ИСПОЛЬЗОВАНИЕ ФИЛЬТРОВ С ФИКСИРОВАННОЙ ПОЛОСОЙ ПРОПУСКАНИЯ ДЛЯ ПРОГРАММИРУЕМОЙ ПОЛОСЫ ПРОПУСКАНИЯ ПРОМЕЖУТОЧНОЙ ЧАСТОТЫ

摘要

A programmable IF bandwidth is achieved in either a transmitter or receiver using fixed bandwidth filters. A minimum of two IF frequencies are used. A fixed bandwidth filter that is equal to or greater than the desired IF bandwidth is used at each IF. The Local Oscillators (LO's) are tuned to frequency convert the desired signal to a frequency that is offset towards one bandedge of the fixed IF filters. A first mixer and LO relocates the desired signal to one end of a first fixed IF filter. A second mixer and LO relocates the filtered signal to the opposite end of a second IF filter. The desired bandwidth is obtained as the sum of the frequency offset of the desired signal from the nearest bandedge of the first IF filter and the frequency offset of the desired signal from the opposite bandedge of the second IF filter.