Frequency control at your club
I like our system as there is no parts that can "walk away". There's two large sheets of plexiglass. They are about 3 feet tall and about 1/4 inch wider than 2 AMA cards the long way. Between the two sheets of plexi there is a 1/4 x 1/4 spacer that makes a gridwork just the right size that fits AMA cards. Glued to the back of both sheets are the frequency numbers so that you can see them through the plexiglass. When someone is using a frequency they put their card in the slot. Very simple.