Scanners don't have a 'dual watch' capability such as you describe - however since there are innumerable older scanners out there that cover VHF air, you might have an older scanner sit on the ATC freq while you do other things with the 164. However...
Much depends on the antenna, how far away you are from the tower and the terrain that separates you. Generally a tower antenna drives the signal up and away (a crude approximation would be a flashlight shining towards a ceiling), so it's not always easy to hear tower comms when you are further away - say no more than a couple of miles or so.
The small antenna supplied with most handhelds is quite lossy at airband freqs, so a better antenna would likely be needed. Which antenna would be right for you also depends to some degree as whether you can mount it outdoors (which is best) or indoors, say in an attic (will reduce your range to some degree, but still better than the duckie). We have an antennas forum where that can be discussed in more detail, since that subject is OT here
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Last edited by ka3jjz; 06-20-2010 at 5:35 AM..