Volume_5_-_RF_Transmission_and_Antenna_Systems_Standards.doc

Volume 5 – RF Cables Antennas Coax and Isolation Standards USDA Forest Service

Chief Information Office

Radio System Technical Standards

Volume 5

RF Cables Antennas Coax and Isolation Standards

Prepared for USDA Forest Service

FINAL Version 2.0.3 14 December 2007

Prepared by:

Radio Modernization Program Team

DOCUMENT HISTORY

RELEASE

LABEL

Brad Mitchell, Team Lead

Debra Marohn, Tech Writer Dave Johnson

Don J Schnee

Duane Kierstead Gary B Paustian Jim Byrd

Kary Mavencamp

Mark Hooper

Tommie J. Cluff

REviewers

TABLE OF CONTENTS

11.0 Introduction

11.1 Industry Standards

22.0 Radio Frequency Transmission and Antenna System Guidelines

32.1 Standardization and Installation Quality

32.1.1 Connectors

42.1.2 Cable

52.1.3 Cable Preparation and Connector Installation

62.1.4 Cable Installation

72.1.5 Transmission Line Grounding

72.1.6 Duplexers

72.2 Antenna Selection

82.2.1 Standard Antenna

82.2.2 Non-Standard Antenna

82.3 Antenna Mounting

93.0 Minimizing Transmission System Degradation and Environmental Influence

Section 1

1.0 Introduction

Volume 5 provides uniform direction for service area technicians and radio system installation teams and establishes technical standards for RF Cables Antennas Coax and Isolation. The implementation of these standards will result in high-level performance of radio systems across the Forest Service.

This volume provides minimal standards for coaxial cable and antenna systems for Forest Service radio communications equipment and applies to all new Forest Service radio system installations. Existing radio systems that do not meet the standards established in this volume will be identified and brought into compliance in conjunction with normal site maintenance, project work, or during normal lifecycle replacement. If the standards cannot be met, adequate technical documentation to support this conclusion will be maintained in the site files within the service area.

The implementation of these modernization standards will result in more reliable radio systems across the Forest Service, providing more consistent radio communications, and increasing personnel safety by providing highly reliable, high-quality radio communications.

1.1 Industry Standards

General guidelines from industry standards as well as existing Forest Service standards have been selected for use in this document.

1. The Forest Service will use the Motorola R56 Standards and Guidelines for Communications Sites, where applicable to the Forest Service and when practical to do so. Not every item from the R56 manual applies to Forest Service needs. The R56 standards were derived from specifications written by standards organizations including the National Fire Protection Association (NFPA), Underwriters Laboratories (UL), and the Occupational Safety and Health Administration (OSHA), and are commonly accepted as industry standards for telecommunications facilities.

2. In addition to the Motorola R56 standards, Forest Service guidelines were derived from National Electrical Code (NFPA 70) and Standard for the Installation of Lightning Protection Systems (NFPA 780). It is recommended that all personnel responsible for the installation, testing and maintenance of Forest Service RF transmission and antenna systems reference the Motorola R56, NFPA 70, and NFPA 780 standards for more detail on the subjects contained in this document.

section 2

2.0 Radio Frequency Transmission and Antenna System Guidelines

This section contains general guidelines and requirements for Forest Service communications site antenna and RF transmission systems.

The operational goal of the Forest Service is to install high quality RF transmission systems. When such systems are used, RF power loss is inevitable. The goal is to design and install antenna systems so that minimal loss of power occurs between the output of the radio and input of the antenna. This is referred to as “loss in the power budget.” Even though power loss can be compensated for by using a higher gain antenna, there is often a trade-off with narrower vertical and horizontal beam width with higher gain antennas, which can actually reduce radio coverage in the desired areas. With this in mind, a certain amount of loss is sometimes unavoidable, and the acceptable limit for loss in all newly designed RF transmission systems will be less than 6db.

