DMC Stratex Networks DXR100 User manual

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Copyright © 2000 DMC Stratex Networks Incorporated.
All rights reserved. No part of this publication may be reproduced, transmitted, transcribed, stored in a retrieval system, or translated into
any language or computer language, in any form or by any means, electronic, magnetic, optical, chemical, manual or otherwise, without the
prior written permission of DMC Stratex Networks.
DISCLAIMER
DMC Stratex Networks makes no representation or warranties with respect to the contents hereof and specifically disclaims any implied
warranties or merchantability or fitness for any particular purpose. Further, DMC Stratex Networks reserves the right to revise this
publication and to make changes from time to time in the content hereof without obligation of DMC Stratex Networks to notify any person
or such revision or changes.
CE MARK
This equipment has been designed to meet the requirements of the European Electromagnetic Compatibility Directive 89/336/EEC
(currently amended by 92/31/EEC). Operation of the equipment is designed to provide reasonable protection against harmful interference in
its electromagnetic environment without introducing intolerable electromagnetic disturbances.
TRADEMARKS AND REGISTERED TRADEMARKS
The DXR name and logo is a registered Trademark of DMC Stratex Networks Incorporated.
Parts of the DXR product design are protected under Patent Cooperation Treaty Application No: PCT/NZ93/00046.
Microsoft Windowsis a registered trademark of Microsoft Corporation in the United States and other countries.
All other marks are the property of their respective owners.
Corporate Headquarters
Americas Headquarters
DMC Stratex Networks
170 Rose Orchard Way
San Jose, CA 95134
USA
Tel: [phone]
Fax: [phone]
Europe/Africa/Middle East Headquarters
DMC Stratex Networks
Siskin Drive
Middlemarch Business Park
Coventry CV3 4JA
United Kingdom
Tel: [phone]
Fax: [phone]
Asia Pacific Headquarters
DMC Stratex Networks
10 Ang Mo Kio Street 65
#03-13 Techpoint
Singapore 569059
Tel: [phone]
Fax: [phone]
Seattle Operations
DMC Stratex Networks
3325 South 116th Street
Seattle, Washington 98168
USA
Tel: [phone]
Fax: [phone]
Wellington Operations
DMC Stratex Networks
24 Bridge Street
Lower Hutt
New Zealand
Tel: [phone]
Fax: [phone]
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100TECH 5.0


Intended Use of Equipment
"The enclosed equipment is classified under the R&TTE Directive 99/5/EC as a class 2.8 radio (microwave fixed
link) product. Point-to-point radio relay equipment is intended to be used for interconnecting typically private
and public networks and for interconnecting mobile base stations back to the PSTN point of presence (POP). The
DXR 200 equipment operates in the fixed bands between 300MHz and 2.7GHz, and is available in capacities of
4x64kbps, 10x64kbps, 31x64kbps, and 62x64kbps.
For details of where the equipment is intended for use please refer to the Country matrix below. It should also be
noted that a licence to operate this apparatus is likely and the appropriate regulatory administration should be
contacted."
DMC Stratex Networks intends to market this equipment where a cross (X) is shown.
Please Note: The information contained in this document has been gathered from the relevant government
authorities.
Austria
Belgium
Denmark
Finland
France
Germany
Greece
Ireland
Italy
Netherlands
Luxembourg
Norway
Portugal
Spain
Sweden
Switzerland
UK
330-470MHz XX XXX XXXXXXX X
890-960MHz XX X X XXXXXXXXX
1350-1550MHz 1E1 XXXXXXXXXXXXXXXXX
2100-2300MHz XXXXXX XXXXXXXXX
2300-2500MHz XXX XXXXXXXX XXXX
2500-2700MHz 4E1

Table of Contents
2000 DMC STRATEX NETWORKS i
DXR 100 TECHNICAL MANUAL
ISSUE 5.0
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Changes to this Manual 1
Product Compatibility 1
Safety 1
Customer Support 2
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Introduction 3
How this Manual is Organized 3
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General 5
DXR100 Functionality 6
DXR100 Configurations 13
Physical Construction 18
Front Panel Connections and Indicators 24
RF Branching Networks 29
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Standard EOW 33
4-Wire EOW Adaptor 34
Data Service Channel (V.24/RS-232) 35
NMS Board 37
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General 40
Radio Section 42
Modem Section 46
Control Functions 49
Interface 50

