Normally a radio scanner is used to scan multiple frequencies as is the case with KISP. So, it will pick up the first available
transmission it comes across in its scanning program. Presently there is no way for you as the listener to choose which
frequency you want to listen to. Often the Tower/Approach/Departure personnel will identify themselves as, "Tower",
"Approach", "Departure". The approaching/departing aircraft will usually call, "Tower", "Approach", or "Departure",
which also is a big help. Some of the more extensive sites, such as KPHL, KBOS, have a number of scanners and can
provide separate feeds for Tower, Approach and Departure.
Enjoy listening.