Montage Acoustics BT4480: Microbroadcasting

Montage Acoustics Speakers: Modulation
Frequency modulation is a form of modulation which conveys information over a carrier wave by varying its frequency (contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant). In analog applications, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. This form of modulation is commonly used in the FM broadcast band.

Shortcomings of AM broadcasting
AM radio was often noisy. There was no protection from static created by lightning, electrical equipment, and other sources of signal pollution. Especially at night, conflict between nearby and distant stations using a single frequency was common, and required many smaller stations to operate at much reduced power after sundown. Finally, the 10 kilohertz minimum separation between stations in the United States limited fidelity to sounds much lower than the upper limit of human hearing, and the advent of high-fidelity recording equipment created a demand for high-fidelity radio.

As a result of these shortcomings, especially the noise issue, RCA in 1934 hired Edwin Howard Armstrong to test his FM broadcasting system, which started to be deployed in the 1940s, but because of a channel allocation change in 1946 would not achieve dominance over AM until the end of the 1970s.Montage Acoustics reviews

Montage Acoustics BT4480: 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.

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Medium-wave frequency
Medium-wave (medium frequency, MF) and short-wave (high frequency, HF) radio signals act differently during daytime and nighttime. During the day, MF signals travel by groundwave, diffracting around the curve of the earth over a distance up to a few hundred kilometers from the signal transmitter. However, after sunset, changes in the ionosphere cause MF signals to travel by skywave, enabling radio stations to be heard much farther from their point of origin than is normal during the day. This phenomenon can be easily observed by scanning the medium wave radio dial at night. As a result, many broadcast stations are required as a condition of license to reduce their broadcasting power significantly (or use directional antennas) after sunset, or even to suspend broadcasting entirely during nighttime hours. Such stations are commonly referred to as daytimers. In Australia medium wave stations are not required to reduce their power at night and consequently stations such as the 50,000-watt 3LO can be heard in some parts of New Zealand at night. Montage Acoustics

Montage Acoustics Speakers: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.