| 摘要 |
PCT No. PCT/SE83/00107 Sec. 371 Date Nov. 23, 1983 Sec. 102(e) Date Nov. 23, 1983 PCT Filed Mar. 25, 1983 PCT Pub. No. WO83/03732 PCT Pub. Date Oct. 27, 1983.An apparatus for identifying multi-frequency signals, the received signals being processed in selective receivers after having passed through a digital bandpass filter. The input signal to the receivers is multiplied at sampling times by a coefficient from each of two sets of coefficients. The first set is obtained by multiplying a sine function by a weighting function and the other by multiplying the same sine function phase-shifted pi /2 by the same weighting function. The product of multiplication is formed and squared individually for each one of the multiplications, and the squared results are summed to obtain a measure of the signal energy within the passband. The received signals are subjected to an absolute amount generation and digital filtering in two non-selective receivers the first of which is affected by the changes in the composite input signal level and controls the start of the calculations periods in the selective receivers, and the other generates a signal which is a measure of the envelope amplitude. A circuit forms a sum signal from all selective receivers and a comparison circuit compares the sum signal with a signal obtained by squaring the output signal from the second non-selective receiver. A logical circuit selects the greatest of the selective receivers' signals, a threshold circuit forms a threshold value which is proportional to said greatest signal, and a comparison circuit decides which of the remaining signals that is sufficiently great for indicating together with the greatest signal that a digital multifrequency signal has been received. |
