[BC] MW Space Diversity Reception

[Mike McCarthy]

I didn't infer cross pol'g would be necessary by design.  Only that it 
happens....

MM

At 08:57 AM 7/2/2006 -0500, Stanley Adams wrote
>You do not put your diversity on the cross pol (i.e. H if the main is on V).
>That is an auto 30 dB loss and is of no value.
>You tie you lines together through either proper equipment designed for
>diversity reception by the manufacturer (i.e. level switch,
>active combiner, and the like).  Active combining with properly delay
>aligned (between the active and main antennas--we call it DADE) can actually
>add about 6dB to the main down converter level.  But if you do not have
>those means the only other possibility that I can think of is a 3dB
>splitter. A level switch will also require some form of DADE'ing either of
>the old manual type by adding extra coax to the
>diversity line to bring it up to the difference in the length of the main to
>diversity antennas.  Or the auto type where you turn a screw on the
>manufacturers receiver that has already accounted for delay lines.
>
>You loose three dB on the main active path, or the backup for all that
>matter.  However you keep up a path and a low path is better than a no path.
>But in severe temperature inversions as we have this time of year, both
>paths can just lay down and die for a while.
>There is nothing 100%.  While doing the initial design engineering of the
>path you will want at least a 45 dB fade margin between
>where the main normal path level resides and where the 1 x 10-6 or 10-8
>level occurs if we talk digital, if analogue you will want
>to switch at about -40 or so if the squelch is about a -60 or -65.  This
>should help you keep up in the really high 99.9% area.
>99.0 is worthless for a station like WLS or some of the other big (or
>smaller) ones; it is the decimal side that really counts.
>
>Use of the Bell MW Design manual is good on this as well as the old Air
>Force MW set of manuals.  For the design engineers of Marti and others this
>is a cake walk.  Andrew Corp has some downloadable software for path calc's
>as do other of the manufacturer's sites.
>
>Stan Adams
>Memphus
>
>
>
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