audio signal to two audio sub-bands is
shown in Figure 3-2.
SECTION THREE - LM REPEATER SITE SERVICE MANUAL

Q LINEAR MODULATION
\J!!I,J-------
1 All Audio
.0 3000
Hz
I
DC
I
I
I
2 /
/ All audio
now in I and Q
DC
I
I
I
3 I
I
Lower:Sub-Band in I & Q
Upper Sub-Band
in I & Q
DC
Figure 3-2 Frequency Shift BasebandAudio to give Signal in I and Q and
Split into Upper and LowerSub-bands
Havingplaced the audio signal around a defined point (0 Hz), the DSP
now splits the negative portion away from the positive portion as two
sub-bands, the lower sub-band holding
the information derived from the
microphone in the 0 (actually 300) Hz to 1650 Hz spectrum the upper
sub-band containing the remaining 1650 Hz to 3000 Hz information.
The two sub-bands
are then 'moved apart' leaving a 'gap' between the
upper and lower sub-bands (Figure 3-3).
4 o
- 1--
Lower Sub
Band in 1&0
1650
-I ---------11--
Upper Sub
Band in 1&0
Figure 3-3 Shift Sub -bands in Frequency to make Gap
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LINEAR MODULATION Q
-----~-~
The nsp inserts a DC component into the centre point of the gap, which
corresponds to the pilottone. (Figure 3--4).
5
o 1650 1650 3000
-1--
Lower Sub
Band in 1&0
Upper Sub
Band in I &Q
Figure 3-4 Recombine Sub-bands and Insert Pilot Tone in Gap
The pilot tone is never reconstructed as audio and is therefore inaudible
(transparent) to the user, hence the description: Transparent Tone In
Band (TIm).
Once this digital processing has been completed, the digital audio from
the nsp is fed through a digital to analog (D to A) converter into the
modulator. It is up-converted directly to the final radio frequency. The
process inverts the two sub-bands so that the upper audio band appears
in the lower RF sub-band and vice versa. (Figure 3-5).
6
RF
3000 1650 1650 0(300)
-f--
Lower Sub to
Band in I &Q
Upper Sub
Band in I &Q
Figure 3-5 Up-convert to RF to Give Transmitted Signal
The pilot tone is the result of a DC level on the input to the Cartesian
Loop being mixed with the local oscillator. The TTm tone therefore
coincides with the carrier frequency.
3.4 Cartesian Loop Linearisation of the Transmitter
3-4
To ensure that the transmitter is linear and that signals do not suffer
from a non-linear transposition from audio to RF, a linearisation
technique is applied to the transmitter. This is achieved by the use of a
Cartesian Loop Transmitter (CLT).
The Cartesian Loop Transmitter (CLT) uses an RF directional
coupler to provide a sample of the outgoing transmission. This is fed
back to an RF demodulator which produces two outputs in Cartesian
form -I and Q (hence Cartesian Loop feedback). These are compared
with the values of the I and Q inputs to the modulator and any variation
compensated for. This feedback regime produces a very linear RF
transmitter with high efficiency.
SECTION THREE - LM REPEATER SITE SERVICE MANUAL

Q LINEAR MODULATION
'J!!f,J--~----
3.5 Reception Process
Any transmitted signal, whatever the transmission technique, is
distortedby the radio path in terms of amplitude, frequency and phase
(Figure 3-6) by a number off actors including Doppler and multi-path
(Rayleigh fading) effects.
1
RF
3000 1650 1650 o
· 1----'
Lower Sub
Band in 1&0
Upper Sub
Band in I &0
Figure 3~ Received Signal with Path Distortions at RF
-In an LM transmission this distortion affects both the transmitted audio
and the pilot tone.
The receiver
is a conventional 2-stage superheterodyne receiver which
presents a version
of the received signal at an IF of 12.5 kHz to the DSP
via an A to D converter. The DSP mixes this signal down to I and Q
about DC. (Figure 3-7).
2 TTIB
o 1650 1650 3000
· 1----'
Lower Sub DC Upper Sub
Band in I& Q Band in I & 0
Figure 3-7 Received Signal inI and Qabout DC
The amplitude, frequency and phase distortion measured on the pilot
tone will be
substantially the same as that affecting the two audio sub-
bands
and that measuring the pilot distortion will be a good measure of
overall signal distortion.
This measurement of amplitude, frequency and phase distortion
information,
is achieved by a comparison against an 'ideal' answer
produced by the receiving DSP. The 'answer' to the comparison is then
usedto equalise the two sub-band signals to negate the introduced
distortion.
The pilottone
is then separated from the audio sub-bands (Figure 3-8).
The sub-band signals are then delayed whilst the distortion information
derived from the pilot tone is fed forward for processing.
SECTION THREE - LM REPEATER SITE SERVICE MANUAL 3-5

LINEAR MODULATION ~
----------'J!!J)
3-6
3 o 1650 1650 3000
·f---
LowerSub oc Upper Sub
Band in I & 0 Band in I & 0
OC
Figure 3-8 Extract Pilot Tone from ReceivedALldio
This ensures that the correction is applied in the correct time frame.
This
is known as Feed Forward Signal Regeneration (FFSR).
Once the audio has been corrected the rest of the nspprocesses are a
reverse
of the transmission techniques.
The audio,
which is still in two associated sub-bands (Figure 3-9) is split
into two
separate bands and via a two stage mixing process within the
nsp (Figure 3-10) reformed into a coherent audio signal, but still
symmetrically arranged around 0 Hz (Figure 3-11).
4
o 1650 1650 3000
·f---
LowerSub oc Upper Sub
Band in I& 0 Band in I& 0
Figure 3-9 FFSR Corrects Frequency, Amplitude and Phase
5 o
·f---
Lower Sub
Band in 1&0
1650
OC
·f-------+_
OC
180 Hz mix
3000
Upper Sub
Band in 1&0
Figure 3-10 Separate Upper and LowerSub·bands
6
All audio in I and 0
OC
Figure 3-11 Rejoin Sub· bands and Lock Together
SECTION THREE -LM REPEATER SITE SERVICE MANUAL

Q LINEAR MODULATION
~-------
The final process recovers the audio into the 'real world'. (Figure 3-12)
7 I All audio
o 3000 Hz
-f-----
DC
Figure 3-12 Frequency Shift back to Baseband
SECTION THREE - LM REPEATER SITE SERVICE MANUAL
3-7