IEEE Guide for Microwave Communications System Development: Design, Procurement, Construction, Maintenance, and Operation

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The Institute of Electrical and Electronics Engineers, Inc.

345 East 47th Street, New York, NY 10017-2394, USA

ISBN 0-7381-0188-5

No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher.

IEEE Std 1404-1998

IEEE Guide for Microwave Communications System Development: Design,

Procurement, Construction, Maintenance, and Operation

Sponsor

Intelligent Transportation Systems of the

IEEE Standards Coordinating Committee 32

Approved 13 April 1998 IEEE-SA Standards Board

Abstract: The needs and requirements specific to the design, procurement, construction, maintenance, and operation of a microwave system are addressed. Steps for a variety of applications have been included in this guide; however, users should select only those steps that apply to their particular system(s) and their procurement policies.

Keywords: communications infrastructure, digital microwave, loop system, microwave spurs, ring system, star system, teleconferencing, terrestrial microwave system

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Introduction

(This introduction is not part of IEEE Std 1404-1998, IEEE Guide for Microwave Communications System Develop- ment: Design, Procurement, Construction, Maintenance, and Operation.)

The Intelligent Transportation Society of America (ITS America) was organized to support the development of US Department of Transportation (USDOT) Intelligent Transportation Systems (ITS) and subsequently requested standards assistance from the IEEE. The Þrst meeting of the IEEE Standards Coordinating Com- mittee on Intelligent Transportation Systems (SCC32) was convened by John E. May at Newport Beach, California on 22 May 1992.

Traditional DOT electronic system construction and maintenance projects have been limited in scope to ÒlocalÓ systems and system control environments that do not require system-to-system communications.

Each system has usually been a stand-alone system, and in many cases, proprietary design has negated the ability to communicate with an adjacent system(s). These electronic systems are relatively new to the DOT environment and most are trafÞc control systems. However, after the US Legislature passed the Intermodal Surface Transportation EfÞciency Act of 1991 (ISTEA), the need to communicate with many discrete trafÞc management systems over a large geographic area became essential if the concept of ITS was to become a reality. The key to cost-effective ITS systems is a cost-effective, highly reliable communications infrastructure. A terrestrial microwave system can be designed to meet these requirements.

This guide is the product of an SCC32 Working Group responsible for the development of a document that would provide guidance to the USDOT, as well as state and local transportation departments in developing a terrestrial microwave system, including the steps required for design, procurement, construction, maintenance, and operation.

At the time this guide was completed, the Working Group on Microwave Communications System Develop- ment: Design, Procurement, Construction, Maintenance, and Operation had the following members:

Robert L. Gottschalk,Chair

The following persons were on the balloting committee:

Thomas G. Brooks, Jr.

Lawrence R. Danello

Gene A. Glotzbach John M. Hogan Clinton L. Hugghins

Gerald M. Kessler Terry A. Posey

John H. Bailey Robert Barrett Roger R. Block Gene A. Buzzi James Costantino Lawrence R. Danello Spiros Dimolitsas

John R. DiSalvo Samuel F. Gargaro Arthur H. Greenberg James E. Gunn Gerald M. Kessler Richard Laine Craig E. Lekutis

Roger D. Madden John E. May Alan Otwell Leonard L. Tripp Joseph Ulaszek Charles E. Wallace Richard Weiland

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The Þnal conditions for approval of this guide were met on 13 April 1998. This guide was conditionally approved by the IEEE-SA Standards Board on 19 March 1998, with the following membership:

Richard J. Holleman, Chair Donald N. Heirman,Vice Chair Judith Gorman,Secretary

*Member Emeritus

Catherine K.N. Berger IEEE Standards Project Editor

National Electrical Code and NEC are registered trademarks of the National Fire Protection Association.

Satish K. Aggarwal Clyde R. Camp James T. Carlo Gary R. Engmann Harold E. Epstein Jay Forster*

Thomas F. Garrity Ruben D. Garzon

James H. Gurney Jim D. Isaak Lowell G. Johnson Robert Kennelly E. G. ÒAlÓ Kiener Joseph L. KoepÞnger*

Stephen R. Lambert Jim Logothetis Donald C. Loughry

L. Bruce McClung Louis-Fran•ois Pau Ronald C. Petersen Gerald H. Peterson John B. Posey Gary S. Robinson Hans E. Weinrich Donald W. Zipse

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IEEE Guide for Microwave Communications System Development: Design,

Procurement, Construction, Maintenance, and Operation

1. Overview

This document provides step-by-step guidance to individuals involved in the development of terrestrial microwave communications systems. Included are the requirements for the design, procurement, construction, maintenance, operation, and test of such systems.

1.1 Scope

This guide was developed in accordance with traditional microwave system development methods. This guide addresses the needs and requirements speciÞc to the design, procurement, construction, maintenance, and operation of a microwave system. Steps for a variety of applications have been included in this guide;

however, readers should select only those steps that apply to their particular system(s) and their procurement policies.

It is recommended that this guide be thoroughly reviewed and all steps not applicable to the needs of the user and/or project be deleted. The customized guide should then be used as a project-speciÞc guide. Each step in the modiÞed guide can then be used as a check-off item to ensure that all the requirements of the process have been fulÞlled or completed.

1.2 Purpose

The purpose of this document is to provide a step-by-step guide for the development of a microwave communications system for the non-technical manager or purchasing agent or to serve as a handy checklist for the experienced communications engineer/technical manager.

This guide addresses the basic issues associated with each potential element of a microwave communications infrastructure construction project. It was the intent of the writers to provide a generic and basic

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approach, addressing as many of the possible project elements, rather than provide a more detailed document that would be typical of a procedure or speciÞcation. This document is a guide and should not be used as the only source of information when designing, procuring, constructing, maintaining, and operating a microwave communications system.

The guide can be used by both the communications engineering professional who may wish to review one or more elements of microwave project design and by the non-technical manager/purchasing agent who desires to become familiar with the various aspects of microwave system project development.

2. References

This guide shall be used in conjunction with the following publications. If the following publications are superseded by an approved revision, the revision shall apply.

ANSI/EIA 195-C-1985, Electrical and Mechanical Characteristics for Terrestrial Microwave Relay System Antennas and Passive Reßectors.¹

ANSI/EIA 310-D-1992, Racks, Panels, and Associated Equipment.

