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