Quadrature multiplying four-channel demodulator
AssigneeQuadracast Systems, Inc.
InventorLouis Dorren
Life of this patent
Estimating the term…
Abstract
A decoder is provided for a FM radio four-channel system having the usual 19 kHz pilot signal, a first subcarrier at 38 kHz, a second subcarrier in quadrature therewith, and another subcarrier at 76 kHz. The decoder of the present invention is a time division system wherein the 19 kHz pilot signal is doubled and the phase shifted 90.degree.. This produces sine and cosine 38 kHz signals to provide a first pair of outputs, and each of these signals is inverted to provide a second pair of outputs. By properly adding the four outputs thus derived, switching signals are provided to decode the four channel information.
Claims5
A decoder for composite FM signal wherein the composite signal has a main channel having first, second, third and fourth bits of information thereon, a pilot signal removed from said main channel, a first subchannel having a frequency twice that of said pilot signal having two carriers in quadrature thereon, namely, a sine carrier containing plus first plus second minus third minus fourth information and a cosine carrier containing plus first minus second minus third plus fourth information thereon and a second subchannel at a frequency twice that of said first subchannel containing plus first minus second plus third minus fourth information thereon, wherein the improvement consists of a means of demodulating the above-described four channel composite signal, such means comprising in combination:
- a. means for extracting said pilot signal;
- b. means for doubling said pilot signal to yield a first switching signal representing the sine carrier of the first subchannel;
- c. means for inverting said first signal to provide a second switching signal 180.degree. out of phase with said first switching signal;
- d. means for doubling and shifting the phase of said pilot signal to provide a third switching signal 90.degree. out of phase with said first switching signal representing the cosine carrier of said first subchannel;
- e. means for inverting said third signal to provide a fourth switching signal 180.degree. out of phase with said third switching signal;
- f. first, second, third and fourth AND gates,
- g. four switches, each switch being actuated by one of said AND gates, said switches being connected to switch said composite signal to four outputs;
- h. means for feeding the first and fourth switching signals to the first AND gate;
- i. means for feeding the first and third switching signals to the second AND gate;
- j. means for feeding the second and third switching signals to the third AND gate;
- k. means for feeding the second and fourth switching signals to the fourth AND gate whereby,
- l. the output of each of said switches represents one of said bits of information.
Dependencies are inferred from the claim text.