ANSI/EIA/TIA 222-E-1991, Structural Standards for Steel Antenna Towers and Antenna Supporting Structures.

ANSI/NFPA 780-1997, Lightning Protection Code.²

ASCE 7-95 Minimum Design Loads for Buildings and Other Structures.³ EIA-252-A-1972, Standard Microwave Transmission Systems.⁴

EIA-368-1969, Frequency Division Multiplex Equipment Standard for Nominal 4 kHz Channel Bandwidths (Non-Compandored) and Wideband Channels (Greater than 4 kHz).

IEEE Std C62.41-1991 (Reaff 1995), IEEE Recommended Practice for Surge Voltages in Low-Voltage AC Power Circuits.⁵

NFPA 70-1996, National Electrical Code^¨ (NEC^¨).⁶ UL-752-1995, Bullet-Resisting Equipment.⁷

1ANSI/EIA publications are available from Global Engineering, 1990 M Street NW, Suite 400, Washington, DC, 20036, USA. They are also available from the Sales Department, American National Standards Institute, 11 West 42nd Street, 13th Floor, New York, NY 10036, USA.

2NFPA publications are available from Publications Sales, National Fire Protection Association, 1 Batterymarch Park, P.O. Box 9101, Quincy, MA 02269-9101, USA.

3ASCE publications are available from American Society of Civil Engineers, 1015 15th Street NW, Suite 600, Washington DC 20005 USA.

4EIA publications are available from Global Engineering, 1990 M Street NW, Suite 400, Washington, DC, 20036, USA.

5IEEE publications are available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, P.O. Box 1331, Piscataway, NJ 08855-1331, USA.

6The National Electrical Code is available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, P.O. Box 1331, Piscataway, NJ 08855-1331, USA. It is also available from Publications Sales, National Fire Protection Association, 1 Batterymarch Park, P.O. Box 9101, Quincy, MA 02269-9101, USA.

7UL standards are available from Global Engineering, 1990 M Street NW, Suite 400, Washington, DC, 20036, USA.

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IEEE DESIGN, PROCUREMENT, CONSTRUCTION, MAINTENANCE, AND OPERATION Std 1404-1998

3. Acronyms

AASHTO American Association of State Highway and Transportation OfÞcials

AGL Above Ground Level

ANSI American National Standards Institute EPA Environmental Protection Agency ERP Effective Radiated Power

FAA Federal Aviation Administration FCC Federal Communications Commission FHWA Federal Highway Administration HVAC Heating, Ventilation, Air-conditioning

IEEE Institute of Electrical and Electronics Engineers I/O Input/Output

ISO International Organization for Standardization

ISTEA Intermodal Surface Transportation EfÞciency Act (1991)

ITS Intelligent Transportation System [formerly Intelligent Vehicle Highway System (IVHS)]

ITS America Intelligent Transportation Society of America [formerly the Intelligent Vehicle Highway Society (IVHS) of America]

ITU-R International Telecommunications UnionÐRadio Communications Sector

ITU-T International Telecommunications UnionÐTelecommunications Standardization Sector IVHS Intelligent Vehicle Highway System [replaced by Intelligent Transportation System (ITS)]

LP LiqueÞed Petroleum

NEC National Electrical Code

NEMA National Electrical Manufacturers Association NFPA National Fire Protection Association

NRTL Nationally Recognized Testing Laboratory

NTIA National Telecommunications and Information Agency NTP Notice to Proceed

PCS Personal Communications Service

RF Radio Frequency

RFB Request for Bid RFI Request for Information RFP Request for Proposal UL Underwriters Laboratories UPS Uninterruptible Power System USGS US Geological Survey VSWR Voltage Standing Wave Ratio

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4. Professional assistance requirements

Professional assistance may be required for two speciÞc reasonsÑÞrst, to fulÞll the need for technical assistance not available within the user organization, and second, to satisfy professional engineer licensing or cer- tiÞcation required by either policy or law. In either case, the professional engineer, whether a qualiÞed registered professional engineer or a communications engineer, should bring a level of expertise to the process that is both cost effective and time effective.

5. Assignment of responsibility

It is important to assign responsibility as early in the process as possible. Agencies in the public sector usually have policies, procedures, and laws governing the process for the assignment of authority and responsibility to programs addressed by this guide, whereas private sector planners may not have any predeÞned rules or policies. Therefore, the initial project activities, which include mission statements, budget issues, and work scopes, should clearly identify where the program authority and responsibility lies. It is important that technical and complex projects (e.g., microwave communications systems) be controlled by managers or engineers who are qualiÞed communications specialists. Individuals or groups who do not practice communications engineering are not qualiÞed and should not be considered.

5.1 Engineering

The individual or group selected to be responsible for the engineering design, maintenance, and operation of a microwave system should be a qualiÞed communications engineer or communications engineering group.

The individual or group should be a specialist or specialize in this area of electrical engineering. If qualiÞed personnel are not internally available, engineering assistance should be acquired from an outside source.

5.2 Procurement

The procurement policies affecting each project should be considered in the design process. In addition, institutional standards should be considered and possibly changed or waived for some communications projects. It is best to identify any impediments in advance and obtain permits, license waivers, or design modiÞcations before making a Þnal commitment to the proposed project.

Failure to address institutional issues early in the conceptual and design phases can delay the project later on and almost always increases the Þnal and/or long-term recurring costs of the project. Responsible engineering and management are necessary to prevent delays and minimize costs.

Given the policies and standards, it is necessary to establish the procurement methodology that is appropriate to the project. The owner may choose among competitive procurement [bid or request for proposal (RFP)], negotiated sole-source procurement, or operating lease.

5.3 Implementation

Implementation of a microwave communications system is an intensive technical effort. For most projects, successful implementation requires a dedicated project manager. This individual oversees activities such as scheduling, site acquisition and development, permitting, vendor/contractor coordination, receiving, inven- tory and storage of equipment and materials, construction supervision, Federal Aviation Administration (FAA) and Federal Communications Commission (FCC) compliance, system optimization, and performance veriÞcation. Time should be allocated for extensive Þeld travel and regular progress meetings with the system vendor.

