David Casey wrote:
Do aircraft and folks on the ground talk to each other on 2 different
frequencies? I seem to hear the ground controllers and the actual pilot on
2 separate frequencies talking to each other.

Also, there seem to be a large number of frequencies to listen to regarding
aircraft around here, but which should I concentrate on? I'm just
interested in listening to the planes and the ground controllers and such.

Dave

Here is what you're hearing which probably gave the impression
of ATC and the aircraft using two different freq.

This is common at night time where there is less
traffic and less controllers on duty. Since you didn't mention any
frequencies I'll use this as an example, this was an actually example of
someone with the same question who lives in Boston, MA. Lets say
you're hearing the ground controller (ATC) on 124.4 but you're hearing
the aircraft answering on 118.25. One controller is probably
controlling three different sectors. The controller in our example is
keying up
the mike and his voice is being broadcast on 120.6, 118.25, 133.0, and
124.4 at the same time. The antenna site for 124.4 is probably near you
as that is the only one you are hearing. The other three antenna sites
are located near the center of the North sector, West sector, and South
sector, too far away from you to hear. So, you might hear Boston say
"Delta 411 decend to one four thousand" on 124.4000. However it was
also broadcast on the three other freqs but you were just too far away
from those antennas to hear it. But now you can hear Delta 411 on
118.25 say "out of 210 for one four thousand Delta 411". You heard the
Deltas reply because he was much higher and in line of site with your
radio. This would give the impression of Duplex but in reality Delta
hear ATC on 118.25.

If you tell us where you're located someone here might be able to help
you with local ATC freqs for your area.

George
http://www.MilAirComms.com