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[TowerTalk] Beverage f/b

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Subject: [TowerTalk] Beverage f/b
From: W8JI@contesting.com (Tom Rauch)
Date: Mon, 22 Oct 2001 11:28:12 -0400
> All 7 of them don't seem to show the directivity on 160/80 that they
> did last winter.  

Look at the ground connections. A single driven rod is almost never 
enough.
 
> Two are two wire beverages (one of the pair unterminated, the other
> terminated to ground) and three are single wire with resistive
> terminations.  All 7 seem to suffer from the same directivity loss.

The type of two-wire Beverage having one wire directly grounded 
has less directivity and F/B than one with proper transformers.

Also, be sure the feedlines are NOT grounded to the same ground 
as the Beverage, and whatever you do....do NOT run a wire under 
the Beverage like some Handbooks unwisely suggest. Beverages 
depend on ground loss below the Beverage in order to work 
properly!
 
> The one thing I can't readily check is the ground side performance.

Sure you can.

Connect the Autek to the feedpoint through the transformer, and 
lay a 60-80 feet of wire out on the ground away from the Beverage. 

Connect it to the Beverage ground, and see if SWR or impedance 
changes more than a few percent. If it does, you have poor 
grounds. 

A single six-foot 3/4" copper pipe here in my reasonable 
conductivity clay soil has about 100 ohms of RF resistance on 160-
meters. In many QTH's, I've seen a range of 60-150 ohms or so 
depending on moisture.

If I happen to connect the shield of the coax directly or indirectly to 
the Beverage  ground, the feedline shield significantly couples 
signals into the Beverage and this noticeably reduces directivity. 
The exception is if I have six or more radials at the feedpoint of the 
Beverage.

That's why we should always isolate the coax shield from the 
Beverage ground. 

Also, keep 'em away from transmit antennas and towers. 

> I'm wondering if it is just too early in the season to expect them to
> perform or because they are run under a canopy of trees which still
> have leaves.  

I have never seen a difference at all from leaves, and I've had 
hundreds of Beverages over the years. At this QTH, I have antenna 
through dense woods with 100 foot tall trees and through open 
pastures. Signal levels and F/B are unaffected (as near as I can 
tell) by trees and leaves, although I do make sure leaves are not 
laying against the antennas as much as I can (but even that seems 
to have no noticeable effect).

I definitely can notice open terminations, and broken antennas!

73, Tom W8JI
W8JI@contesting.com 

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