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5.4 Operation

Operational issues include system management, site management, maintenance, and other issues associated with ofÞce management. System management includes resource allocation, maintenance strategies, and future growth requirements. Site management includes tower management, frequency and channel selection, and loading. Maintenance funding and resource allocation may be a shared responsibility between opera- tions and maintenance. Other management issues are essentially ofÞce management requirements that should be deÞned and allocated budget funds.

NOTEÑTower management includes tower/site use agreements with other users.

5.5 Maintenance

Maintenance should be considered from the beginning of the project and effectively begins during system burn-in and should continue throughout the life of the system. Maintenance tactics, billing, training, network monitoring and control, response time, equipment and vehicle requirements, and preventive maintenance schedules are all directly associated with maintenance and indirectly associated with operation.

Two basic maintenance concepts are contract and in-house maintenance. Contract maintenance is performed by independent contractors who perform speciÞc maintenance tasks delineated by a contractual agreement between the microwave system owner and the maintenance contractor(s). In-house maintenance is maintenance performed by personnel employed directly by the microwave system owner.

The development of maintenance capabilities (e.g., acquiring personnel, equipment, spare parts, and training) should be done sufÞciently in advance so that the maintenance personnel will be ready to assume maintenance responsibility upon initial system start-up.

5.6 Legal

Legal issues will vary from project to project. It is recommended that site selection be considered a part of the initial design engineering and all FAA, FCC, Federal Highway Administration (FHWA), and local building and zoning permit approvals be obtained before advertising for bids. Unless all approvals are guaranteed, a project may be delayed or completion may be prevented due to a rejection by any one authority such as those delineated herein.

However, it should be recognized that large systems will present a logistical problem to the manager who attempts to obtain all licenses and permits prior to advertising for bids. FCC licenses will usually expire between the time of the bid and the completion of construction, maybe more than once. FAA studies also expire if the FCC license is not issued promptly. Therefore, large system planning should also include the legal issues associated with the logistical necessity of awarding a contract Þrst and requiring the contractor to complete the FCC licensing before the construction notice to proceed (NTP) can be authorized. In all cases, the contract should have a cancellation clause, without penalty to the buyer, in the event that the FCC does not grant a license(s) for the system.

6. Design requirements

The design requirements of a terrestrial microwave system are directly driven by the needs of the owner(s) and user(s) and should be determined during the user needs assessment. Design requirements are affected by the volume and density of information that needs to be transported, the terrestrial characteristics of the area of operation, and geographic restrictions for the site locations.

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System design is an application engineering iterative process where the communications engineer strives to combine the needs of the user(s) with available technology, regulatory limitations, and budgetary constraints.

6.1 User needs assessment

Assessing the needs of the user is the major element that deÞnes the design of the system. The assessment should include both the current and the estimated future system requirements (e.g., voice, data, and video applications) that will be accommodated, as well as the system volume, density, security, and alarm network preferences.

6.1.1 Mainline (backbone) design

A typical microwave communications system is usually the long-distance carrier of intelligence (communications infrastructure) from smaller communications elements or networks that cannot independently transport the needed information the required distance to the desired locations in a cost-effective manner.

The mainline, or backbone element, of the microwave system is designed to perform continuously with near- zero outages for the life of the system. Design geometry can be either in the form of a system loop where the beginning site and the end site are linked together by microwave, or the spacial requirements could manifest a continuous-line geometry where a number of sites are connected together such that the Þrst and the last site are too far apart to be linked together.

Both mainline designs may also include elements called system spurs, which bring information from important nodes directly to the mainline system via microwave. A system comprised only of spurs is called a ÒstarÓ system.

6.1.2 Microwave spurs

The microwave spur is a subset of the mainline system. The spur is usually required when an important information node is inconveniently located for mainline routing or when the number of channels is insufÞ- cient to justify the cost of the large capacity of mainline equipment, yet less expensive than the recurring costs of leased utility services.

Spurs connect important nodes to the mainline and may be limited in capacity and performance.

6.1.3 Loop (ring) design

When the system geometry is such that the sites can be connected together into a continuous loop, then reliability through redundancy becomes a channel capacity function rather than an equipment conÞguration issue. In addition, reliability could be further improved by using a two-loop conÞguration with a common segment at its center.

If the channel capacity of each path is equal, then the channel direction becomes bidirectional and the loss of one site only affects the information input/output (I/O) from that site. Information that normally travels in one direction to an output point can travel in the opposite direction and access the same output point even when one site between the two points has failed.

Loop design may require more channels in some paths; however, the cost of complete redundancy (hot standby) is usually much greater than a one-to-one corresponding channel plan using a loop (ring) closure design.

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6.1.4 Availability and performance/reliability

System performance (e.g., path reliability and message circuit quality) is determined from the user needs assessment. The communications engineer designs the system/equipment conÞguration that results in the optimum system availability and performance. A combination of design factors (e.g., operating environment, technical operating parameters, equipment redundancy, space diversity, route diversity, and frequency diversity) have to be considered and are routinely addressed by the design engineer.

6.1.4.1 Operating environment

The geographic area of operation will have a direct effect on microwave signal propagation between sites.

The density of the atmosphere and the nature of daily and seasonal changes are important design considerations. Path engineering will be different for arid and humid climates. Similarly, engineering for a path that runs over smooth terrain or water will heighten the concern for propagation reliability as opposed to a path that traverses irregular or rugged terrain. Additional considerations are rainfall rates, obstructions in or near the path, and the presence of foliage and its type and expected growth.

6.1.4.2 Technical operating parameters

The performance objectives, path length, and nature of intervening terrain affect the technical microwave equipment requirements. The determination of antenna height and selection of antenna size, transmission line characteristics, transmitter power, and receiver sensitivity directly follow the objective for link reliability. In analog systems, the circuit loading, quality of equipment components and their installation, path design, and system length have a bearing on system noise performance (circuit quality), whereas, in digital systems, circuit quality is not greatly affected by loading or system length.

6.1.4.3 Equipment redundancy

To improve equipment availability, redundancy of critical components is employed. The redundancy is typically automatic, without the requirement for operator intervention. Redundancy is commonly referred to as ÒstandbyÓ operation. ÒStandbyÓ implies that the equipment items are fully redundant in the form of duplicate facilities that support functionality in spite of a failure in one of the items. ÒHot standbyÓ equipment items are powered continuously and may operate and function in parallel with, or independent of each other. For the latter scheme, when a primary failure occurs, the standby unit is switched on-line and the primary unit is switched off-line. Having both units powered-on decreases switchover time. ÒCold standbyÓ implies that the redundant components are powered only upon switchover. This method may be preferred when it is necessary to conserve site power (e.g., operation from solar energy). Examples of standby operation include transmitters, receivers, master oscillators/clocks, multiplexers, ampliÞers, and synchronization equipment.

