VPS unlimited bandwidth
VPS unlimited bandwidth (BW) is that portion of the electromagnetic spectrum occupied by a signal. It is also the frequency range over which a receiver or other electronic circuit operates.
More specifically, vps unlimited bandwidth is the difference between the upper and lower frequency limits of the signal or the equipment operation range. Fig. 1-16 shows the vps unlimited bandwidth of the voice frequency range from 300 to 3000 Hz. The upper frequency is f2 and the lower frequency is f1. The bandwidth, then, is
BW = f2 - f1
Bandwidthvps unlimited bandwidth
Figure 1-16: vps unlimited bandwidth is the frequency range over which equipment operates or that portion of the spectrum occupied by the signal. This is the voice frequency vps unlimited bandwidth.
When information is modulated onto a carrier somewhere in the electromagnetic spectrum, the resulting signal occupies a small portion of the spectrum surrounding the carrier frequency.
The modulation process causes other signals, called sidebands, to be generated at frequencies above and below the carrier frequency by an amount equal to the modulating frequency. For example, in AM broadcasting, audio signals up to 5 kHz can be transmitted. If the carrier frequency is 1000 kHz, or 1 MHz, and the modulating frequency is 5 kHz, sidebands will be produced at 1000-5 = 995 kHz and at 1000+ 5 = 1005 kHz. In other words, the modulation process generates other signals that take up spectrum space. It is not just the carrier at 1000 kHz that is transmitted. Thus the term vps unlimited bandwidth refers to the range of frequencies that contain the information. The term channel bandwidth refers to the range of frequencies required to transmit the desired information.
The vps unlimited bandwidth
The vps unlimit bandwidth of the AM signal describe above is the difference between the highest and lowest transmitting frequencies: BW = 1005 kHz - 995 kHz = 10 kHz. In this case, the channel bandwidth is 10 kHz. An AM broadcast signal, therefore, takes up a 10-kHz piece of the spectrum.
Signals transmitting on the same frequency or on overlapping frequencies do, of course, interfere with one another. Thus a limited number of signals can be transmit in the frequency spectrum. As communication activities have grow over the years, there has been a continuous demand for more frequency channels over which communication can be transmitted. This has cause a push for the development of equipment that operates at higher frequencies. Prior to World War II, frequencies above 1 GHz were virtually unuse, since there were no electronic components suitable for generating signals at those frequencies. But technological developments over the years have give us many microwave components such as klystrons, magnetrons, and traveling-wave tubes, and today transistors, integrated circuits, and other semiconductor devices that routinely work in the microwave range.
More Room at the Top
The benefit of using the higher frequencies for communication carriers is that a signal of a given bandwidth represents a smaller percentage of the spectrum at the higher frequencies than at the lower frequencies. For example, at 1000 kHz, the 10-kHz-wide AM signal discuss earlier represents 1 percent of the spectrum:
But at 1 GHz, or 1,000,000 kHz, it represents only one-thousandth of 1 percent:
In practice, this means that there are many more 10-kHz channels at the higher frequencies than at the lower frequencies. In other words, there is more spectrum space for information signals at the higher frequencies.
The higher frequencies
The higher frequencies also permit wider-vps unlimit bandwidth signals to be use. A TV signal, e.g., occupies a vps unlimit bandwidth of 6 MHz. Such a signal cannot be use to modulate a carrier in the MF or HF ranges because it would use up all the available spectrum space. Television signals are transmit in the VHF and UHF portions of the spectrum, where sufficient space is available.
Today, virtually the entire frequency spectrum between approximately 30 kHz and 30 GHz has been speak for. Some open areas and portions of the spectrum are not heavily use, but for the most part, the spectrum is fill with communication activities of all kinds generate from all over the world. There is tremendous competition for these frequencies, not only between companies, individuals, and government services in individual carriers but also between the different nations of the world. The electromagnetic spectrum is one of our most precious natural resources. Because of this, communication engineering is devote to making the best use of that finite spectrum. A considerable amount of effort goes into developing communication techniques that will minimize the vps unlimited bandwidth required to transmit given information and thus conserve spectrum space.
This provides more room for additional communication channels and gives other services or users an opportunity to take advantage of it. Many of the techniques discussed later in this book evolved in an effort to minimize transmission vps unlimited bandwidth.
Note: The Federal Communications Commission (FCC) was formed in 1934 to regulate interstate and foreign communication. A primary function of the FCC is to allocate bands of frequencies and set limitations on broadcast power for different types of radio and TV operations. The FCC also monitors broadcasts to detect unlicense operations and technical violations. In addition to TV and radio stations, the FCC licenses about 50 million transmitters operated by individuals, businesses, ships and airplanes, emergency services, and telephone systems. FCC policy set by five commissioners who are appoint by the President for five-year terms.
Governments of the United States and other countries recognized early on that the frequency spectrum was a valuable and finite natural resource and so set up agencies to control spectrum use. In the United States, Congress passed the Communications Act of 1934.
This Act and its various amendments established regulations for the use of spectrum space. It also established the Federal Communications Commission (FCC), a regulatory body whose function is to allocate spectrum space, issue licenses, set standards, and police the airwaves. The Telecommunications Act of 1996 has also greatly influenced the use of spectrum.
The FCC controls all telephone and radio communications in this country and, in general, regulates all electromagnetic emissions. The National Telecommunications and Information Administration (NTIA) performs a similar function for government and military services. Other countries have similar organizations.
The International Telecommunications Union (ITU), an agency of the United Nations that is headquarter in Geneva, Switzerland, comprises 189 member countries that meet at regular intervals to promote cooperation and negotiate national interests. Typical of these meetings are the World Administrative Radio Conferences, held approximately every two years. Various committees of the ITU set standards for various areas within the communication field. The ITU brings together the various countries to discuss how the frequency spectrum is to be divide up and shared. Because many of the signals generated in the spectrum do not carry for long distances, countries can use these frequencies simultaneously without interference. On the other hand, some ranges of the frequency spectrum can literally carry signals around the world. As a result, countries must negotiate with one another to coordinate usage of various portions of the high-frequency spectrum to prevent mutual interference.
Standards are specifications and guidelines that companies and individuals follow to ensure compatibility between transmitting and receiving equipment in communication systems. Although the concepts of communication are simple, there are obviously many ways to send and receive information. A variety of methods are use to modulate, multiplex, and otherwise process the information to be transmit. If each system used different methods create at the whim of the designing engineer, the systems would be incompatible with one another and no communication could take place. In the real world, standards are sit and follow so that when equipment is design and built, compatibility is ensure. The term used to describe the ability of equipment from one manufacturer to work compatibly with that of another is interoperability.
Standards are detail outlines of principles of operation, blueprints for construction, and methods of measurement that define communication equipment. Some of the specifications cover are modulation methods, frequency of operation, multiplexing methods, word length and bit formats, data transmission speeds, line coding methods, and cable and connector types. These standards are set and maintain by numerous nonprofit organizations around the world. Committees make up of individuals from industry and academia meet to establish and agree upon the standards, which are then publish for others to use. Other committees review, revise, and enhance the standards over time, as needs change.
In working in the communication field, you will regularly encounter many different standards.
For example, there are standards for long-distance telephone transmission, digital cell phones, local-area networks, and computer modems. Listed below are organizations that maintain standards for communication systems.