Table of Contents
ii 2000 DMC STRATEX NETWORKS
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Power Supply 53
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General 54
Lightning Protection 54
Before you Begin 55
Installing the Terminal 58
Protected Terminal Maintenance 60
Installing the Antenna 61
G.703 Termination 62
Alarm Termination 63
Connecting the Standard EOW Option 63
4-wire EOW Adaptor Option 64
EOW G.703 64 kbps Co-directional Connection 68
Data Service Channel 69
DC Power Connection 72
NMS Board 74
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General 75
Regular Maintenance Interval 75
Logbook 75
DXR100 Maintenance Checks 76
Site Maintenance Guide 78
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Introduction 81
What is the DXR NET?81
Requirements 83
Preparing your PC to use DXR NET 84
Connecting your PC to the DXR 100 terminal 85
Using DXR NET 86
Using the Explorer Tree functions 86
Using the Configuration Workspace functions 92
Using the Commissioning Workspace Functions 109
Using the Maintenance Workspace Functions 118
Problems Using DXR NET 125
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General 126
Power Up 126
Antenna Alignment 126

Table of Contents
2000 DMC STRATEX NETWORKS iii
DXR 100 TECHNICAL MANUAL
ISSUE 5.0
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General 130
DXR100 130
DXR100 Protected 134
Software Diagnostics 139
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General 148
Equipment Required 148
Bit Error Rate (BER) Tests 148
Protection Switch Testing 154
Transmitter Performance Tests 156
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Radio Frequency 163
Digital 163
Transmitter 164
Receiver 164
Duplexer (standard) 165
Data Service Channel Option 165
Orderwire Option 166
4-wire EOW Adaptor Option 166
NMS Option 166
Protected Option 166
Environmental 167
DC Power Supply 167
Alarms 167
Mechanical 167
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General 168
Tuning the Low Band Side 169
Tuning the High Band Side 170
Adjustable End Coupling 171
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Protection Switch Interface 173
Radio Modem Unit 173
Duplexers 174
Software 174
Manuals 174

Table of Contents
iv 2000 DMC STRATEX NETWORKS
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Accessories 175
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G.703 Termination 176
Alarm Termination 176
Standard EOW Handset Connection 177
Connecting the 4-wire EOW Option 177
EOW G.703 64 kbps Co-directional Connection 177
Data Service Channel Connections 177
DC Power Connection 178

List of Figures
2000 DMC STRATEX NETWORKS v
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ISSUE 5.0
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Figure 1: Non-protected DXR100 5
Figure 2: Hitless Switch Truth Table 10
Figure 3: Hitless Switch Block Diagram 12
Figure 4: Non-protected DXR100 - System Block Diagram 13
Figure 5: Non-protected DXR100 - Module Block Diagram 14
Figure 6: Protected DXR100 - System Block Diagram 14
Figure 7: Protected DXR100 - Module Block Diagram 16
Figure 8: DXR100 Frequency Diversity Configuration - Common Antenna 17
Figure 9: DXR100 Space Diversity Configuration 18
Figure 10: Cross Section of Non-protected DXR100 19
Figure 11: Power Supply/Modem Logic Bottom View 20
Figure 12: Interface Logic PCB Bottom View 20
Figure 13: RF Deck Top View 21
Figure 14: Cross Section of RMU 23
Figure 15: Cross Section of PSI 23
Figure 16: Non-protected DXR100 Front Panel 24
Figure 17: Protected DXR100 - Connectors and Indicators 26
Figure 18: RF Branching Network – Standard Protected 30
Figure 19: RF Branching Network – Space Diversity 31
Figure 20: RF Branching Network – Frequency Diversity 32
Figure 21: NMS/EOW Port Connection 33
Figure 22: 4-wire EOW Adaptor Block Diagram 34
Figure 23: Data 1 Interface Oversampling Scheme 36
Figure 24: Data 1 Interface Block Diagram 36
Figure 25: Data 2 Interface Block Diagram 37
Figure 26: Craft tool communications paths, NMS not fitted 38
Figure 27: NMS communications paths with NMS board fitted 39
Figure 28: DXR100 Radio and Modem - Block Diagrams 41
Figure 29: Circulator, Performance Monitor and -20 dBc Output Details 45
Figure 30: Duplexer Module - Block Diagram 46
Figure 31: Typical BER Performance with/without FEC 47
Figure 32: 1 x E1 Interface Block Diagram 51
Figure 33: 2 x E1 Interface Block Diagram 51
Figure 34: 4 x E1 Interface Block Diagram 52
Figure 35: DXR100 - Minimum Lightning Protection Requirements 58
Figure 36: 4-wire EOW Adaptor – Connection to Handset Connector 65
Figure 37: 4-wire EOW Adaptor – Connection to Interface PCB 65
Figure 38: 4-wire EOW Adaptor – Connection to Call Button and AGC Test Point 66
Figure 39: DXR100 Orderwire Connection 69
Figure 40: Data Service Channel Option Board 72
Figure 41: DXR100 - DC Power Connector 73

