the complement of 34 b 34 signal 34 e 34 only changes on the rising edge of 34 c 34 and its value takes on the value of 34 a 34 at that instant signal 34 e 34 also represents the decoded manchester data output in order to decode data that has been encoded in bi phase mark or space additional elements 114 and 118 are provided encoded data stream 34 a 34 is applied to exclusive or gate 114 which generates intermediate output 34 d 34 the inverse output signal 34 f 34 from flip flop 116 is also applied to exclusive or gate 114 when 34 f 34 is low 34 d 34 is equal to 34 a 34 when 34 f 34 is high 34 d 34 is equal to the complement of 34 a 34 d type flip flop 118 generates the bi phase mark data output 34 g 34 when intermediate signal 34 d 34 is applied to the 34 d 34 input of d type flip flop 118 and clock signal 34 c 34 is applied to the clock input of d type flip flop 118 34 g 34 only changes on the rising edge of 34 c 34 and takes on the value of 34 d 34 at that instant bi phase space data can be recovered at output 34 q 34 of d type flip flop 118 delay line 110 can be formed by using any suitable distributed or lumped delay element for bi phase encoded data the ideal sample point is 3 4 of a bit period from the reference edge so in this particular embodiment the delay line has been preferably choosen.