Sites with a single repeater should use a duplexer and single antenna. Sites with multiple repeaters may use a Tx/Rx combiner, or Tx Combiner/Rx multicoupler in lieu of using duplexers. Sites that have multiple transmitters will also utilize a dual-stage isolator, followed by a harmonic filter on the repeater transmitter.

Base stations will use a single antenna and operate in simplex mode using a TR Relay (even though they may have separate transmit and receive frequencies). In radios where this functionality is not built into the radio, an antenna relay will be used to connect to a single antenna. Dual-stage isolators will be installed on base stations, followed by a harmonic filter when there are multiple transmitters at a site or when there are any other interference issues that warrant their use. Additional filtering may be required on the receiver if interference or desensitization is problematic. Figure 2-1 shows a typical repeater site RF transmission and antenna system.

Figure 2-1 TYPICAL REPEATER SITE RF TRANSMISSION AND ANTENNA SYSTEM

2.1 Standardization and Installation Quality

Equipment will be installed per manufacturer’s recommendations and will adhere to the guidelines detailed below. At sites with User Group standards, the requirements of the User Group and the Forest Service will be fulfilled.

2.1.1 Connectors

2.1.1.1 Connector weather-proofing

All outdoor connectors shall be weatherproofed using materials rated for outdoor use in one of the following four methods:

1. Heat-shrink tubing manufactured with sealing compound in the heat-shrink.

2. Sealed completely with pliable sealant compound (e.g., Butyl Mastic), then wrapped with electrical tape.

3. Stretch sealing tape (e.g., Hercu-Stretch, which has a neoprene jacket combined with an inner butyl mastic layer).

4. Cold-shrink tubing used in combination with butyl mastic sealant.

2.1.1.2

Connector selection The N-type connector is the standard connector that shall be used for all transmission lines at base stations and repeater sites. All equipment should be procured with N-type connectors to avoid the need to use between-series adapters; the proper gender of connectors will be used on cables to avoid the need for gender-changing adapters. Every connection induces some loss and these measures will minimize power loss.

Neither between-series nor gender-changing adapters will be used in a system transmission line. Crimp or compression type connectors may be used with either solder or non-solder (captivated) center pins. It is critical that the connector used must be specifically designed to match the cable used, and the connectors must be properly installed according to manufacturer’s instructions using the proper tools (i.e., proper crimpers and proper prep tools). Crimp connectors are as mechanically sound as any other mechanically secured connectors if the proper crimp and preparation tools are used, and likewise either type can be improperly installed as easily as the other. The major manufacturers of the connectors used predominately by the Forest Service have verified that there is no difference in performance between connectors that use solder center pins versus those that use non-solder, captivated type pins.

2.1.2 Cable

The specifications for cables outlined in this volume provide guidance for towers up to a height of 400 feet. In all cases, foam-filled, solid core (i.e., conductor) cable shall be used. At a minimum, cable will have the following characteristics:

· No greater than 1 db of loss per 100 feet at 150 MHz

· 50 Ohm Impedance

· UV resistant polyethylene jacket

· 100 percent shield coverage providing at least 90 db shielding efficiency

2.1.2.1 VHF Cable Runs

The following specifications shall be used for VHF cable runs. Although the ratings listed are for 150 MHz, the figures for cable run length are calculated for the Forest Service's highest operational VHF frequencies. Using cables that meet these loss specifications will ensure the maximum line loss in cable is 3db or less on cable runs at our highest VHF operating frequencies. Larger cable sizes may be used if the system loss budget requires it.

2.1.2.2 UHF Cable Runs

The following specifications shall be used for UHF cable runs. Although the ratings listed are for 450 MHz, the figures for cable run length are calculated for the Forest Service's highest operational UHF frequencies. Using cables that meet these loss specifications will ensure the maximum line loss in cable is 3db or less on cable runs at our highest UHF operating frequencies. Larger cable sizes may be used if the system loss budget requires it.

Note: Cable runs over 360 feet will require additional engineering.

