Hi Harvey,
The Moni button opens the squelch. Hold it down and you will hear the
rushing sound indicative of open squelch. Release it and you go back into
squelched mode. Just a bit of added information, when you hit the function
key (the a key in the upper right corner of the keypad) and then hit the
moni button you can turn the 20DB attenuator on and off. I hope this helps.
Dave Marthouse N2AAM