Device for demodulating signals modulated by frequency-shift keying

DETAILED DESCRIPTION What is claimed is: 1.
A device for demodulating signals modulated by frequency shift, said signals being constituted by sequences of n oscillation trains, n being an integer greater than 1, in which each train has one or the other of two given frequencies F.
sub.
1 and F.
sub.
2 and a given time-duration .
tau.
, and the sequences being issued from a base sequence of n oscillation trains by circular permutations of the successive values of frequency of the n trains, said sequences being representative of a binary code with n coded sequences having circular permutations, said demodulating device being provided with an input for receiving said coded sequences, an output and first and second filtering channels matched with one of the sequences of n oscillation trains which is called tuning sequence, said filtering channels having respective input channels coupled to the input of said device and a common output channel delivering a response signal for a received sequence, said input channels being time-delayed for producing an increase in the transit time by n.
tau.
in said first filtering channel with respect to the transit time in the second filtering channel, said demodulating device further comprising a detection device having an input coupled to the common output of the filtering channels and an output which is the output of said demodulating device, for detecting in the response signal an instant at which said response signal corresponds to said tuning sequence, said instant being characteristic of said received sequence.
2.
A demodulating device as claimed in claim 1 wherein said input channels comprise respective filter having a pulse response in the form of a train of amplitude modulated oscillations having a frequency ##EQU13## and a duration 2.
tau.
, said filter having respective inputs connected to the input of the device and respective outputs, the first input channel further comprising a delay device, with a delay equal to n.
tau.
, having an input coupled to the output of the first filter and an output, the output of said second filter and the output of said delay device being coupled to a common output of said input channels which is coupled to said common output channel