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The LiTZ (long tone zero) has been proposed as a way to programmatically identify emergency transmissions. But do any radios actually recognize it? Many can send it; but at the very least I'd want a radio to stop scanning and turn off any CTCSS/DCS squelch upon receiving a long enough zero DTMF tone. I have seen online descriptions of how to build a circuit that will do various things when it detects an at least 3 second long DTMF zero, but I have been unable to find a radio that has the detection built-in.

I would think that considering some of the paging modes in my Yaesu FT-530 -- which appears to have been manufactured before LiTZ was first proposed --, that it would be easy for manufacturers to design LiTZ detection: when scanning if DTMF zero detected pause on that frequency to see if the DTMF zero continues for a long enough duration. If it stops short, continue scanning; if long enough, open the squelch.

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