List of Figures
vi 2000 DMC STRATEX NETWORKS
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Figure 42: DXR net GUI - typical display 82
Figure 43: Modem/RF Link Setup Page for a Protected Terminal 94
Figure 44: Thresholds Page 95
Figure 45: Action Table Page 99
Figure 46: Interface Setup Page with Interface Type Drop-down Menu 101
Figure 47: External Inputs/Outputs Page - Setting Up an Alarm 103
Figure 48: IP Address Table Window 106
Figure 49: Routing Table Window 107
Figure 50: Routing Table Page - Typical IP addresses 109
Figure 51: Alarms Page 112
Figure 52: Controls Page 116
Figure 53: Alarms page in maintenance workspace 119
Figure 54: Constellation Diagram 120
Figure 55: AGC Graph 121
Figure 56: Terminal Details Page 124
Figure 57: DXR100 Antenna Signal Lobes 127
Figure 58: DXR100 - Correct Antenna Alignment on Signal Main Lobe 127
Figure 59: Incorrect Antenna Alignment on Signal Side Lobe 128
Figure 60: Constellation Diagram (DQPSK) 143
Figure 61: Constellation Diagram (16 QAM) 144
Figure 62: Noisy Constellation Diagram (16 QAM) 144
Figure 63: Constellation Diagram (DQPSK) - Example 1 145
Figure 64: Constellation Diagram (16 QAM) - Example 2 145
Figure 65: Constellation Diagram (16 QAM) - Example 3 146
Figure 66: Equalization Graph - Typical Performance Example 147
Figure 67: BER Test Setup 149
Figure 68: Unfaded BER Test Setup for DXR100 Protected 149
Figure 69: Unfaded BER Test Setup for DXR100 150
Figure 70: Faded BER Test Setup for DXR100 Protected 152
Figure 71: Transmitter Switching Test Setup for DXR100 Protected 154
Figure 72: Hitless Receiver Switching Test Setup for DXR100 Protected 155
Figure 73: Transmitter Power Test Setup for DXR100 Protected 157
Figure 74: Transmitter Spurious Emissions Test Setup for DXR100 157
Figure 75: Transmitter Spurious Emissions Test Setup for DXR100 Protected 158
Figure 76: Transmitter Bandwidth and Frequency Test Setup for DXR100 160
Figure 77: Transmitter Bandwidth and Frequency Test Setup for DXR100 Protected 161
Figure 78: Duplexer Diagram 168
Figure 79: LB1 Dip 169
Figure 80: LB2 Dips 169
Figure 81: LB3 Curve 169
Figure 82: LB4 Curve 170
Figure 83: HB1 Dip 170
Figure 84: HB2 Dip 171
Figure 85: HB3 Curve 171
Figure 86: HB4 Curve 171

Preface
2000 DMC STRATEX NETWORKS 1
DXR 100 TECHNICAL MANUAL
ISSUE 5.0
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Because DMC Stratex Networks is constantly seeking to improve quality and performance,
specifications and configurations may be subject to change without notice. As periodic
changes are made to the information contained herein, DMC Stratex Networks will
incorporate these changes into any new versions of this manual as they are released.
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While every effort has been made to verify the operation of DXR100 with many different
communications products and networks, DMC Stratex Networks makes no claim of
compatibility between DXR100 and other vendors' equipment. It is assumed that users have
thoroughly evaluated the performance of DXR100 in the environment in which it is to be
used.
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Please observe the general safety precautions outlined in this section during all phases of
operation and service of DXR100. If you do not comply with these precautions or with
specific safety warnings contained elsewhere in this manual or on the product itself, you will
violate the standards of design, manufacture, and intended use of the product. DMC Stratex
Networks does not assume any liability for any failure to comply with these precautions.
To help you to easily recognise safety warnings or precautions contained in this manual they
are prefixed by the warning symbol shown above.
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The DXR100 chassis must be grounded. If a short circuit occurs, grounding will reduce the
risk of electrical shock by keeping the equipment at the same potential as a person touching it.
Do not remove the external covers unless you are authorised to service the equipment.
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The DXR100 chassis is designed to conduct any heat generated by the DXR100 internal
components to the outside environment. Therefore, it can become uncomfortably warm to

