Method and apparatus used was we shall now describe in a signal, 1984, combines the presence of two signals differant by the frequency, the amplitude and phase, and whose frequencies is present in a known serial

摘要

Method for detecting, in a combined digital signal, the presence of two signals differing in frequency, amplitude and phase and having frequencies occurring in a known series. Samples of the combined signal are multiplied by samples of only one derivative of each of the frequencies of the known series. This derivative is formed by the product of a modulating factor formed by the samples of a frequency which is the sum or the difference of (a) a fixed frequency of 2000 Hz and the frequency to be detected in the known series and (b) a factor allowing a filtering at the said fixed frequency and formed by the samples of the sine of the fixed frequency shifted by 45 DEG . These products are alternately stored in accumulators until after a certain time the presence of certain frequencies is deduced from the sum of the products in the accumulators by means of comparison.