Path: utzoo!utgpu!watmath!att!rutgers!ucsd!tut.cis.ohio-state.edu!mailrus!ames!dftsrv!hq!illgen
From: illgen@hq.af.mil (Keneth..Illgen)
Newsgroups: comp.dcom.lans
Subject: Re: line-of-sight technology
Message-ID: <656@hq.af.mil>
Date: 13 Nov 89 13:06:03 GMT
References: <1989Nov9.175018.26644@hellgate.utah.edu>
Reply-To: illgen@hq.af.mil (Kenneth..Illgen)
Organization: Air Force HQ, Air Staff LAN, The Pentagon
Lines: 38

In article <1989Nov9.175018.26644@hellgate.utah.edu> haas@cs.utah.edu (Walt Haas) writes:

>We are considering options for a high-speed data link between our campus
>network and the computers in LDS Hospital, about three miles away.  There
>is a good clear line-of-sight between here and there, which would suggest
>that some sort of microwave or laser link would be useful.  However for
>a number of weeks each winter the air in between is filled with thick
>freezing fog.  Is anyone out there familiar off-hand with a good technology
>for dealing with this stuff?

     We presently use RF radio modems that support our LAN traffic for small
distances. However, I know the company that we deal with (ARLAN) makes a 
model of this radio modem that can travel, up to, six miles LOS. 

     Normally you MIGHT see problems at these frequencies (around 950MhZ)
with the fog and cold weather you mentioned but these modems use spread-
spectrum technology (SST) which basically stretches out the signal on 
transmit and crunches it back on the receive. At the distance you mentioned
weather really wouldn't pose a problem.  That's a pretty elementary
explaination of what it does but I haven't finished my first cup of
coffee yet.
     
     Anyway, SST provide for a reduction of noise interference; the kind
of interference you might see with your type of weather.

     If you're not too worried about budget then you might find a laser
system that is better but for the money you can't beat a good RF LOS with
SST. We use ARLAN's but there might be something better out there. If you
want more info on ARLANs drop me a line.


Kenneth Illgen
HQ Air Staff LAN
Pentagon, Washington, DC
(202) 695-5090
AUTOVON 224-6136

illgen@hq.af.mil