That is because it is patented by Motorola. Please refer to US Patent #3,584,304
US Patent #3,628,058 also describes the squelch circuit used in the Micor and even gives a schematic for the M6709. On Tue, Nov 10, 2009 at 4:15 PM, JOHN MACKEY <jmac...@usa.net> wrote: > It's been since the late 1950's that reverse burst has been around for > PL tones. So for over 50 years the ham manufacturers haven't gotten > on board yet.
