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From: bcsaic!carroll@cs.washington.edu (Jeff Carroll)
Newsgroups: comp.dcom.telecom
Subject: Re: Questions About the GTE Airfone
Message-ID: <15520@accuvax.nwu.edu>
Date: 18 Dec 90 20:09:51 GMT
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X-Telecom-Digest: Volume 10, Issue 891, Message 4 of 7


In article <15300@accuvax.nwu.edu> rees@citi.umich.edu (Jim Rees)
writes:

>In article <15223@accuvax.nwu.edu>,  seanp%undrground@amix.
>commodore.com (Sean) writes:

>>The transmitter section of the setup is IMPRESSIVE. Everyone could
>>concievably use thier phone at the same time, as there are 400
>>channels available for use.

>I doubt very much that the airplane is able to transmit on 400
>channels, or even 56 channels, at once.

	I would also doubt that you could operate 400, or even 56,
independent radio channels from the same bird. Even doing 25 (as we
have on AWACS) results in horrendous self-jamming and elaborate
frequency allocation software, not to mention hundreds if not
thousands of pounds of antenna couplers.

	On the other hand, a recent conversation with the manager
responsible for integrating the equivalent of AirFone into our next
generation airplane left me with the impression that there was quite a
big chunk of bandwidth required. One obvious solution would be an
onboard DS1 mux which performs upconversion at its output to an IF
frequency of the UHF set (most likely 70 MHz). I don't know whether
such a beast exists today, but I doubt that that's what is used in
most AirFone installations (i.e. one phone in the back of the plane).


Jeff Carroll
carroll@atc.boeing.com