TopBand: receiving antennas
Mon, 16 Sep 1996 10:34:33 -0400
In a message dated 96-09-16 09:44:04 EDT, you write:
>The current thread of EWE's, Beverages and other receiving antennes has
>neglected one important point. If you have the room to use a Beverage, do
>it. If you have to compromise, the loop, EWE's or shortened rx antennas are
>a compromise. They are not going to be an optimal antenna. (I know this is a
>debatable statement. However, when in doubt, I favor Beverages.)
Actually a Beverage (or any other long wire array) supplies among the lowest
directivity per acre of space of any array. The saving grace is that they are
simple and easy to build, and more forgiving of mistakes. Like any longwire
array, the problem is all the sidelobes and the inability to maintain current
a long distance out on the wire. The "far end" rapidly disappears from the
system due to ground loss and radiation.
The small verticals I used were untuned ten foot probes. There is no reason
to "load" the elements, as a matter of fact loading actually hurts
performance because the system becomes more phase-frequency dependent.
Four verticals spaced 300 ft broadside and 70 ft endfire worked on 80 and
160, and was superior to any of the dozen Beverages or phased combos of the
Beverages I had.
Receiving antennas aren't magic, they function by placing nulls in the
direction of noise sources. And a 5/8 wl broadside 1/8 wl endfire combo
provides a lot of directivity with a clean pattern.
A 250 ft long Beverage with proper inductive loads spaced every 1/8 wl and
proper termination (much higher than the normal 500 ohms) actually has better
directivity and S/N than a 500 ft long unloaded antenna.
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