2.1.3 Cable Preparation and Connector Installation

All Service Area technicians will maintain a serviceable set of coax tools for the connectors and cable they use. This tool set shall contain, at a minimum, the following:

1. Crimpers and die designed specifically for the crimp connector being used

2. Proper cable cutter pliers

3. Proper cable prep tools to prepare cables for connector installation

4. Mid-span strip tools for grounding kits

2.1.4 Cable Installation Requirements

The following are recommended general requirements for cable installation:

1. Cables will be secured to tower and ice bridges at a maximum distance of every 3 feet. Cables will be secured with mechanical clamps designed for the type of cable being used, which physically attach to the tower structure and secure the cable via mechanical means.

2. Tie wraps will not be used to secure cables outdoors.

3. Cables will not be installed in a manner that would impede climbing or safety devices, and will not be attached to ladders, pegs, or any other safety devices.

4. Cables spanning more than 3 feet from the antenna tower to the building entry panel will be protected/supported by an ice bridge.

5. Cables will be installed with a drip loop falling at least 8 inches below the building entry port at the point where the cable transitions from the vertical to horizontal. Where possible, entry into the building entry port, or boot, will be at an upward angle from the drip loop. When forming drip loops, care should be taken to ensure minimum bend radius for the cable being used is observed. An example of a drip loop is illustrated in Motorola R56 Standard, Section 4.9.

6. All RF cables will be labeled within 6 inches of each end, or as close as possible if obstructions prevent labeling within 6 inches. Cables will be marked cables with colored electrical tape at the top (antenna) end, middle of tower, and cable entry point to provide for easy identification.

7. Cable used for RF jumpers within the facility will be minimum 3/8 inch foam core coax, with a maximum loss of 1.5db/100 feet. Jumpers will be made with the proper gender of N-connector to avoid the requirement for gender-changing adapters. Smaller, high-quality jumper cables provided by manufacturers as component inter-connect cables may be used.

8. Cables will be run up the inside of the tower in a manner that will not impede the climbing path.

9. Cables will be secured inside the facility at least every 2 feet. Cable racks/ladders will be installed between the equipment racks and cable entry point where practical. Cables will be routed to minimize intrusion of working space around the equipment racks, while keeping cable jumper length to a minimum.

10. Grounded cable entry panels will be installed for cable entry into buildings. If facility construction prevents this, at a minimum cable will be routed from the outside to the inside of the facility through a conduit. If the conduit method of entry is used, the conduit will be sealed around the cable on the inside and outside of the facility.

11. Antennas mounted for non-backbone subscriber type radios, such as desktop base stations that have antennas mounted on the buildings, poles, or other non-standard mounting methods will satisfy all the grounding and cable support requirements outlined above using the appropriate hardware for the situation.

2.1.5 Transmission Line Grounding

Transmission line will be grounded per R56 Standards. At a minimum, the cable shall be grounded at the top of the cable run near the antenna, and at the bottom of the tower using grounding kits manufactured for the cable being used. Ground kits shall be installed at equal distance between the top and bottom so that there will be a maximum of 75 feet between ground kits. An additional grounding kit shall be installed and grounded at the facility external ground bus unless the bulkhead panel provides for direct grounding of the cable. Properly grounded lightning arrestors with N-Type connectors shall be installed on all cable runs inside the building at the building entry point for the cables. Refer to Grounding and Lightning Protection Guidelines for USDA Forest Service Communications Shelters for further details on grounding of transmission line and all other radio equipment.

