The Communications Handbook / Edition 2 available in Hardcover
- ISBN-10:
- 0849309670
- ISBN-13:
- 9780849309670
- Pub. Date:
- 04/29/2002
- Publisher:
- Taylor & Francis
- ISBN-10:
- 0849309670
- ISBN-13:
- 9780849309670
- Pub. Date:
- 04/29/2002
- Publisher:
- Taylor & Francis
Hardcover
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Overview
From fundamental theory to state-of-the-art applications, The Communications Handbook covers more areas of specialty with greater depth that any other handbook available.
- Telephony
- Communication networks
- Optical communications
- Satellite communications
- Wireless communications
- Source compression
- Data recording
Expertly written, skillfully presented, and masterfully compiled, The Communications Handbook provides a perfect balance of essential information, background material, technical details, and international telecommunications standards. Whether you design, implement, buy, or sell communications systems, components, or services, you'll find this to be the one resource you can turn to for fast, reliable, answers.
Product Details
| ISBN-13: | 9780849309670 |
|---|---|
| Publisher: | Taylor & Francis |
| Publication date: | 04/29/2002 |
| Series: | Electrical Engineering Handbook Series |
| Edition description: | REV |
| Pages: | 1616 |
| Product dimensions: | 7.00(w) x 10.00(h) x (d) |
About the Author
Read an Excerpt
68: The Earth Station
Power DistributionReliability of the power system is another major concern for the Earth station. Depending on the application, different levels of primary and backup power systems may be required. To increase reliability, some Earth stations use two different sources of commercial power from the utility company that are fed from different grids. The electrical service entrance must be properly sized by calculating the load for all anticipated equipment. The calculated load should include ancillary systems such as antenna deicing and heating, ventilation, and air-conditioning (HVAC) systems. The electric service entrance should also be equipped with surge protectors to help guard against equipment damage from lightning strikes. The Earth station equipment building or shelter should be designed so that sufficient room is provided for the power distribution equipment required. It is sometimes helpful to provide separate distribution for critical and noncritical loads. When backup systems are used there are sometimes capacity limitations that require noncritical systems to remain off-line during power outages.
One or more outboard engine generators (Fig. 68.5) may be used to supply primary or standby power. If a generator is planned, the required capacity should be calculated by determining the initial total site load and the potential for growth. The maximum rate of fuel consumption per hour can then be calculated and a fuel storage tank can be sized accordingly. Consideration must be given to the placement of a fuel tank so that it remains accessible at all times for refueling. Local ordinances may stipulate whether the tank can be above orbelow ground and they will also dictate if special spill containment basins will be required. Newly installed underground tanks will require automatic leak detection systems and double-walled piping to comply with recent federal Environmental Protection Agency (EPA) rulings. As part of a standby generator system, an electrical or mechanical transfer switch will need to be installed. The transfer switch will sense a failure of the incoming utility power feed and automatically place the generator on-line. Because of the initial current demand placed on a generator at the moment of transfer, time-delay relays can be installed to stagger the start-up time of high-current devices such as air-conditioner compressors. This arrangement can help keep the line frequency stable especially on generators that use a mechanical governor system. Electrical governors tend to provide better line regulation under varying loads.
Earth stations which utilize electric heaters on the antennas for deicing may wish to include an option for using either the commercial AC power or the standby generator to supply power. Using the generator for powering deicing systems is a good way to exercise the unit under an actual load condition.
It is a good idea to include remote alarms on the generator to monitor critical parameters such as oil pressure, water temperature, and fuel level. Most generators have built-in alarms that will initiate a shutdown if a dangerous situation occurs. However, few generators have factory installed pre alarms to alert the user to a potential shutdown condition. It is also a good idea to have the generator vendor install pre alarms so that the Earth station operator can take corrective action be taken before a shutdown occurs.
Critical Earth station components can be powered from an uninterruptable power system (UPS). An UPS system will keep electrical service from being interrupted while backup generators come on-line during a power failure. As with a standby generator, the UPS system should have the capacity to accommodate all of the existing and anticipated site load. It may not be practical or economically feasible to run the entire Earth station from UPS power. In this case, the electrical distribution should be planned to route the UPS system to critical loads only.
