Trust me, they can hear pretty much everything if they want
People should know and realize that Intercepting communications of any format is trivial to people who have the right training, like what they do at Corry Station. Any Army 35S or 35P, Navy CTR or CTI, or Air Force 1N2X1 or 1N4X1 can breach any type of perceived "security" extremely quickly. These people are extremely good at what they do.
The jobs that actually do interception and the units that do interception can see, hear, and interpret pretty much any signal you emanate, from a 800Mhz "walkie talkie" type radio like the Taliban and Haqqani use (the Police in North America and Europe usually use the same infrastructure, Motorola and Harris make a killing in that market) to a very high end SHF satellite.
They can also intercept every packet your computer, phone, and router emanate. They usually listen upstream, as was evidenced in what AT&T was doing at 611 Folsom Street in San Francisco in Room 641A.
My point here is that you are not secure, if they want to listen to you they can and they will.
They hear SW like the numbers stations and such but thats mostly HUMINT craziness and DIA and CIA are interested in that stuff. Usually they're orders for operatives. Russians do it all over the place, the Chinese do it at all of the National Labs here in the US (the Yosimite Sam signal's transmitted just South of Albuquerque, we do it in the Middle East from Cyprus.
The point is, don't think they can't listen to you if they want to. Don't make them want to, and you're straight. And if you work with them at any point in your life, assume they're always listening to you.