Re: Ethers, Copper, Fiber, Microwaves, Etc.


Rob Horn (adelie!infinet!rhorn@XN.LL.MIT.EDU)
12 Dec 87 18:55:45 GMT


I think that these systems are operating in the 23 GHz band. The
frequencies between 21.2 and 23.6 GHz are set aside for commercial
short-haul communications. This band has 2.4 GHz available, which is
a whole lot. The equipment also tends to be relatively cheap,
typically under $50K.

The antennas that I have seen have been 2-3 foot diameter, giving
antenna beam widths of a few degrees. This is more suitcase size
than briefcase size. The wider beam width and small antenna make
these easy to install. The reliable range at 23 GHz is at most a
few miles. The attenuation in air is not too bad, but fog and
rain cause significant problems. You have to expect dropouts
during heavy rains. The greater the distance, the more you need
to worry about these things.

Short-haul microwave is a good complement to fiber optic and
copper wiring. The installation cost is much lower than physical
cable, provided you have line of site between the two ends. FCC
licensing is required but usually easy to get. The frequency
band is huge, not too heavily used (yet), and the attenuation is
such that you can ignore sites that are many miles away. You
have to put up with dropouts during heavy rains, so for
applications that must work during bad weather they are a bad
choice. (Dropouts act like a very overloaded gateway. Traffic
can still pass occasionally but lots of packets get lost.)

--
				Rob  Horn
	UUCP:	...harvard!adelie!infinet!rhorn
	Snail:	Infinet,  40 High St., North Andover, MA
	(Note: harvard!infinet path is in maps but not working yet)



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