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From: riddle@hoss.unl.edu (Michael H. Riddle)
Newsgroups: comp.dcom.telecom
Subject: Re: Questions About the GTE Airfone
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Date: 20 Dec 90 11:16:13 GMT
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In <15520@accuvax.nwu.edu> bcsaic!carroll@cs.washington.edu (Jeff
Carroll) writes:

>	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).

When I flew on the SAC airborne, we had UHF mux with 15 channels, and it
was /old/ technology.  While I agree that 400 would be overkill, I'd think
standard telephone switch-sizing techniques would lower the anticipated
service requirements down considerably.  A designer might want to adjust
for projected load-mix, such as a business shuttle vs vacation charters.

Back in the old step-by-step telephone days, most installations only had
line-finders for 10-15% of the phones in service.  My guess is that for
airfones, something less than that would be adequate.  Ever had to wait
for dialtone on your regular phone?  It /does/ happen occasionally.


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