Preface
22000 DMC STRATEX NETWORKS
DXR 100 TECHNICAL MANUAL
ISSUE 5.0
touch during normal operation. You should be aware of this when working on or near the
chassis, and should also ensure that the chassis does not come into contact with material that
is not heat-resistant.
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When DXR100 is transmitting, the antenna emits intense RF energy, which may cause injury
to someone coming into contact with it. It is therefore dangerous to stand, or have any part of
your body in front of the antenna during transmissions.
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The transmitter module of DXR100 contains Beryllium Oxide ceramic. This substance is
completely safe while in solid form within the module but is highly toxic if inhaled or
absorbed by the skin in powder form. You should therefore be extremely careful when
handling the components to ensure that you do not chip, grind or damage them.
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Do not install or operate DXR100 in any environment where there are flammable gases or
fumes. To do so will create a significant safety hazard, which could expose you to the risk of
physical injury.
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Electrostatic discharge (ESD) can damage or destroy the sensitive electrical components
contained within DXR100. Therefore, you must always use full ESD precautions whenever
the external covers of DXR100 are removed.
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Do not install parts, substitute parts or perform any unauthorised modification to DXR100. If
repair is required you should return the product to your DMC Stratex Networks representative
or directly to DMC Stratex Networks to ensure that safety features are maintained.
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If after reading this manual you experience any difficulty installing or using DXR100, you
should first contact your local DMC Stratex Networks representative or alternatively contact
DMC Stratex Networks directly. Contact details are as follows:
DMC Stratex Networks
24 Bridge Street
Lower Hutt
Wellington
NEW ZEALAND
Attention: Customer Services Department
Telephone: [phone] or
[phone]
Facsimile: [phone]
E-mail General: [e-mail]
E-mail RMA: [e-mail]
E-mail Product Support: [e-mail]
E-mail Software Support: [e-mail]

About this Manual
2000 DMC STRATEX NETWORKS 3
DXR 100 TECHNICAL MANUAL
ISSUE 5.0
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The purpose of this manual is to provide the technical information necessary to allow you to
install, commission and maintain the DXR100 Digital Microwave Radio System. It contains
basic technical descriptions at module and system level. The information in this manual is for
trained technicians and/or engineers. It does not provide information or instruction on basic
technical procedures.
We recommend that you read the relevant sections of this manual thoroughly before
beginning any installation or operational procedures on DXR100.
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This section gives an outline of the content and aim of the manual, and also provides
instructions on how to use it.
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This section contains descriptions of the standard hardware associated with DXR100. It
contains functional descriptions as well as technical and physical specifications
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This section contains descriptions of the optional equipment that can be supplied with
DXR100. It contains functional descriptions as well as technical and physical specifications.
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This section contains detailed descriptions of DXR functionality including block diagrams of
each of the DXR100 sections.
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This section contains step-by-step procedures for installing and commissioning DXR100. It
tells you what tools and equipment you will need as well as power and antenna requirements.
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This section contains advice on how to carry out maintenance on the DXR100.

About this Manual
42000 DMC STRATEX NETWORKS
DXR 100 TECHNICAL MANUAL
ISSUE 5.0
5GEVKQP&:40 6
This section provides the information needed to install DXR NET on your PC hard drive, and
how to use it to carry out simple checks and modifications to the setup of a DXR 100 link.
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This section contains the information necessary to allow you to commission DXR100 after
installation and includes details of antenna alignment procedure.
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This section contains step-by-step procedures to allow you to identify and trace faults on
DXR100 as well as take action to correct the fault.
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This section contains step-by-step procedures for DXR100 and desired results for optimum
performance.
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This section provides you with the technical and physical specifications of the DXR100,
associated interfaces and options.
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The appendices contain information that relates to the content of this manual but is not
appropriate for the main body of the document. It includes the following:
•Duplexer Alignment
•Abbreviations
•Parts List
•Cable Pin-out Information

