An improved decoder for providing a decoder output signal when a tone signal contains {HEAD ~ frequencies} that are sequentially within {TAIL ~ a predetermined passband} surrounding first and second detection frequencies f1, f2 
An improved decoder for providing a decoder output signal when a tone signal contains { HEAD ~ frequencies } that are sequentially within { TAIL ~ a predetermined passband } surrounding first and second detection frequencies f1 , f2
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH