Hennessey RS622: FM broadcasting
FM broadcasting is a VHF broadcasting technology, pioneered by Edwin Howard Armstrong, which uses frequency modulation (FM) to provide high-fidelity sound over broadcast radio. The term "FM band" describes the frequency band in a given country which is dedicated to FM broadcasting. This term is slightly misleading, since it equates a modulation method with a range of frequencies.
Market concentration
World War I brought home to nations the strategic importance of long-distance radio; in addition to its military uses in keeping contact with its fleets and overseas forces, a country that didn't have radio could be isolated by an enemy cutting its submarine telegraph cables. In the US, before the war, the radio industry was fragmented by patent monopolies held by competing giant firms, so the best long-range radio technology was owned by two European firms: the British Marconi Co. and the German Telefunken. At its entry into the war in 1917, the US government temporarily took control of the entire US radio industry for the war effort, including the transatlantic wireless stations of these foreign firms. After the war, due to fear of foreign ownership of the US radio industry, there was an abortive effort to create a federal radio monopoly.Hennessey Audio
Hennessey RS622 for sale: Stereo separation
In order to preserve stereo separation and signal-to-noise parameters, it is normal practice to apply pre-emphasis to the left and right channels before encoding, and to apply de-emphasis at the receiver after decoding.
Stereo FM signals are more susceptible to noise and multipath distortion than are mono FM signals.
In addition, for a given RF level at the receiver, the signal-to-noise ratio for the stereo signal will be worse than for the mono receiver. For this reason many stereo FM receivers include a stereo/mono switch to allow listening in mono when reception conditions are less than ideal, and most car radios are arranged to reduce the separation as the signal-to-noise ratio worsens, eventually going to mono while still indicating a stereo signal is being received.
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Microbroadcasting
Low-power transmitters such as those mentioned above are also sometimes used for neighborhood or campus radio stations, though campus radio stations are often run over carrier current. This is generally considered a form of microbroadcasting. As a general rule, enforcement towards low-power FM stations is stricter than AM stations due to issues such as the capture effect, and as a result, FM microbroadcasters generally do not reach as far as their AM competitors. Hennessey IV
Hennessey HD1102:Digital services
Digital services are now also available. A 57 kHz subcarrier (phase locked to the third harmonic of the stereo pilot tone) is used to carry a low-bandwidth digital Radio Data System signal, providing extra features such as Alternative Frequency (AF) and Network (NN). This narrowband signal runs at only 1187.5 bits per second, thus is only suitable for text. A few proprietary systems are used for private communications. A variant of RDS is the North American RBDS or "smart radio" system. In Germany the analog ARI system was used prior to RDS for broadcasting traffic announcements to motorists (without disturbing other listeners). Plans to use ARI for other European countries led to the development of RDS as a more powerful system. RDS is designed to be capable of being used alongside ARI despite using identical subcarrier frequencies.
