Some time ago I had an Omaha surveillance helo in contact with a ground unit instructing him on how to receive the video from the helo. He instructed the ground unit to make sure his receiver is set for 2285.00 MHz. This was heard in Massachusetts, so the helo could have been in any of the surrounding states, as he told the ground unit he was at 4,000' and the ground unit was not heard.
DEA does the same thing in every major metro area. The video feed is unencrypted is you have the means to intercept it but you would need to be in range typically within a few miles of the aircraft. They are typically using unmarked Eurocopters.
USMS also has fixed wing aircraft with FLIR/video but I dont know if they are doing down link. I saw one of their Cessna aircraft in Kansas City and it didnt appear to have an antenna for doing video down link.
Also the national guard in almost every state has twin engine fixed wing aircraft available for narcotics surveillance. Most have video down link capability. I know Florida has 2 Saab's used for this purpose but they do travel outside of FL.
I logged a civil ISR aircraft during NATO exercises this fall using video downlinks listed below...worth noting since they are often "rented" by government agencies when federal aircraft aren't available.
1820.0 - low power video and metadata
1840.0 - high power video