6.1.4.4 Space diversity

SigniÞcant improvement in propagation reliability can be realized by using vertical space diversity of microwave antennas, especially for long paths. This is accomplished through the addition of a second antenna, which is typically installed below the primary antenna. For example, when operating at 6 GHz, diversity spacing is typically 9.14 m (30 ft). Separation may be more for lower frequency bands and less for higher frequencies, or, a speciÞc separation distance may be calculated to treat a particular path problem. For two- way communications, both ends of the path are treated. Most commonly, diversity is applied to receivers, although some schemes have been developed to independently switch transmitters to the diversity antenna.

6.1.4.5 Route diversity (ring or loop systems)

The microwave loop design discussed in 6.1.3 offers route diversity to improve propagation reliability and equipment availability. Route diversity can be quite effective in maintaining communications, owing to the fact that outages due to fading do not generally act simultaneously on multiple path segments. Virtual equip-

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ment redundancy is built into the diversity scheme without resorting to standby equipment components. For example, if a failure occurs to a Ònon-standbyÓ transmitter, receiver, or an antenna feeder system component in a loop network, the communications around the loop will switch directions and be maintained. Thus, route diversity loop operation may actually reduce system cost because redundant equipment can be minimized or eliminated from the system design.

6.1.4.6 Frequency diversity

Frequency diversity is another conÞguration that offers improved equipment and propagation reliability. In frequency diversity systems, dual transmitters and receivers are included in a common physical path. Each set of transmitters and receivers operates on a different radio frequency (RF). Since most signal fades are frequency selective, there will be minimal correlation of fades over the two communications channels and communications will be maintained with a high degree of reliability.

Frequency diversity schemes are spectrum inefÞcient and are not used to a great extent because they would obligate two frequency pairs or channels to carry identical information, and require a waiver from the FCC.

These systems are now rare. However, they may be encountered in military and international applications.

6.1.5 Network alarm, monitoring, and control

Network alarm, monitoring, and control are all deÞned by the user needs assessment. Central control requirements, level of monitor detail, and off-net accessibility are some of the considerations addressed in this subclause.

6.1.5.1 Central control

The central control point is the location where the primary alarm monitor is located. This location typically includes the master station of the alarm or monitor network. Statistical characteristics of the system (e.g., utilization and maintenance data) are available at this location, either in electronic form presented on a computer screen (CRT) or in printed hard copy form. This site usually includes the alarm master electronics, computer, monitor (display unit), keyboard, and printer.

Central control is a management position, best located at a central maintenance management site, that is responsible for the overall performance and control of the microwave communications system. Although this is a maintenance management tool, the primary qualiÞcations of the person responsible for this position should be technical or technical management. This is a critical position because the monitoring system is a sophisticated electrotechnology tool that is maintenance oriented.

Secondary master stations, or slave masters, should be employed for redundancy and/or monitoring and control functions during times when the central maintenance management site is not staffed. For a majority of microwave applications, knowledge of system faults is critical to continued system availability.

6.1.5.2 Detail level

The level of detail provided by the alarm system network is determined by the user needs assessment. The alarm system may be limited to worst-case indicators (e.g., no-transmit indications and open door alarms), or it can be a sophisticated microprocessor-driven alarm monitor and control system that allows the person responsible for the monitor position to change transmitters or receivers hundreds of miles away, or collect statistical data from any or all sites to determine failure trends. When integrated with control and preventive maintenance, the statistical data can provide the key to cost-effective minimum-failure-rate maintenance.

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6.1.5.3 Off-net access

Off-net access is determined by the user needs assessment. Off-net access is an alarm system design that allows access to the system status via a dial-in telephone interface with the primary system. This feature is important whenever public safety is a consideration or whenever the user needs determine that the microwave channel integrity is a critical factor. In addition, using a pager to alert someone in the event of a problem and having a dial-in system that allows this person to access the system, identify the problem, and possibly correct the condition, may result in cost savings in some systems by reducing shifts.

6.1.6 Permits

Sites are preselected based on their ability to communicate with adjacent sites. Once the initial site selection has been completed, site construction permits should be obtained or veriÞed to ensure that the sites selected are eligible for a construction permit. In the event that any one site cannot be permitted, alternate sites should be selected and veriÞed until all the sites chosen receive construction permits.

Because of the logistical problems associated with choosing alternate microwave sites, system planners should consider applying for a zoning waiver for a site if the process can be implemented in a timely and cost-effective manner.

In addition, FAA approval and FCC licensing should be accomplished or veriÞed early in the program. Any microwave communications system construction program hinges on the ability to obtain FAA approval, FCC licensing, and local construction permits for each site.

6.2 Channel requirements

Channel requirements are determined by the user needs assessment and affected by such factors as system conÞguration, number of site speciÞc I/O requirements, and the type of communications media requiring transport from one location to another.

6.2.1 Quality

System quality is determined by the user needs assessment and may be different for voice, data, and video applications. Analog channel loading, data rates, and path signal-to-noise ratios all affect channel quality in analog links. In digital links, due to digital modulation techniques, there are no effects associated with channel loading and channel data rates. In addition, due to forward error correction and error detection, digital links are mostly affected by low signal strength and signal-to-noise ratios near the receiversÕ thresholds.

6.2.2 Drops

Drops refer to the I/O circuits at each site. If a site requires one accessible voice line at that site, the microwave engineer includes the electronics to allow one microwave channel ÒdropÓ at that site.

The number of drops corresponds to the number of lines or circuits required by a site. Message (voice and data) circuit access in digital links is more complex than the direct-to-line analog link access at repeater sites.

6.2.3 Voice

Voice channels typically are the least demanding on a microwave system. There is usually a one-to-one correspondence between voice channels and microwave channels.

Voice channels are typically equivalent to telephone channels and may be either analog or digital.

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6.2.4 Data

Data lines are typically either voice frequency, modem type (analog, 300Ð3400 Hz), or direct digital facilities. Higher data rates can be accommodated by combining channels or by using higher (more complex) modulation schemes.