Satellite transmission equipment is often designed with redundant power supplies. The UPS system can be used as one source of power to feed the equipment, and the utility power can be used as the other source. This will prevent an interruption to transmission if one power source fails.
An important part of any installation will be the grounding system. Grounding must conform to the National Electrical Code. A poor ground system becomes a safety hazard for personnel working at the site and also increases the risk of damage from a lightning strike. All antenna systems should be grounded and if a tower is used for microwave interconnection, it should also be grounded. Equipment racks in the Earth station shelter or building should be tied into the same ground system as all of the outdoor equipment.
68.5 Batteries h In some applications storage batteries are used to power equipment in the event of commercial AC failure. Storage batteries will also be part of an UPS system. Batteries must be properly housed and maintained to ensure safe, reliable operation. Instructions provided by the battery manufacturer " should always be followed regarding the storage, installation, and maintenance of batteries.
The temperature of the batteries will affect their ability to deliver power under load and can also limit their overall life expectancy. In general, the batteries should be located in an area that will be kept ; between 72° and 78°E Earth station design should include a separate room for batteries to provide,: a proper environment and safe operation. Local ordinances will address any special requirements for battery room designs such as spill containment or explosion-proof fixtures. Entrance to battery. rooms should be restricted to maintenance personnel only and no one should be permitted to enter y the room without proper safety clothing and eye protection. Special safety equipment including eye wash stations and clean-up equipment should be located in every battery room.
68.6 Antenna Foundation Requirements
The antenna manufacturer will provide specific information regarding the foundation requirement for each particular model. Because of the complexity of foundation design, it is recommended that a professional engineer be consulted. The information provided by the antenna manufacturer include wind loading data and anchor bolt patterns. These should be provided to the foundation engineer before the design process begins.
For antennas requiring a reinforced concrete foundation or "pad," the engineer must take several items into consideration. Soil bearing capacity should be measured from samples obtained at the site. Once an excavation is made, additional samples may be taken from the base to determine if any special soil reinforcement is required prior to the construction of the foundation. The engineer will specify the minimum strength that the concrete must achieve after curing. This will be based on the analysis of wind load requirements and the soil condition. The design of the pad should also specify any steel reinforcements required.
The installation contractor should be familiar with local zoning and building ordinances and obtain all of the necessary permits before work begins. The contractor should also be provided with a survey of the site to ensure proper placement of the foundation. It is essential that the foundation is orientated correctly so that the desired portion of the satellite arc can be reached. Placement of each antenna foundation should be carefully planned so that any future antenna installations will not have a portion of their desired arc coverage obstructed by existing antenna installations.
As construction progresses, the foundation will be framed (Fig. 68.6) and a template can be laid out for the setting of anchor bolts before the concrete is poured. Most antenna manufacturers will provide a template to speed the layout of the anchor bolts. Test cylinders should be taken by the contractor while the concrete is being poured. These cylinders are normally tested by an independent laboratory after the concrete is cured to determine the strength it has achieved. The concrete strength needs to meet or exceed the figure specified by the design engineer before the antenna can be erected.
Site Heating, Ventilation, and Air-Conditioning
Adequate heating and cooling must be provided at the Earth station site to prevent equipment failures from occurring. In a small Earth station shelter, redundant window style air conditioners may be sufficient for cooling. If heating is required, a small wall-mounted electric furnace will usually work well...
Table of Contents
Basic Principles. Telephony. Networks. Optical. Satellite. Wireless. Source Compression. Data Recording. Index.What People are Saying About This
"The Communications Handbook is an extensive, scholarly, professional level resource to the practical applications of electrical engineering technology for telephones, communication networks, data recording, source compression, and much more. The Communications Handbook is strongly recommended as being an utterly exhaustive reference resource which is packed from cover to cover with extensive in-depth science and technical applications."
—Michael's Bookshelf
"An extensive revision of the first edition reflects many significant developments that have taken place in communications and electrical engineering over six years. . . Like its original release, this edition boasts an international list of contributors from industry and academic research centers. . . Serving as a dictionary, encyclopedia and reference work containing many bibliographic references, this volume stands out as a major tool because it can accompany textbooks and other resources or easily stand on its own as an authoritative work. . . This title should be available in at least one format in all academic libraries and large public libraries."
—Julie Gelfand, University of California Irvine Science Library