Wednesday, March 9, 2011
【 Weak current College 】 electromagnetic spectrum (a) 】
Keywords: electromagnetic wave spectrum
Time: location: user: label type: operating frequency: standard: implementation of the company: solution providers: hardware providers:
【 Summary 】 electromagnetic spectrum (1)
Different bands of the electromagnetic wave propagation modes and features vary, their purpose is different. In the radio frequency allocation is important to note that interference problems. Because of the electromagnetic wave is characterized in accordance with their band, in addition to the spread of any law to constrain it. Therefore, if two radio stations with the same frequency (F) or extremely similar frequency and works in the same area (S), same time period (T), it will cause interference. Because modern radio frequency available range is limited and cannot be freely without order, and you want to carefully plan. So many people in foreign countries, the spectrum as the nature of a resource, make use of the frequency spectrum. A, spectrum utilization
The so-called spectrum utilization has two aspects. Namely: (1) the allocation of the frequency spectrum. Upcoming frequency depending on the business to be assigned, in order to avoid confusion in the use of frequencies; (2) spectrum savings.
From spectrum utilization point of view, since the total spectrum range is limited, each of the radio frequency spectrum shall endeavour to reduce, in order to accommodate more radio and reduce interference. This requires to compress each radio bandwidth, decrease the interval between the channel and reduce spurious emission.
Because of electromagnetic wave propagation in the world, so you will need to have an international agreement to address. Cannot be separately identified in a particular country. Therefore, to have a dedicated international meeting to discuss these and make recommendations or requirements. At the same time, due to the continuous development of science, the Division is continuously changing. Historically,on spectrum allocation of Conference have repeatedly, such as: 1906 1912, Berlin, London, Washington, 1927, 1932, Madrid, Cairo, 1938, 1947, Atlantic City and 1959 Geneva Conference.
Figure 1 ITU World frequency division
Figure 1 1959 Geneva meeting of the world is divided into three frequency partition map. 1 area for Europe and Africa; 2 areas for North and South America; 3 area to Asia and Australia.
ITU headquarters in Geneva, Switzerland on its Internet website at: http://www.itu.int. 2. frequency distribution of international institutions
Now for frequency assignment work by the world Organization of the International Telecommunication Union (ITU). It has: the international radio Consultative Committee (CCIR), to research-related technical issues and make recommendations; international frequency register (IFRB), responsible for the international use of the frequency of the registration management.
Consider the frequency of distribution and use is mainly based on the following points: (1) each band propagation characteristics of electromagnetic waves. (2) the characteristics of a variety of business and common requirements. Other conditions but also the history, technology development, and so on. Third, the radio business types
Following on the use of radio frequencies for business to do simple description:
(1) fixed communications business: fixed-point to communicate business.
(2) air fixed-point communications business: Air's secure flight have need of targeted traffic.
(3) broadcast service: includes sound radio and television broadcasting. Electro-voice broadcasting frequency bandwidth of 10 kHz, TV frequency bandwidth of 8 MHz (some countries for 6 MHz).
(4) mobile communications business: the mobile radio (on-board, ship-borne, airborne, etc) and land-based radio or mobile radio communication between the radio.
(5) aeronautical mobile communications business: air stations with aircraft radio communications, or communications between the aircraft.
(6) the maritime mobile communications business: in the shore-ship, or between the radio communications between ships.
(7) land-based mobile communications business: in the land mobile and base stations, or between a land mobile radiocommunication between.
(8) radio navigation business: radio navigation (including maritime and air navigation), direction, and other services. It requires a steady and uninterrupted work, and don't allow the blind spot (quiet zone).
(9) radio positioning business: generally refers to radar.
(10) space communications business: at the ground stations and space (satellite or space) or between the communication between the space station.
(11) radio astronomy business: is for radio astronomy with a business. Radio astronomy mainly observe stellar radiation of electromagnetic waves by, for example, the observation of single atoms of hydrogen of radiation (1420.405MHz) and so on.
(12) weather service: weather for radio communications, such as advertised meteorological reports, etc.
(13) the amateur radio service: abroad, there are amateur radio radio communication or research. These international is recognized, and specify the appropriate frequency.
(14) standard frequency business: send highly accurate for science and technology used standard frequency.
(15) timing signal business: the height of the advertised accurate signal timing.
(16), branch, medical frequency: in industry, science or medical often need to use high frequency current. Because their power is often very large, in order to prevent interference to communications, now also set aside certain frequency to use.
The above paragraph (11), (12), (14), (15) business is recognized should not be interfered with. Therefore, assigned to the business use of the frequency, other business should not be used, or only without disturbing conditions before use.
Radio frequency is usuallyAccording to the frequency level (i.e. the length of the wavelength) to divide the band. Band of standard does not fully consolidated, there are several slightly different partition method. Band Division usually as shown in table 1.
In addition, in the microwave band is also popular with an approach based on wavelength division band method, as shown in table 2. This Division was based on a military radar operating frequency (wavelength) confidentiality requirements, they only addressed a radar frequency bands of the work, not specifically its specific frequency. Subsequently the microwave components working frequency range and this Division has some form of hooks. Table 3 gives the microwave band new old name cross reference table. The primary information source for references:
 jianglin. Summary of radio wave propagation and spectrum utilization. Beijing: defense industry press, 1974
 Liu Yang Wang Yu-Min. automatic train identification system principles and applications-Beijing: China railway Publishing House, 2003