It's very hard to make sure that the signal extends exactly to the perimeter of the prison. If your jamming signal is weaker, some corners of the prison will ha

It's very hard to make sure that the signal extends exactly to the perimeter of the prison. If your jamming signal is weaker, some corners of the prison will have reception. If it's stronger, you are illegally blocking the signal outside your prison. Add to that that signal strength changes with weather, and you have two solutions: either lots of expensive equipment or lots of buffer land owned by the prison. Both are expensive.