6.2.5 Video and teleconferencing

Video applications can be expected to consume the largest bandwidth or number of channels. Typically, channel requirements will vary from a one-to-one correspondence for low resolution applications to displac- ing 24 voice channels or more for one video channel.

Digital systems are better than analog systems at supporting compressed video and long-haul applications.

However, analog systems may be cost-effective for certain video applications.

6.3 Technical characteristics

Design of a microwave communications system evolves from the needs assessment and performance requirements. System technical speciÞcations or a list of technical characteristics are then established to identify the system requirements.

6.3.1 Analog

Currently, new analog microwave systems are typically 2 GHz links displaced by personal communications service (PCS) or relegated to low-capacity, low-cost applications. They represent mature technology, and industry offerings are diminishing in favor of digital alternatives.

As the capacity and/or size of analog networks increase, so does the concern over system performance. Con- sideration should be given to the noise degradation of voice, data, or video signals. Analog systems require signiÞcant attention to detail in their initial optimization and continued maintenance.

6.3.2 Digital

Digital microwave systems convert analog signals (voice) to digital information (0Õs and 1Õs). No conversion is required for digitized inputs.

Signal processing in the digitized environment is considerably more sophisticated than that used in analog systems. Digital microwave systems are easier to deploy and maintain, and are assuming a larger market share, which is likely to increase in the future.

6.3.3 Narrowband

Narrowband systems are applicable when the channel requirements are low. Narrowband systems are less costly than wideband systems and are FCC licensed on speciÞc channels designated for narrowband applications only.

Spread-spectrum radios are also applicable when the channel requirements are low. Typically capable of 24 to 48 voice channels, spread-spectrum radios provide an alternative to leased lines and 38 GHz microwave systems. Frequency coordination and FCC licensing are not required for spread-spectrum equipment certi- Þed under Part 15 of the FCC rules, thereby eliminating some of the time and cost associated with the construction of traditional microwave systems. However, users of spread-spectrum radios may be subjected to harmful interference received from other users, but may not cause harmful interference to users of other radio services.

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6.3.4 Wideband

Wideband systems are required when the number of channels deÞned in the user needs assessment exceeds a speciÞc number. These systems utilize speciÞc FCC designated wideband microwave channel allocations.

Wideband systems are more costly to construct and maintain than narrowband systems. However, wideband systems offer a lower cost per channel than narrowband systems, provided there is a need for the larger channel capacity.

Wideband applications typically include multiple video requirements, digital data requirements, and a large number of simultaneous voice channel requirements.

Long-term growth requirements should be considered when choosing a system. The selection of a wideband system is typical whenever the growth expectations indicate there will be a future need, especially in this era of Òinformation highwayÓ growth.

6.4 Microwave path requirements

Microwave path requirements are driven by the user needs assessment and include frequency selection, path proÞle calculations, reliability/probability calculations, and physical site surveys. Establishing reliable microwave paths is an iterative process that should start with an initial design and site selection, followed by site veriÞcation and any redesign if some sites prove to be unacceptable, followed by alternate site selection implemented as necessary.

6.4.1 Frequency band selection

Operating frequency selection is determined by channel requirements, geographic location/separation of sites, frequency availability, user eligibility, and climate/terrain characteristics.

6.4.2 Path proÞles

Microwave path proÞle calculations are site-to-site speciÞc and consider such factors as atmospheric conditions, foliage, frequency, path obstructions, and multi-path reßections. This is an analytical process that assists in the determination of path performance and integrity. Typically, the design engineer utilizes topo- graphical maps or high-resolution map databases, statistical information, equipment characteristics, etc., to establish microwave path performance.

6.4.3 Reliability calculations

Path reliability or outage probability calculations are based on the path proÞle calculations and the resulting signal strengths. The aggregate of the individual path calculations determines the total reliability of the system.

Reliability calculations consider temperature, humidity, and terrain characteristics for the area. The results are in the form of a percent or seconds of outage per year. Reliability is controlled by effective radiated power (ERP), path length, frequency band, antenna geometry, tower heights, and diversity arrangements, if used. Availability calculations consider the average rainfall in the area as well as equipment protection arrangements.

6.4.4 Physical path surveys

Physical path surveys are used to determine if the paper design is competent. Surveys should document the location of antenna towers, building structures, signiÞcant trees, and other landmarks or improvements asso-

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ciated with the microwave paths. The surveyor should provide all personnel, transportation, lodging, subsis- tence, surveying instruments, maps, etc., necessary to perform the work.

Survey activities should include the determination of the following:

Ñ Critical obstructions on-path and potential obstructions off-path;

Ñ VeriÞcation of terrain control points;

Ñ Reßection points, unblocked reßections, and bodies of water;

Ñ Expected tree growth along paths;

Ñ Site geographic coordinates;

Ñ Site elevations;

Ñ Recommended primary and diversity (if needed) antenna heights.

The results of the microwave path surveys should be presented in report form at the conclusion of the survey effort. The report should include the following documentation:

Ñ Data determined by the survey activities.

Ñ Antenna tower locations accurately depicted on 8.5 ´ 11 inch sections of USGS 1:24 000 topographic maps (or copies thereof). Proposed path azimuths should be depicted relative to True North.

Ñ ProÞle graphs for each path surveyed. Path proÞles are constructed using manually derived terrain data from USGS 1:24 000 topographic maps or by retrieving digitized terrain data. Terrain data is then updated by physical Þeld survey data. Path proÞles consider radio refractive index and depict critical obstructions, target height above obstructions, antenna centerlines, and line of sight.

Ñ Site plot plans depicting structures, landmarks, and improvements. Proposed path azimuths should be depicted relative to True North. The plot plans are not meant to serve as construction drawings, but should present the site features with reasonable accuracy.

Ñ Recommendations relative to the viability of the proposed microwave paths, reliability considerations, and/or alternate routings, and any suggestions that the surveyor deems appropriate to the project.

Coordination with the surveyor should commence in advance of the Þeld activities. Any questions or con- cerns Þeld personnel may have regarding the work to be performed should be directed to the project manager or technical professional, as appropriate.