2.1.6 Duplexers

All repeaters will use a duplexer and operate with one antenna, or may use a Tx/Rx combiner or Tx combiner/Rx multicoupler operating on multiple antennas when repeaters are co-located. At sites with numerous radio transmitters, dual-stage isolators will be installed on the transmitters. Duplexers and combiners used will be mounted in equipment racks, unless prohibited by facility size. In such cases, the equipment will be securely mounted to some supportive structure off the floor of the shelter. Mounting to external walls of the shelter will be used only as a last resort if there are no other options. This will minimize transfer of outdoor temperature changes to the duplexers through the walls. Duplexers and combiners used shall have the following characteristics, as a minimum:

· Mountable in a 19 inch rack

· Minimum of 70db isolation between transmit and receive

· Maximum insertion loss of 2db

· Maximum VSWR 1.5:1

· All connectors will be N-Type

2.2 Antenna Selection

Antenna selection can be a complicated subject with many factors coming into effect. At a minimum, the site location in relationship to the desired coverage area and the primary use for the site need to be considered. Antennas should be selected during the site design phase of the radio replacement and review cycle.

2.2.1 Standard Antenna

The standard antenna type to be used shall be a vertically polarized, unity or low (i.e., less than 3dBi) gain antenna. As a minimum, the standard antenna shall have a vertical beam width of at least 70 degrees and omni-directional radiation pattern. These antennas are normally lightweight, easy to mount, provide low load and wind resistance on the towers, and are sturdy and economical.

2.2.2 Non-Standard Antenna

All antennas other than those described above will be considered non-standard. Non-standard antennas may be used, but their use will be limited to situations in which their use is clearly warranted and documented. Some antenna types in this category that may be used are open bay dipoles, high gain dipoles, or Yagi antennas. When these types of non-standard antennas are used, technicians will document the technical information that led to the determination for the need to use that particular antenna. This not only ensures that antenna selection is based on a thorough analysis, but also serves to document site-specific selection criteria that will enable future technicians to understand the logic of why a particular antenna is required at each site.

2.3 Antenna Mounting

Antennas will be mounted using appropriate mounting standoffs and hardware designed for the type of tower and antenna being mounted. Antennas shall be mounted so that antenna elements are at least 18 inches from the tower structure.

Section 3

3.0 Minimizing Transmission System Degradation and Environmental Influence

A properly designed communications site uses preventive measures to minimize and eliminate interference at locations in which radio signals can mix and create intermodulation or broadband problems. In many cases, physical installation practices can lead to system degradation and increase the vulnerability and effects of these signals on a system. Although not all of these measures are directly related to the RF transmission system, they present physical conditions that can lead to degraded performance of the system if not kept in check. The following preventive measures will be followed to help minimize radio interference:

· All materials used at a radio site must be free of rust.

· Braided wire will not be used because it can corrode and provide a source for intermodulation.

· Metal-to-metal connections must be rigid.

· Any loose metal should be removed from the site.

· All metal fencing must be grounded (IAW R56, 6.4.2). Vinyl clad fencing is recommended.

· Connections of dissimilar metals should be avoided. If such a connection is necessary, the connection will be thermal bonded.

· Metal or plastic cable ties will not be used on any tower. This also includes “hose clamps.” Exception: “Hose clamp” type clamps are acceptable for mounting cable standoff brackets as prescribed by the manufacturer, or for connecting cable ground kit leads as outlined in R56, Figure 6-30.

· Plastic cable ties used internal to the building are acceptable; metal cable ties are not.

· All old, abandoned, or out of service coaxial cable (i.e., feedline) will be removed from the site, with the exception of cable that will be used as inactive spare/emergency use cable.

· All inactive spare or dedicated cable will be terminated and weatherproofed at both ends. All cables will be inspected annually for physical condition and acceptable performance, and must be secured properly.

Original Requirements Sign-Off Sheet

I have read the above document and will abide by its terms and conditions and pledge my full commitment and support for the project.

ISO Communications Line of Service Manager: /S/Michael Field 18 May 2007

(Mike Field) Date

IRM Radio Program Architect: /S/ Larry D. Wade_____________May 21, 2007

(Larry Wade) Date

UNCLASSIFIED

Vol 5 Page 5-2 Release 2.0.1 CIO Radio System Technical Standards 8 November 2007

UNCLASSIFIED

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