Can you add one? Add another edition? Copy and paste this code into your Wikipedia page. Need help? Electronic communication systems Roy Blake. Donate this book to the Internet Archive library.
If you own this book, you can mail it to our address below. Not in Library. Want to Read. Check nearby libraries Library. Share this book Facebook. Last edited by ImportBot. January 15, History. An edition of Electronic communication systems Written in English — pages. Subjects Telecommunication. Libraries near you: WorldCat. Electronic communication systems First published in Subjects Telecommunication. Table of Contents Introduction to communications systems Radio-frequency circuits Amplitude modulation Angle modulation Transmitters Receivers Digital communication The telephone system Data transmission Local-area networks Wide-area networks and the Internet Digital modulation and modems Multiplexing and multiple-access techniques Transmission lines Radio-wave propagation Antennas Microwave devices Terrestrial microwave communication systems Television Satellite communication Cellular radio Personal communication systems Paging and wireless data networking Fiber optics Fiber optic systems.
Edition Notes Includes index. Commercial radio broadcasting in both the United States and Canada began in Early radio transmitters were too cumbersome to be installed in vehicles. The first such system to be considered practical was installed in Detroit in Two-way police radio, with the equipment occupying most of the car trunk, began in the mids. Ampli- tude modulation AM was used until the late s, when frequency modu- lation FM began to displace it.
World War II provided a major incentive for the development of mobile and portable radio systems, including two-way systems known as walkie- talkies that could be carried in the field and might be considered the dis- tant ancestors of todays cell phones. FM proved its advantages over AM in the war. PostwarExpansion Soon after the end of World War II, two systems were developed that pres- aged modern wireless communication. This was an expensive service with limited capacity, but it did allow true mo- bile telephone service.
This system is still in use in some remote areas, where, for instance, it allows access to the PSTN from summer cottages. Initially it used frequencies near MHz, but in that respect it was ahead of its time, since equipment for the UHF range was prohibitively expensive. Frequencies in the MHz band were allocated in , and CB radio immediately became very popular. The service was short- range, had no connection to the PSTN, and offered users no privacy, but it was and still is cheap and easy to set up.
The popularity of CB radio has de- clined in recent years but it is still useful in applications where its short range and lack of connectivity to the rest of the world are not disadvantages. For example, it serves very well to disseminate information about traffic problems on the highway. Meanwhile another rather humble-appearing appliance has become ubiquitous: the cordless phone. Usually intended for very short-range com- munication within a dwelling and its grounds, the system certainly lacks range and drama, but it does have connectivity with the PSTN.
Most cordless phones use analog FM in the and MHz bands, but some of the latest models are digital and operate at either MHz or 2. Cordless phones are cheap and simple to use, but their range is limited and, except for the digital models, they offer little privacy. Pagers were introduced in The first models merely signaled the user to find a telephone and call a prearranged number. More recent models can deliver an alphanumeric message and even carry a reply.
Though rela- tively limited in function, pagers remain very popular due to their low cost and small size. Cellular systems are quite differ- ent from previous radiotelephone services such as IMTS in that, instead of using a single powerful transmitter located on a tall tower for wide coverage, the power of each transmitter is deliberately kept relatively small so that the coverage area, called a cell, will also be small. Many small cells are used so that frequencies can be reused at short distances.
Of course, a portable or mobile telephone may move from one cell to another cell during the course of a conversation. In fact, this handoff may occur several times during a conversation. Practical cellular systems had to await the development of computers fast enough and cheap enough to keep track of all this activity. Theoretically at least, the number of users in a cellular system can be in- creased indefinitely, simply by making the cells smaller.
The first cellular systems used analog FM transmission, but digital mod- ulation schemes, which provide greater privacy and can use bandwidth more efficiently, are used in all the new systems. These personal communi- cation systems PCS usually operate in a higher frequency range about 1.
Current cellular systems are optimized for voice but can also transmit data. In the near future, high-speed data transmission using PCS is expected to become a reality. At this point, however, the past merges into the future, and well resume the discussion later in this book. Since radio can- not be used directly with low frequencies such as those in a human voice, it is necessary to superimpose the information content onto a higher fre- quency carrier signal at the transmitter, using a process called modulation.
The inverse process, demodulation, is performed at the receiver in order to re- cover the original information. The information signal is also sometimes called the intelligence, the modulating signal, or the baseband signal.
An ideal communication sys- tem would reproduce the information signal exactly at the receiver, except for the inevitable time delay as it travels between transmitter and receiver, and except, possibly, for a change in amplitude.
Any other changes consti- tute distortion. Any real system will have some distortion, of course: part of the design process is to decide how much distortion, and of what types, is acceptable. Simplexand Duplex Communication. Electronic Communications Networks.
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