On the bottom edge of the radio just to the right of the tuning knob is a row of
buttons. The second from the left sets your tone and once you've set that hold
the left button in while someone is talking until there's a beep and the
subaudible tone will be set.
Tom
Tom Brennan KD5VIJ, CCC-A/SLP
web page http://titan.sfasu.edu/~g_brennantg/sonicpage.html