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Re: Topband: Interaction on shunt fed tower with 1/2 sloper?

To: Mike & Coreen Smith <ve9aa@nbnet.nb.ca>
Subject: Re: Topband: Interaction on shunt fed tower with 1/2 sloper?
From: Ken Brown <ken.d.brown@hawaiiantel.net>
Reply-to: ken.d.brown@hawaiiantel.net
Date: Thu, 02 Oct 2008 20:57:20 -1000
List-post: <topband@contesting.com">mailto:topband@contesting.com>
> If I take down 
> the sloper ; then I will have no A-B comparison any more?!
>
>
>   
Hi Mike,

Yes the sloper does give you something to compare to, and you can call 
it an A-B comparison. It is important to remember that the A of the 
sloper and the B of the tower is not the same as either one would be if 
the other one was not there. In other words, since they are so close 
together they are bound to interact. If the sloper was far away, 
supported by a different tower or a tree, you could use it as a 
"constant" reference. Then as you tried different things with your shunt 
fed vertical, you could go back to the sloper as a reference for 
comparison. As close as they are, when you make changes to the shunt fed 
vertical it changes how the sloper works, and the sloper affects how the 
shunt fed vertical works, so they are not working independently. The 
tower may be acting as a parasitic reflector or director for the sloper, 
or the sloper may be doing the same, or perhaps the opposite, for the 
tower. One feed (the sloper for instance) may favor one direction and 
the other feed (the shunt fed tower) may favor the opposite direction. 
That could explain the sloper working better on a lot of signals. The 
two are most likely not operating as two separate antennas, but rather 
as two different ways of feeding a multi-element array.

I understand your hesitancy to remove the sloper, however it may be 
confusing the issue if you think of it as a reference.

If you were to have a three position switch on the shunt feed, one 
position open circuit, one position straight to ground, and one position 
grounded with the capacitor in series, you would probably get three 
different signal strengths from signals on the sloper.

Ken N6KB

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