This is something I've always wondered, and i think i know the answer before i ask the question, but just wanted some verification. For all of the different frequencies i see listed for an ARTCC are at different locations, and transmit from that area. Example the Alexandria freq of the Minneapolis ARTCC, i can hear ground and plane, so its obviously transmitting from that area. However my question is, and I'm assuming this to be true, are all of these different locations that transmit originate from one location, IE MSP Center in Minneapolis. And if so how are they connected to the transmitter location. Also at these transmitter locations, is there a radar at that location as well, or is the whole ARTCC covered by one radar, though I'd think that is a large area to cover with one radar. Also are most of these transmitting sites located at airports, or just random locations? I hope this makes sense, and sorry it got so long.