Overview
2000 DMC STRATEX NETWORKS 5
DXR 100 TECHNICAL MANUAL
ISSUE 5.0
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DXR100 is a point-to-point digital microwave radio system designed primarily for medium to
long haul, thin route telecommunications networks. It comprises a digital radio packaged in a
standard 19-inch 3U horizontal rack shelf or 120 mm slim rack.
The DXR100 is available in three configurations:
•Non-protected - single DXR100 terminal
•Protected - two DXR100 Radio Modem Units (RMUs) with a Protection Switch Interface
(PSI)
•Upgradeable -as for Protected, but with only one DXR100 RMU
Figure 1: Non-protected DXR100

Overview
62000 DMC STRATEX NETWORKS
DXR 100 TECHNICAL MANUAL
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DXR100 is designed to operate in the following frequency bands and capacities:
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330-470 MHz 2000-2300 MHz 1 x E1 1 x 2 Mbps
890-960 MHz 2300-2500 MHz 2 x E1 2 x 2 Mbps
1350-1550 MHz 2500-2700 MHz 4 x E1 4 x 2 Mbps
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The main DXR100 functions can be classed under the following main headings:
•Digital Interface (all DXR100 configurations)
•Modem and Radio (all DXR100 configurations)
•Transmit Switching (protected DXR100 only)
•Tx Switch Oscillation Protection (protected DXR100 only)
•Receive Switching (protected DXR100 only)
All DXR100 configurations use advanced digital signal processing techniques and powerful
low overhead forward error correction (FEC) to support a range of data rates with excellent
spectrum efficiency. Reed-Solomon FEC code corrects up to 10 errors per 204-byte block,
virtually eliminating noise and residual bit error rate problems often experienced in urban low
frequency microwave systems. A 16 tap transversal equalizer is included to reduce the effects
of multipath interference.
Protected versions of the DXR100 offer redundancy on the transmitter and receiver sections,
including the modem. Should a failure occur in any of these sections, the redundant
transmitter or receiver is switched on line. Transmit and receive switching is done
independently. Manual mode may be selected to allow one RMU to be replaced while
maintaining normal operation via the other.
Switching on receive is fully automatic and is based on detection of un-correctable errors by
the forward error correction (FEC) circuit. Receive hitless switching (i.e., the switching
causes no errors in receiver output), allows for errorless receiver diversity operation.
The protected DXR100 can be configured to switch from the main to the stand-by transmitter
by selecting any one of the following alarm conditions:
•Low Transmitter Forward Power
•Temperature too high
•LO oscillator out of lock
•Major Alarm (triggered by failure of any sub-module)
•Manual switch-over commands for testing and maintenance

Overview
2000 DMC STRATEX NETWORKS 7
DXR 100 TECHNICAL MANUAL
ISSUE 5.0
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The digital interface combines the E1 inputs and complies with the ITU-T Recommendation
G.703. Standard E1 interface connections are 120 ohm balanced, accessed via the front panel
DB-25 connector. If some ports require 75 ohm connections external 120 ohm to 75 ohm
balun transformers may be used. If all ports require 75 ohm connections, all radio E1
interfaces may be set to 75 ohm operation via a software change.
Note: Although a software change can set E1 output interfaces from 120 to 75 ohm (and
vice versa), the E1 input impedance remains at 120 ohm. To prevent matching
problems, all 75 ohm accessory cables for the DXR100 are fitted with matching
resistors to obtain a 75 ohm input.
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The modem combines the E1 inputs and appends the FEC parity bytes. DQPSK, or 16 QAM
modulation is applied and the signal is sent to the transmitter for up-conversion to the
appropriate microwave frequency and higher power. The radio signal is sent to the antenna
via a duplexer.
The radio signal is received at the remote terminal where it is down converted and processed
by the 16 tap transversal equalizer to compensate for multipath interference.
After demodulation any errored bytes are corrected using the Reed-Solomon FEC algorithm.
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Switching between transmitters in a protected DXR100 can be either alarm driven, or on
command from the user. When alarm driven, it will normally only occur in the event of a
transmitter failure that causes an alarm to become active, or a RMU failure that makes the
RMU incapable of communicating to the PSI. If there are no faults there will be no transmit
switching, unless the manually commanded by the user (eg, during testing the transmit
switching, or selecting a “prefered”transmitter).
In order of decreasing priority, the conditions that govern transmitter switching are:
•Tx Manual forcing mode
•RMU not communicating with PSI
•Configured alarms being active
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The user selects the on-line transmitter using the DXRtech menu. They would usually do this
either to check that the protection switching function is working properly, or to switch to a
“prefered”transmitter.
Note: If the user uses the Tx manual forcing mode to select a transmitter, then the selected
transmitter will be made on-line whether or not it has alarms.

