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Appendix: More on Why Community Stations Must Stay on FM As stated in the main body of the NCRF submission document, the NCRF strongly opposes the proposal to move South African community radios from FM to AM/MW frequencies. Moving community stations away from their existing FM frequencies to AM/MW frequencies would very seriously undermine stations’ operations and sustainability The general technical arguments for why FM, and not AM/MW, is the appropriate medium for South African community radio broadcasters, have been made in Section 1 of the main body of the NCRF submission document. This appendix goes into more depth on those technical arguments. FM and AM/MW - Introduction Radio waves are broadcast in a number of bands which each contain a range of frequencies and have different ways of travelling from point to point through the Earth's atmosphere. FM and AM/MW broadcast frequencies operate in different ways and have very different characteristics The difference is in how the carrier wave is modulated, or altered. With AM/MW radio, the amplitude, or overall strength, of the signal is varied to incorporate the sound information. With FM, the frequency (the number of times each second that the current changes direction) of the carrier signal is varied. The different characteristics of AM/MW and FM broadcasting influence the appropriate use of the two different types of frequencies. One important characteristic of the frequencies is related to the reaction to the ionosphere. AM/MW and FM frequencies have different ionospheric refraction. AM/MW waves refract off the ionosphere, meaning that they stay within the Earth’s atmosphere. FM waves on the other hand, go through the ionosphere, and disappear into space. Appendix – More on Why Community Stations Must Stay on FM 1 Comparison between the main FM and AM/MW Characteristics: Susceptibility to slight changes in amplitude Dynamic range, frequency response Stereo capability Broadcast range Increased night-time ionospheric refraction Transmitter power, cost FM With an FM broadcast, slight changes in amplitude don't matter, because the audio signal is conveyed through changes in frequency; the FM receiver just ignores changes in amplitude. The result: no static at all. FM radio, which came into being in the 1930's, uses a different approach than AM. Its virtually immune to any type of external interference, it has a greater dynamic range, and it can handle sounds of higher and lower frequencies. AM/MW With an AM/MW broadcast, changes in amplitude result in static. FM broadcasting is a low-power, low cost technology.This is because FM waves can AM/MW is a higher-power, higher-cost technology. This is because Conclusion Audio quality is far higher with an FM broadcast than with AM/MW. A lower quality sound would be highly destructive to community stations. FM’s better dynamic range and frequency response makes it much better than AM/MW for broadcasting music, which has much greater frequency ranging than the human voice. Music sounds much better on FM radio. FM provides high audio quality suitable for both voice and music (community radios are typically licensed to carry 60% talk and 40% music). Stereo Non-stereo FM allows for a stereo signal, which is also essential to quality music broadcasting. All music recorded in the last 40 years is intended to be played in stereo. FM waves pass through AM/MW waves refract AM/MW is good for long-range the ionosphere. They are off the ionosphere, broadcasting, rather than generally line-of sight. bending around the short-range. FM is ideal for Earth. short-range, small-footprint broadcasting. South African community radios generally operate in small footprints, making FM the more appropriate broadcast system. FM is not noticeably Because of increased Dealing with night-time affected by the night-time ionospheric ionospheric refraction adds ionospheric refraction, refraction, at sunset it is complexity and costs to AM/MW and thus is not noticeably often necessary for transmission, and if the refraction affected by the rise in AM/MW radio stations is not properly dealt with, the such refraction in the to reduce power and signal is jeopardised. Community evenings. directionalise their stations will be much better able signal in order to avoid to achieve transmission skills interference with other sustainability, and financial radio broadcast signals sustainability, using FM (which is not affected by night-time ionospheric refraction) AM limits the loud-to-soft range of sounds that can be reproduced (called “dynamic range”) and the high-to-low sound frequency range (called “frequency response”) Appendix – More on Why Community Stations Must Stay on FM South African community radio stations that do their own FM signal transmission are able to do so with low-cost, low-power 2 travel far even when transmitted by a low-power transmitter. Set-up costs The main costs of setting up an FM transmission system are the transmitter, the mast, and simple cabling and grounding. AM/MW waves need much more power than FM waves to reach their destination. AM/MW transmitters are high-power, and much more expensive than the FM transmitters needed to cover the same broadcast footprint. transmitters – often 250-watt transmitters. Others pay a monthly fee to Sentech to send out their FM signals. Setting up an AM/MW transmission system not only requires a much more expensive transmitter, but also a series of connected masts, large land space, and expensive cabling and grounding systems. Setting-up a full AM/MW transmission system would be prohibitively expensive for a community-owned radio. Community stations would not be able to raise the money necessary to own their own high-power AM/MW transmitters. If they paid Sentech to send out their AM/MW signals, the Sentech monthly fees would be unsustainably high. One of the goals of the South African community radio movement is for all stations to own their own transmission systems, in order to safeguard their independence. Pushing community radio stations onto AM/MW frequencies would seriously undermine this goal. Technical Explanation A Step Back The reason FM outperforms AM/MW in audio quality is that AM is amplitude-modulated, making it unable to send a clear stereo signal. FM does not have this problem, because it modulates the carrier frequency. As a result, you get more information, i.e. full frequency range, frequency response, and a stereo signal. The spectrum of the audible frequencies (20-20KHZ) with FM is covered (depending on limiting and clipping etc.) at around 2000-16000 Hertz, whereas AM is limited in the spectrum, with the high and low frequencies getting "cut off". Typically, you have around 6-8 times more effective bandwidth in FM transmission than in AM/MW transmission. (Note: AM means “Amplitude Modulation” a modulation technique; MW means “Medium Wave,” which is the band/frequency on which AM is carried. For the purposes of this submission, we mostly refer to them together, as “AM/MW.” FM means “Frequency Modulation,” carried on what are known as FM frequencies.) In the mid 1930s, Inventor Edwin Armstrong saw that several problems existed with AM frequency broadcasting: static interference from household appliances and lighting limited audio quality (frequency response and dynamic range) night-time interference between many stations (co-channel interference), because of ionospheric refraction, especially in rural areas. So he invented FM. . Appendix – More on Why Community Stations Must Stay on FM 3