99% of the Secret Service comms are encrypted. You MIGHT hear them talk to AF1 as it is on the ramp, if you are very close...last time they were in Dallas it was on Sierra. What you usually here is increased talk on the local stuff, especially any little used tac or swat channels. What's actually cool is listening to the airport control tower handle AF1 inbound and outbound...start listening 20 or so minutes before landing, and hear the airspace being cleared of any traffic, planes on the ground being stopped, etc. Of course it is AF1 ONLY if the POTUS is onboard, so when they called ground control before he returned it was as SAM 2001...it was there I heard them ask the tower for an opposite flow departure and they flew right over my house...shook the rafters. SS may not be able to be heard, but a lot of stuff around a visit is. Also try the local media freq...they go into hyperdrive during a visit.
