Thanks for the replies - very useful - so it is also to do with the hardware within the radio itself!
A kind-of related question on radios:
I take it that you do not need to show a licence when buying a transceiver from a pilot shop or on the web? - I've never tried.
Have anyone heard of any ATC transmissions being intrupted by someone using a transciever on the ground near airports - either on purpose or through ignorance.
I know from reading the Trevor Thom's Radiotelephony book that ATC can move to an alternative frequency - but that obviously depends on informing the aircraft of that frequency. What would happen in this case? - worst case scenario using light signals
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