circuit as described thus far provides improved and reliable operation for frequency shift keyed signals my circuit actually provides two receiver paths one path is through the even numbered circuit elements 16 18 20 22 24 26 and the other path is through the odd numbered circuit elements 17 19 21 23 25 27 these two paths provide improved reliability and signal to noise ratio since any noise signals which may be present are more randomly distributed through my circuit and persons skilled in the art will appreciate the various logic functions which can be derived from my circuit particularly that part shown in fig1 b for example for a guard signal only the logic 0 from the threshold circuit 26 and the logic 0 from the inverter 29 may be applied to a nor gate which will produce a logic 1 if a guard signal is present and no trip signal is present other arrangements can be used under more adverse conditions the lower portion of my receiver that is the parts indicated by reference numerals followed by a prime suffix may be used in addition to the upper portion the operation of this lower portion of my receiver is substantially identical to the operation of the upper portion.