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