[BC] Re: High Gain vs Low Gain Antennas

[Glen Kippel]

On Thu, Feb 19, 2009 at 8:42 AM, Richard Fry <rfry at adams.net> wrote:

> For all practical purposes a high-gain, omni antenna with beam tilt can
> radiate close to the same ERP in the elevation sector serving its useful
> coverage area as if a low gain, or even an isotropic radiator was used.
> That radiation doesn't go over the heads of the receivers it is intended to
> serve, or need to serve them mostly with scatter.
>

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What really matters is the field strength at the receiver.  KWXY could, I
suppose, reach its 50-kW ERP by running 100 kW into one bay.  (Ignoring line
losses.)  Anybody want to pay that power bill?  LOL.  Or 50 kW into two
bays.  But wait a minute -- we would be putting over half of that power over
the heads of the people out there.  And a significant amount down at the
ground within a couple of miles, where there are no living creatures except
a few rattlesnakes, chuckwalla lizards, jackrabbits and an occasional
coyote.  Since received field strength is a function of power times antenna
gain, it is much more efficient to use the latter.  The hard part is to come
up with an appropriate balance between the two.  Also, because of
inverse-square law, proximity of the transmitting system to the receiving
system is important, too.  If you are serving a market that is surrounded by
a hundred miles of nothing, it doesn't make sense to put a signal out there
at the expense of the populated area.