Side band

The frequency components of radio waves that occur on both sides of the carrier wave on the spectrum when modulating a carrier wave in wireless communication. They play a major role in signal transmission, with components higher than the frequency of the carrier wave called the upper sideband and components lower than the frequency of the carrier wave called the lower sideband. The width from the upper limit frequency of the upper sideband to the lower limit frequency of the lower sideband is called the occupied frequency bandwidth, and the allowable range is specified in detail in the Radio Law and Radio Equipment Regulations according to the type of radio station and the type of radio wave. The part that changes according to the change in the signal is the sideband, and exists in both amplitude modulation and frequency modulation. The width of the sideband in amplitude modulation is twice the highest frequency contained in the signal components, and in frequency modulation and phase modulation, it is approximately this number multiplied by the modulation index.

[Iwao Ishijima]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

無線通信において搬送波を変調するとき、スペクトラムの上で搬送波の両側に発生する電波の周波数成分。信号伝達のための主要な役割を担うもので、搬送波の周波数よりも高い成分を上(じょう)側波帯、低い成分を下(か)側波帯とよぶ。上側波帯の上限の周波数から下側波帯の下限の周波数までの幅を占有周波数帯幅というが、その許容範囲は電波法および無線設備規則に、無線局の種類、電波の型式に従って細目が定められている。信号の変化に応じて変化する部分が側波帯であって、振幅変調、周波数変調のいずれにも存在する。振幅変調の側波帯の広がりは信号成分に含まれているもっとも高い周波数の2倍になり、周波数変調や位相変調では、ほぼこの数字に変調指数を乗じた値となる。

［石島　巖］

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