Overview
82000 DMC STRATEX NETWORKS
DXR 100 TECHNICAL MANUAL
ISSUE 5.0
4/70QV%QOOWPKECVKPIYKVJ25+
If a RMU has a total failure such that it can not communicate with the PSI (eg. the RMU is
powered off, or removed altogether), then the PSI will switch to the transmitter in the other
RMU, provided that this RMU is successfully communicating with the PSI.
Note: If neither RMU can communicate with the PSI, then no switching will take place
and there will be a “Cannot Switch”alarm on the PSI together with a red OK LED
on the PSI front panel.
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The alarms that cause transmit switching are configurable and normally include the following:
•Internal Supply Voltage out of limits (5V Analog, 5V Digital, 10V, Tx PA Bias)
•Transmit PLL Unlocked
•Tx Forward Power out of limits
In some applications, such as Warm Standby, the following alarms can also be used:
•Tx Reverse Power out of limits
•Temperature
Note: If both RMUs have an alarm active that would normally cause a transmit switch,
there will be no switching. There will also be a "Cannot Switch" alarm on the PSI
together with a red OK LED on the PSI front panel.
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Some unusual circumstances may cause the Protection Switching function to oscillate
between the two transmitters. This happens when both transmitters have a condition where
they have a switch causing alarm only when on-line. If that happens, a PSI will switch back
and forwards between the two transmitters. This rapid repetitive switching can be a serious
situation if uncontrolled, as Tx relay operation causes error bursts that affect the useability of
the link. An example of a fault that could cause switch oscillation is an antenna fault causing
high return loss, when using a DXR100 that is configured to switch on a Reverse Power
Alarm. This can become an oscillation condition because the reverse power alarm is
suppressed on the off-line Tx.
The DXR100 includes protection against this situation by dynamically slowing the Tx
switching rate, so the link (assuming it is still operational) may continue to operate with
minimum impact caused by Tx switching induced error bursts, while still maintaining the
ability to switch quickly in the event of an isolated alarm.
There are two internal registers that control the behaviour under oscillation conditions. The
registers are the Guard Timer, and the Guard Time. The Guard Timer is activated by any
condition causing a Tx switch, and remains active for the period defined by the Guard Time.

Overview
2000 DMC STRATEX NETWORKS 9
DXR 100 TECHNICAL MANUAL
ISSUE 5.0
Note: Take care not to confuse the names of the two registers.
Initially, if a condition that would cause the PSI to switch transmitters arises, the PSI will
respond immediately. However, when a switch has occurred the PSI will activate the Guard
Timer. It then waits for the interval defined in the Guard Time register before it responds to
any future condition that would cause it to switch back to the original transmitter.
Note: The guard time is 5 seconds under initial or static conditions.
The guard time is dynamic. If there is another switch causing condition present when an
initial Guard Timer expires, then the PSI will switch again and the guard time will then be
doubled. The Guard Timer activation from this second switch causing condition will run for
the period set by the new Guard Time. If there is another switch causing condition when the
second Guard Timer expires, then the PSI will switch again, the guard time will double again,
and the Guard Timer will run for this new guard time period.
Therefore, when the conditions for switch oscillation exist:
•The first switch will happen immediately the conditions for switch oscillation arise.
•The second switch will occur after 5 seconds.
•The third switch will happen after 10 seconds.
•The fourth switch will happen after 20 seconds, etc.
In addition to the above behaviour, every 60 seconds the guard time will be halved. This will
happen until the guard time returns to its rest value of 5 seconds. This guard time decay
allows the DXR100 to automatically recover, should the conditions for switch oscillation
disappear, to its normal state allowing the most rapid transmitter switching response. It also
effectively limits the guard time to 80 seconds, as at that point the guard time will decay faster
than it can be doubled.
It would appear that the situation where the oscillation condition disappears leaving a high
guard time value may cause a protected DXR100 to be unable to switch for a long time.
However, that is not the case. The DXR100 will be ready to switch as soon as the current
guard timer expires. On average, this will be half the guard time value at the instant the
switch oscillation condition disappears. Although the time taken for the guard time to decay
back to five seconds could be nearly five minutes, this will not affect the ability of the
DXR100 to switch immediately. Should the oscillation condition subsequently reappear
before the guard time has decayed back to 5 seconds, the first switch will be instant, but the
next switch will be delayed by the value of the guard time at the time of the switch?
The end result is a self limiting, self-decaying, exponential backoff of transmitter switching in
the event of an oscillation condition.
Note: The guard time can be manually reset to five seconds using DXRtech, allowing
instant recovery to the normal state when required. This is most useful when doing
switching testing on the bench.

