>Hi all,
>
>I live in the Boston area and I like to listen to VHF aircraft comms.
>I noticed something odd recently, though: it appears that Boston
>Approach is using duplex comms. I hear only the ground to air side of
>the communication on 124.4MHz and then an immediate reply from the
>aircraft on 133.0 MHz. I found this by chance because I had heard
>traffic on both of those frequencies while scanning around and finally
>started switching between them.
>
>I had thought that the VHF air band was simplex. A quick web search
>didn't yield any answers.
>
>Anyone know what is going on here?
>

Some airports have multiple frequencies, one for each sector/purpose. 
Sometimes they will transmit on all frequencies. The aircraft will 
only transmit on one frequency.  Based on your location, you may be 
able to only hear the ground frequency for another sector, not the 
one the aircraft is in (since it is at a high altitude, you can of 
course hear the plane from a further distance).


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Chris Smolinski
Black Cat Systems
http://www.blackcatsystems.com
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