>the US rules are that you can use digital protocols but you must publish the specs so anyone can, in principle, decode the signal.
This restriction does not appear to actually be enforced, eg, if I recall correctly the VARA HF/FM modes do not have published specs anywhere near sufficient to decode them, to the point where there are projects trying to reverse engineer them.
This restriction does not appear to actually be enforced, eg, if I recall correctly the VARA HF/FM modes do not have published specs anywhere near sufficient to decode them, to the point where there are projects trying to reverse engineer them.