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From: Paul.Schleck@iugate.unomaha.edu (Paul Schleck)
Newsgroups: comp.dcom.telecom
Subject: Re: Cellular Phone Signal Propagation Characteristics?
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Date: 5 Jan 91 04:35:40 GMT
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X-Telecom-Digest: Volume 11, Issue 7, Message 6 of 13


Cellular phone operates at about 900-950 Mhz.  This may be properly
termed microwave.  Propogation of waves at this frequency are
essentially line of sight.  They are so energetic that they (usually)
cannot be bent by the atmosphere, so hence no significant multi-hop,
over the horizon propogation.  Under conditions of tropospheric
inversion, i.e. higher layers of the atmosphere warmer than lower
ones, a phenomenon known as "ducting" may occurr, under which the
waves are made to conform to the curve of the earth.  Propogation
under ducting conditions may be up to several hundred miles.

It is true that usually microwave RF does not travel very far for a
number of reasons.  For one, it does not follow the curve of the earth
under normal circumstances.  For another, its short wavelenth means
that it is rapidly attenuated by foliage, walls, humid air, etc.

What is the height difference between where you were and the cell
sites back in CA?  If there was enough of a height difference to cause
an obstruction-free straight line path, that may be another
explanation.
 
One of the reasons that cellular technology works is "capture effect."
What that means is that only the strongest signal being received is
actually demodulated in an FM signal.  The reasons are beyond the
scope of this discussion group.  Also, cellular systems use a voting
system to insure that only the cell with the strongest signal is used
for the phone conversation.
 
In short, it is the combined reasons of line-of-sight paths, capture
effect, and cell voting that cellular systems work.
 
For another propogation anecdote, a friend of mine accessed the
Washington DC cell system from the middle of New Jersy under
conditions of tropospheric ducting, so it certainly can be done.  I
wonder what the phone company or the FCC thinks of these "long
distance" calls?


Paul W. Schleck, KD3FU

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