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en:selectivity [2018/10/29 19:42] (aktuell)
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 +===== Selectivity =====
 +The capability of a receiver to separate one signal from another on an adjacent frequency channel is referred to as selectivity.
 +In the technical documentation,​ the selectivity is often referred to as bandwidth; the frequency difference which will cause asignal on an adjacent channel a signal level drop of -6 dB, partly also -60 dB is states. A lower value for the - 6 dB 8and the - 60 db) will stand for a more narrow bandwidth filter.
 +In the shortwave range, the radio stations appear relatively close to each other with a channel spacing of 5 kHz. A station a channel only 5 kHz away from the operation frequency can severely affect the signal, causing an unpleasant whistling tone in this example with a pitch of 5 kHz. On medium waves, this phenomenon with a channel spacing of 9 kHz (international) resp. 10 kHz (in the US) is less pronounced, on FM with a channel spacing of 50/100 kHz, adjacent channel interference is only a problem with very weak signals in the vicinity of a "​boomong strong signal"​.
 +It is important to choose the optimum bandwidth for reception: For AM reception of broadcasting stations, IF filters with a width of 4 - 6 kHz perform well, for SSB reception 1.8 - 3 kHz, for CW reception are very narrow filters of 250 - 500 Hz used.
 +Coil filters can be produced cheaply, but they perform well only on low intermediate frequencies,​ higher quality filters which are also inexpensive to manufacture are ceramic filters. The narrow and steep flank quartz filters become more expensive and the best results are achieved in short-wave receivers with mechanical filters.
 +In some receivers, a continuously variable bandwidth (BWC) has been realized; with the modern DSP technology (digital signal processing),​ the IF bandwidth is set digitally with preprogrammed filter curves. ​
en/selectivity.txt · Zuletzt geändert: 2018/10/29 19:42 von mb