Btw, I don't think it only works with a small number of transmitters. In the UK they has been taxing TV watching, and managed to have a huge fleet of specially equipped vans cruising streets, identifying where are TV sets (and it's harder task then scanning for transmissions), and checking addresses against national registry. Nowadays, I suppose methods are different due to internet broadcasting, but it seems they are still capable of taking pennies for it quite successfully. FWIW, state officials love massive budget disbursements, creation, and expanding of departments, and they can use modern technologies for large-scale operations too.