6.5 FAA notiÞcation and approval

The FAA must be notiÞed of all construction that could be considered a hazard to aircraft navigation (FAA Form 7460). Radio or microwave towers greater than 60.96 m (200 ft) above ground level (AGL) will require FAA approval and must be marked and/or lighted in accordance with FAA rules. However, construction near airÞelds may require FAA approval and marking and/or lighting even when the maximum construction height will be well below 60.96 m (200 ft). It is therefore necessary to determine the need to Þle with the FAA for each site in the system. In addition, the FCC will require FAA approval for many tower sites based on FCC rules.

The procurement of large systems presents a logistical dilemma for the system planner and project manager.

FCC licensing usually requires FAA study approvals, and microwave communications sites should not be constructed if the site cannot be licensed. The time required to construct a large system is typically longer than the FCC license construction permit duration. If FCC licenses expire, a new FAA study must be requested and the entire site licensing process needs to be repeated from the beginning, usually causing a delay of at least 90 days. In addition, there is the possibility that, in certain areas where communications are heavily used, a site license may not be renewed because another applicant was able to obtain the frequency(s) during the time when the license had expired and was awaiting renewal.

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6.5.1 Location of airports

System design should include the location of each microwave tower. Each tower site must be acceptable to both the FAA and subsequently the FCC. Initial design should thus determine the best choice for each tower site and consider any airports or heliports located near these tower sites that may prevent construction. Pre- selection of sites can then be implemented by eliminating all sites that are obviously too close to airports and expected to be denied by the FAA. Submittals for FAA approval for selected sites will then have the best chance of a favorable determination from the FAA. However, before a complete system can be developed where all sites are approved by the FAA, several FAA application submittals may be required, followed by some denials, and then followed by reapplication for either modiÞcations to the same site or an application for a new site.

6.5.2 FAA designated approach and landing rules

Whenever a tower site is found to be located near an airÞeld, the FAA study is far more comprehensive than when the tower site is not located near an airÞeld. It should be expected that a more comprehensive study will require more time to complete than other site studies. The FAA applies special approach and landing rules for these studies and, typically, the expected disapproval rate and the time to secure a determination will increase. The FAA may also require a survey of the site to accurately identify the location for aeronauti- cal maps.

6.5.3 FAA application submittal and monitoring status

FAA applications should be monitored for both status and expiration. Although the FAA usually grants an extension for a properly submitted request, failure to extend can cause an application to expire. A new application must then be sent to the FAA if the site in question is still required.

6.6 FCC licensing requirements

Each microwave site is required to be licensed by the FCC. The licensing process includes pre-licensing activities (e.g., permitting, FAA studies, and frequency coordination). Recent changes to the FCC rules now permit operation of new or modiÞed point-to-point microwave station(s) prior to issuance of a license if the applicant is compliant with FCC Rules Part 101.

The procurement of large systems presents a logistical dilemma for the system planner and project manager.

FCC licensing usually requires FAA study approvals, and microwave communications sites should not be constructed if the site cannot be licensed. The time required to construct a large system is typically longer than the FCC license construction permit duration. If FCC licenses expire, a new FAA study must be requested and the entire site licensing process needs to be repeated from the beginning, usually causing a delay of at least 90 days. In addition, there is the possibility that, in certain areas where communications are heavily used, a site license may not be renewed because another applicant was able to obtain the frequency(s) during the time when the license had expired and was awaiting renewal.

6.6.1 Frequency coordination

Frequency coordination for microwave applications is a misnomer. The use of frequency coordination is loosely applied to microwave applications because the frequency engineering analysis required by the FCC for microwave applications is similar to the frequency coordination required for other frequency bands. The required frequency engineering analysis is typically performed by private engineering Þrms that specialize in microwave application assistance and are generally considered to be microwave frequency coordinators.

Frequency coordination is a required precursor by the FCC before a microwave application will be considered for FCC authorization. The purpose of frequency coordination is to ensure that the frequency selected for each microwave site will not cause harmful interference to other licensees in the microwave band.

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6.6.1.1 Interference analysis

The frequency coordinator provides a frequency coordination statement that the prospective FCC microwave licensee is required to submit with the FCC license application. One element of this coordination statement is an interference analysis statement consisting of a list of licensees considered in the interference analysis.

Interference analyses should consider intra-system interference as well as interference caused to, or received from other geographically adjacent microwave systems. Many microwave frequency bands also require the coordinator to coordinate with existing licensees in the proximity of the microwave path prior to any license application to the FCC.

6.6.1.2 Fees

All applicants can expect to pay a fee for frequency coordination. Licensing fees may be required for certain FCC services. Fees should be determined during the planning stage of a project. The cost may be substantial.

6.6.1.3 Frequency coordination submittals

When submitting a request for frequency coordination to an FCC approved frequency coordinator, the applicant should include the following information:

a) Applicant information (e.g., name, address, etc.);

b) Equipment technical information (e.g., make, model numbers, and performance speciÞcations, including but not limited to antennas, transmission lines, and microwave radios);

c) Spectrum information (e.g., band preference, and emission designators);

d) Site information, (e.g., antenna height, latitude, longitude, and ground elevation).

6.6.1.4 System description

The system description should include both a written and a graphical presentation of the complete system, including site information such as latitude, longitude, and antenna orientation.

6.6.2 FCC licensing

FCC licensing must precede activation of any microwave transmitter. To secure an FCC microwave license, an applicant must submit an application to the FCC for each site license, accompanied by a frequency coordination report and, if applicable, an FAA determination. Certain applicants are exempt from license fees;

however, it is recommended that applicants verify fees and exemptions before applying as the fee rules can change at any time.

6.6.2.1 System description

A formal system description should be prepared and accompany the FCC license application. This description should be graphic and present detailed system information.

6.6.2.2 Coordination information attachment

The coordination information attachment is a required attachment to the FCC license application. This attachment is provided by the frequency coordinator and includes the following:

a) A statement of prior coordination (where applicable);

b) A supplemental statement showing other users identiÞed and considered by the coordinator;

c) The technical information required on the FCC application (Technical Information Section, currently Section 3 on FCC Form 402).

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6.6.2.3 FCC license application preparation

The FCC application for station authorization should be prepared accurately. If there is any doubt about the applicationÕs completion, or if the applicant is not familiar with the process, the applicant should contract the work to a qualiÞed communications consultant or professional service specializing in microwave license preparation.

