电信专业英英词典F-2_电脑电信

　focal length - distance from the exact center of the dish to the center of the feed.

　focal point - the physical point in space toward which the satellite reflector dish directs the received signal so it can be processed.

　format - this is (1) the general makeup and organization of a file, or (2) the arrangement of bits of characters within a group.

　forum - this is a section of a website or online service, wherein you can communicate with other forum members about a common subject.

　forward - this is the act of redirecting a particular email, an entire email address, or a telephone number.

　forward error correction (fec) - the purpose of this element is to add unique codes to the digital signal at the output source so problems can be detected at the signal receiver.

　freeware - this is software that is free to use and distribute. some freeware, though, requires that you don't make any changes or alterations to the code.

　frequency - the number of times that a wave or wave-like process goes through its complete cycle per second of time. frequency is measured in hertz (hz), which is one cycle per second.

　frequency band - this is a particular band of frequencies in the electromagnetic spectrum, expressed in hertz, in which satellite signals are transmitted.

　frequency coordination - a process that is implemented to attenuate frequency interference between different satellite networks.

　frequency division multiplexing - this is an older method of dividing the bandwidth available for transmission into distinct narrow bands for individual transmission channels.

　frequency modulation (fm) - the signal carries the desired information by varying the frequency of the carrier wave.

　frequency shift keying (fsk) - this is another modulation technique (see frequency modulation) used to transmit data. it shifts the frequency above and below the carrier frequency (representing 1 and 0, respectively).

　frequency spectrum - this is a range of frequencies (and is similar to bandwidth).

　fsk - see frequency shift keying.

　full duplex - this is the same as duplex and is simultaneous transmission of data in two opposite directions.