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Morse code is called the original digital mode. Radio telegraphy, designed for machine-to-machine communication is the direct on / off keying of a continuous wave carrier by Morse code symbols, often called amplitude-shift keying or ASK, may be considered to be an amplitude modulated mode of communications, and is rightfully considered the first digital data mode.
With communication satellites used for long-distance communication links, current troposcatter systems are employed over shorter distances than previous systems, use smaller antennas and amplifiers, and have much higher bandwidth capabilities. Typical distances are between 50 and 250 kilometres (31 and 155 mi), though greater distances can be ...
Ground wave is important for radio signals below 30 MHz, but is generally insignificant at higher frequencies where line-of-sight propagation dominates. AM and longwave broadcasting, navigation systems such as LORAN, low-frequency time signals, non-directional beacons, and short-range HF communications all make use of
Broadcasting uses the tropical broadcast bands between 2.3–5.06 MHz, and the international broadcast bands between 3.9 and 6.2 MHz. Military NVIS communications mostly take place on 2–4 MHz at night, and 5–7 MHz during daylight. Optimum NVIS frequencies tend to be higher towards the tropics and lower towards the arctic regions.
ATV includes the study of building of such transmitters and receivers, and the study of radio propagation of signals travelling between transmitting and receiving stations. [3] ATV is an extension of amateur radio. It is also called HAM TV or fast-scan TV (FSTV), as opposed to slow-scan television (SSTV).
The coaxial collinear (COCO) antenna uses transposed coaxial sections to produce in-phase half-wavelength radiators. [5] A Franklin array uses short U-shaped half-wavelength sections whose radiation cancels in the far-field to bring each half-wavelength dipole section into equal phase. Another type is the omnidirectional microstrip antenna (OMA ...
The use of "ham" meaning "amateurish or unskilled" survives today sparsely in other disciplines (e.g. "ham actor"). The amateur radio community subsequently began to reclaim the word as a label of pride, [15] and by the mid-20th century it had lost its pejorative meaning. Although not an acronym or initialism, it is often written as "HAM" in ...
Note that different countries have different rules; for example, in the United States, the two-meter band is 144–148 MHz, while in the United Kingdom (and most of Europe) it is 144–146 MHz. Repeater frequency sets are known as "repeater pairs", and in the ham radio community most follow ad hoc standards for the difference between the two ...