6.7 Facility requirements

Facility requirements are a major planning consideration and cost determining factor. Facilities will vary considerably from project to project and region to region. A checklist (punch list) should be developed during the initial planning stages to ensure that all planned requirements are met. Many of these requirements can be large cost items (e.g., equipment shelter, antenna structure, and public utility access). Environmental siting constraints (e.g., contaminated soil, wetland requirements, endangered species protection, etc.) are also important and should be considered during the site selection process.

6.7.1 Site geotechnical analysis

Typically, a site geotechnical analysis is required to provide ground material characteristics for each site.

Soil borings are obtained to provide design data for the tower, foundation, and ground system engineering.

6.7.1.1 Soil boring

Soil borings provide the tower designer with the information needed to design the tower foundations. There- fore, soil borings should precede design and can considerably affect the cost of the foundations.

6.7.1.2 Electrical resistivity

Ground resistivity characteristics can be determined from the soil boring samples and help pre-determine certain grounding system design requirements (e.g., ground-system surface area). In addition, electrical resistivity (megger tests) measurements can be used to more accurately describe near-surface conditions when appropriate.

6.7.1.3 Corrosion

Ground corrosion characteristics are determined from the soil boring samples and help predetermine certain grounding system design requirements such as the materials used for grounding and bonding and foundation design. National standards (e.g., ANSI/EIA/TIA 222-E-1991)⁸ speciÞcally address considerations for cathodic protection as opposed to cathodic disintegration.

6.7.2 Communications tower requirements

Communication tower requirements should include, but not be limited to height, wind loading, location, and type or style.

6.7.2.1 Solid versus hollow member design

Towers are available in either solid leg construction (angular or tubular) or hollow member construction (typically tubular). The advantages of hollow tubular towers are cost and weight. The advantage of solid leg construction is that there can be no hidden corrosion. In addition, solid tubular designs exhibit lower wind

8Information on references can be found in Clause 2.

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loading characteristics, while ßat angular tower members exhibit lower voltages and lower radiation during a lightning attachment.

6.7.2.2 Guyed versus self-supporting

There are two basic tower designsÑguyed towers and self-supporting towers. The guyed tower requires external support from the guy wires. The self-supporting tower is a free-standing design that requires no external support.

Typically, the guyed tower is used when either low cost or very tall heights are a design requirement. Self- supporting towers are used when there is limited site space or when high wind loading and low heights are speciÞed.

6.7.2.3 Wind loading

Tower wind loading is a major design consideration affected by site speciÞc requirements (e.g., antenna surface area, radial ice potential, and building codes). Wind loading is an extremely important design consideration, having considerable cost impact, and should be determined for both the short-term and long-term needs of the applicant. Basic wind load requirements are established in ANSI/EIA/TIA 222-E-1991 and ASCE 7-95. However, local building codes may have more stringent design requirements.

6.7.2.4 Ice loading

Ice loading affects the total wind loading and initial design considerations of any tower that may experience icing. This consideration is important to towers constructed in ice-prone areas, but can usually be ignored in tropical and subtropical regions.

6.7.2.5 Antenna loading

Antenna loading affects the total wind loading and initial design considerations of any tower. Antenna loading is a function of surface area and can usually be found in the antenna manufacturerÕs speciÞcations. Also, ice loading should be considered in addition to the manufacturerÕs wind loading speciÞcations for ice-prone areas.

Antenna stability requirements (usually microwave antennas) may place severe twist and sway requirements on the tower design, which can have a signiÞcant impact on tower cost.

6.7.2.6 Tower lighting

Tower lighting is often a requirement. Unless a local law or ordinance requires obstruction lighting, obstruction lighting should be provided only if the FAA requires it. Lighting can be either in the form of incandescent beacons or in the form of medium- to high-intensity strobe lights.

6.7.2.6.1 FAA requirements

The FAA will prescribe lighting requirements in response to the application submitted to the FAA for a spe- ciÞc tower site. The FAA will speciÞcally deÞne, if required, the type of tower lights required. It is normal for the FAA to specify incandescent beacon lighting; however, the FAA will usually approve the use of strobe lighting if requested in writing by the applicant.

6.7.2.6.2 Red lighting

Red lights traditionally utilize a red-lens-covered incandescent bulb(s) that is either continuous or pulsed (ßashed) at regular intervals. The continuous red light is called an obstruction light. The ßashing red light is

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called a beacon. Typically, as a towerÕs height increases, FAA rules will require both obstruction lights and beacons at speciÞed height intervals to assist pilots in determining approximate tower height in low-light conditions. The beacon system is very popular and, until the advent of the strobe light, was the only FAA approved system in use. Manufacturers now offer an equivalent red strobe for beacon applications.

6.7.2.6.3 Strobe lighting

Strobe lights typically have a longer bulb life than incandescent lights and therefore tend to require less maintenance. Strobe lighting utilizes a highly visible light that is ßashed (strobed) at regular intervals. The system converts the utility power to a very high voltage, which is then applied to the strobe light. FAA rules delineate the location and number of strobe lights required on each tower. Installation of strobe systems must be FAA approved.

The interests of nearby building occupants, especially for high-rise buildings, should be considered when using strobe lights. These lighting systems can sometimes be a source of irritation to such residents, and thus initiate a requirement for an environmental assessment per FCC Rule, Part 1, Paragraph 1.1307(8).

6.7.2.6.4 Dual-lighting systems

Dual-lighting systems usually consist of strobe lights in the daytime and incandescent red beacons or red strobes at night. This system has become popular because the initial cost of tower painting, and the associated maintenance and repainting, can be eliminated. In addition, many experts feel that dual-lighting systems provide an aesthetically more pleasing tower by eliminating the need for painting, and by avoiding the use of white strobe lights at night. Although the initial cost of strobe lighting hardware is usually greater than incandescent beacons, there is a long-term beneÞt from lower recurring costs associated with energy con- sumption and maintenance. To determine the most cost-effective choice, the engineer should consider location, tower height, and operation/maintenance costs.

