Short answer on Tx freq issues in the US.

Many Eruo freqs are illegal, depending on how you read the laws (or not, depending on how you read them.)

Im not the FCC, and my concern is with two Txs on the same freq, not what freq that is. If the FCC comes down on us and has an officer there, they can enforce it. Its not our job to worry about a micro-watt transmitter operating on a freq that no one outside our event is using. Its not like your interfearing with air traffic control...

If a bunch of guys come over with 40 MHz Txs, my greatest concern would be making more clips for the respectvie freqs. (we do run tight freq control as to if your Tx is on when that particular channel hasnt been checked out - thats a safety issue, nothing more.)