Just perusing the ARRL letter on rec.radio.info and the lead story was
very interesting. It's about the ARRL objecting to the use of some 70cm
frequencies for a commercial event.

This paragraph in particular caught my eye:

"The ARRL called the Miller Motorsports Park choice of
channels 'completely inappropriate. The radio amateurs who
are licensed to use these frequencies are under no obligation
to either tolerate interference or to cease their own operation,
regardless of the interference that might be suffered at any
time' by Miller Motorsports."

Just goes to show how things are different in the US to here in the UK.
Over here we are only secondary users of the 70cm band (the primary user
of just about everything above 2m is the Ministry of Defence) and so we
have to put up with anything and everything, including car alarm keyfobs
on 433.92 MHz as an example. We also only get 430-440 MHz rather than your
420-450.

Even in the 2m band (144-146 not 144-148 MHz..!), of which we are primary
users,we cannot claim protection from interference.

Ah well..!

73 Ivor G6URP