6.7.2.7 Obstruction painting

Tower obstruction painting is required by the FAA, along with tower lights, when a tower is deemed a spe- ciÞc hazard to aircraft navigation. Obstruction marking is very consistent and uses only two colorsÑinterna- tional orange and white. Each marked tower is required to have one international orange stripe at the top of the tower and one international orange stripe at the bottom of the tower. The remainder of the stripes alternate between white and international orange. The total number of stripes normally equals seven, except when towers are very tall. Tower obstruction marking paint is a special paint having a unique FAA speciÞca- tion that should be addressed in any bid or RFP. Obstruction painting may not be required if strobe lighting is used. Tower paint quality must be maintained to FAA and FCC standards; therefore, the tower requires repainting throughout its life.

6.7.3 Communications shelter requirements

Microwave towers normally are constructed at locations strategic to the needs of the microwave path. Equip- ment housing considerations tend to be a secondary priority. Therefore, it is only a coincidence when a microwave tower is located close enough to an existing building that has enough space and utility services to adequately accommodate the microwave and ancillary equipment.

6.7.3.1 Size

Equipment shelters are commonly included with the construction of microwave towers. Each tower site should be considered unique, and each shelter should provide both adequate internal vertical clearance and ßoor space for the initial equipment design, as well as additional space for expected growth for the life of the system (10Ð30 years).

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The construction materials of the equipment shelter should be adequate to last the life of the system. Also, special construction speciÞcations for shelters planned for remote areas, or in areas of high risk may have additional design speciÞcations (e.g., bullet-resistant construction and special security fencing). Shelters that must be ßown into a mountaintop site should also include extraordinary structural strength. Other requirements for site-speciÞc needs can only be deÞned on a site-by-site basis. It should be noted that shelter design also affects shelter foundation design, which in turn affects cost.

6.7.3.3 Wind loading

SpeciÞcations for building wind loading may also be an issue, especially in some areas where building codes specify wind loading. Building wind loading speciÞcations should be based on the same wind loading requirements used for the microwave tower (typically ANSI/EIA/TIA 222-E-1991 or ASCE 7-95).

6.7.3.4 Permitting

In some locations, the local jurisdiction may also require a special building permit, even when the equipment building is prefabricated and meets a state standard. Each site-speciÞc case can be a unique permitting task.

Therefore, each should be researched during the design stage to avoid delays and additional costs that would occur in the event that a site permit was disapproved after plans were Þnalized, or a construction contract was signed that stipulated an unacceptable site.

6.7.3.5 Grounding

Each building should include speciÞcations for grounding, bonding, and lightning protection. Each site should have a minimum amount of grounding and, where there is a high incidence of thunderstorms and especially lightning occurrences, the minimum should be increased, as required, to provide adequate protection. Building grounding and bonding along with lightning protection should be considered mandatory requirements of any microwave site installation.

6.7.3.6 Insulation

Building insulation should be considered in accordance with each site location and the operating temperature speciÞcations of the equipment housed in the building. Typically, both heating and air conditioning is included in each building. Building insulation usually reduces the recurring energy cost associated with maintaining a constant building temperature and, therefore, should be part of a system planning cost analysis.

6.7.3.7 Heating, ventilation, and air conditioning

System design should include the heating, ventilation, and air-conditioning (HVAC) requirements for each site building. Heat generated by the enclosed equipment should be offset by building air-conditioning. In cold climates, ambient low temperatures in winter tend to cool the internal building temperature below acceptable levels. Building heating should increase internal temperatures to at least the minimum design- speciÞed level.

6.7.3.8 Fire suppression systems

Fire suppression systems can provide a considerable cost savings in the event of a Þre at an unmanned site, as well as provide a safer environment at a manned site. In addition, potential insurance savings should also be considered against the cost of the Þre suppression system.

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Some prefabricated buildings either include Þre suppression systems, or offer these systems as options to the purchaser.

6.7.4 Power and emergency power requirements

Many sites and applications either will require special power service requirements due to their remote locations, or will require emergency power sources to ensure that there is no loss of sensitive services.

In the event that a site requires emergency power (e.g., batteries and/or motor-driven generator), additional issues such as, but not limited to, auto-transfer switching, location of devices, fuel storage, and EPA regula- tions should also be addressed.

6.7.4.1 Main power source

The most common site power source is supplied by the local public service utility company. However, some remote sites are designed to utilize power from generators or solar-powered/battery systems.

6.7.4.2 Emergency generator requirements

Emergency generator design requirements should include existing equipment power needs, future growth equipment power needs, and HVAC power requirements. In addition, a power margin of safety should be added to the generator size to accommodate the air-conditioning start-up current. Uninterruptible power system (UPS) units require special generator sizing, and their use should be considered during the system design phase. Emergency power can also be provided by portable or mobile generators that can be transported from site to site on an as-needed basis. This strategy may signiÞcantly reduce initial emergency power equipment procurement costs, but could fail to provide an adequate number of emergency generator systems in the event of multiple site outages (e.g., wide area blackout or storm damage).

6.7.4.3 Fuel requirements

Power generators can be fueled by gasoline, diesel, liqueÞed petroleum (LP) gas, or natural gas. Fuel requirements for the emergency generator should be decided upon during the design phase to ensure that all costs and site-speciÞc needs are considered.

6.7.4.4 Battery requirements

If batteries are selected as the emergency power source, adequate battery power (ampere hours) and charging capacity should be speciÞed in the design phase.

6.7.4.5 Outage limitations

Often a combination of batteries and a power generator are used as the best compromise between continuous power (battery) and long-term backup power (generator).

Fuel capacity and battery capacity determine the length of time the power can be maintained to support system operation. Outage limitation is a design factor and is reßected in fuel or battery capacity speciÞcations.

6.7.5 Surge and lightning protection

The need for surge and lightning (transient) protection is directly related to the location of the microwave site and the electronic technology utilized at that site. Lightning protection engineering is a specialized Þeld, and the selection of a qualiÞed engineer cannot be ignored. Protection design is dependent on the thunder- storm days and lightning events at each site, and the type of electronic technology needing protection. As technology tends to low-voltage signal levels, transient protection should increase. In all cases, initial instal-

IEEE Guide for Microwave Communications System Development: Design, Procurement, Construction, Maintenance, and Operation

IEEE Guide for Microwave Communications System Development: Design,

Procurement, Construction, Maintenance, and Operation

Introduction

Contents

IEEE Guide for Microwave Communications System Development: Design,

Procurement, Construction, Maintenance, and Operation

1. Overview

2. References

3. Acronyms

4. Professional assistance requirements

5. Assignment of responsibility

6. Design requirements