A few years ago the ham repeater operators decided to
add a sub tone to the repeaters input to control unwanted
repeater triggering. With this change owners of some older
excellent transceivers find themselves unable to use their
rigs on these repeaters. The later model rigs all have the
so called CTCSS option (Continuous Tone-Coded Squelch
System.) that allows the operator to set the sub tone used
on repeaters, and they operate as normal without any
difficulty.