Overview
10 2000 DMC STRATEX NETWORKS
DXR 100 TECHNICAL MANUAL
ISSUE 5.0
4GEGKXG5YKVEJKPIRTQVGEVGF&:4QPN[
Receive switching may arise from a receiver failure, or from the degradation of the received
signal in one receiver but not the other (eg. as would happen in a diversity system). As a
result of the second condition, the DXR100 uses hitless receive switching (i.e. receive
switching that does not cause errors in the received data stream).
The DXR100 offers an errorless, hitless switch that offers standards of performance
unimaginable with traditional hitless switching technology.
The hitless switch in the DXR100 is driven by the FEC in the receivers. The receiver
switching is signal quality driven and not alarm driven. The receiver only needs to deliver a
good output, and if it is able to do that even in the presence of a fault, then its output is good
enough to be used.
The quality of the receiver output is monitored by the FEC in each receiver, which processes
received data in blocks of 1632 bits. The quality criterion for receive switching is very simple
- the receiver output signal (from the FEC) is good if the block of FEC output data is 100%
error free, and not good if it is not. Even one error on the FEC output of one receiver is
sufficient to initiate a receive switch, provided that the FEC in the other receiver can confirm
its block is 100% error free. What is more, since the result (success or failure) of the FEC in
each receiver to correct all errors is known before the data is output from the FEC, then the
hitless switch will select the good receiver before the block containing errored data reaches
the PSI. The result of this is that the customer interface will be error free, despite the on-line
receiver having errors and the receivers being switched.
The other major benefit of the FEC driven hitless switch is that there is no need to consider
the timing differences caused by different feeder lengths between main and diversity antennas
in a space diversity system. The buffers associated with debursting the FEC are also used to
remove timing differences by synchronizing the two receiver outputs exactly, and the timing
differences that can be tolerated by the FEC buffers far exceed what could be caused by any
practical feeder length difference. For example, in a 4xE1 radio, the timing difference that
can be tolerated is up to ±187µs, corresponding to a feeder length difference (for feeder
velocity factor of 0.8) in excess of 44km.
Figure 2 shows the truth table for the hitless switch.
('% +PRWV $'4 ('% 1WVRWV $'4 #EVKXG 1WVRWV 1WVRWV $'4
#$#$
Ignored Ignored =0 =0 A or B =0
Ignored Ignored >0 =0 B =0
Ignored Ignored =0 >0 A =0
Ignored Ignored >0 >0 A or B >0
Figure 2: Hitless Switch Truth Table
The error evaluation and switching decision is made once per 1632 bit block from the FEC. In
a 4xE1 DXR100, there is 5333 blocks per second, meaning the receiver switching will be
performed at up to 5333 times per second.

Overview
2000 DMC STRATEX NETWORKS 11
DXR 100 TECHNICAL MANUAL
ISSUE 5.0
An important feature of the above table is that the raw receiver BER, going into the FEC, is
unimportant. As long as all errors are corrected, then there is no difference between a
receiver whose raw output is error free and one whose raw output has some correctable errors.
In both cases the FEC outputs will be exactly the same error free data and both would be
equally suitable for delivery to the customer.
The only situation when the hitless switch output will contain errors is when the FEC of
neither receiver can correct a heavily errored block. However, for this to happen, both
receiver FEC outputs would be unusable anyway, and the complete protected DXR100 would
be considered to have faded. For the FEC to fail there would need to be a raw receiver BER of
around 5x 10-3. Because the FEC cannot correct ANY errors in an uncorrectable block, this
BER would also be seen on the FEC Output. There is no relative evaluation made of quality
if both receivers have uncorrectable errors present - whichever receiver output is used, the
BER is too high to for the output to be useful. In this case the hitless switch will remain on
the last receiver to output a good block, which will most likely be the better of the two.