Message-ID: <000f01c0e19a$1b3141c0$a0ca0041@mshome.net>
From: "Robert Smiley" <robsmiley@home.com>
To: <lancair.list@olsusa.com>
References: <005201c0e17a$8b051640$84588ec6@user>
Subject: Re: LIV nav reception
Date: Sun, 20 May 2001 20:02:36 -0600
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There are two problems using two antennas and a splitter in reverse used as
a combiner.

First. all splitters and/or combiners lose signal strength resulting from
the internal circuitry.  This is a fact of physics and can be easily
measured and considered in design.  ie a two way tv splitter loses 3.5 db
signal loss. A three way splitter  is nothing more than three two way
splitters combined in a triad.  Thus the loss is 3.5  plus 3.5 or 7 db
total.  In the two way scenario you would want the antenna to produce more
than 3.5 db in order to provide a gain in signal strength.

The second problem is antenna phasing  which are combined in an array ie.
the signal may reach the antenna at different times thus the signal when
combined may be slightly or grossly out of phase thus degrading the signal.
This can be overcome with  precise length cables between antennas.

Third It can only be done on stationary fixed situations.  Since the plane
is moving through the air and the antennas cannot be equi -distant from a
tansmitter you have  a situation that cannot be solved.

Example,  I owned and operated a cable tv system.  Weak tv signals could be
amplified by an array of up to four tv roof top antennas cut to a specific
frequency coupled with three two way combiners.  The jumpers between the
antennas and combiners had to be very precisely cut and the image viewed
through an oscilloscope and tv to see if the multiple images were in phase.
Out of phase images were visualized as leading or trailing ghosts or
multiple images.  This is the same image you would see from multi path
situations where the single source signal was received by a direct path from
the transmitter and other reflected signal paths from buildings, water
surfaces, aircraft bounces etc.  The fix on the array was to minutely vary
the jumpers between the antenna and splitters to vary the time length to
place the images in phase thus overlapping the images in time and space.

With respect to audio signals; multipath signals may be less sensitive.  I
would be interested how successful your idea would work in a mobile moving
audio only application.  As for video it definitely will not work.

Bob Smiley
N94RJ

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