Topband: EZNEC Shunt Feed Model Gain

[Bob Kupps]

Hi George
I have been modeling a 3 el vertical yagi over the rice paddy ground we have here in HS land and after tweaking everything got around 9 dBi of forward gain. After modeling a gamma match for the central tower the gain dropped ~ 3 dB without affecting the pattern. When I then modeled a single shunt fed tower vertical the gain also dropped by a similar amount. I think it's a modeling artifact and my pal back in the States WX7G agrees.
73 and good luck
Bob N6BK/HS0ZIA

--- On Tue, 8/18/09, k8gg at voyager.net <k8gg at voyager.net> wrote:

From: k8gg at voyager.net <k8gg at voyager.net>
Subject: Topband: EZNEC Shunt Feed Model Gain
To: topband at contesting.com
Date: Tuesday, August 18, 2009, 9:42 PM




Fellow Topbanders:

I made a model of a shunt fed Rohn 45G
tower with a 2 element short 40 meter beam on top.  I used 78 feet of
tower plus 12 feet of 2.375 inch diameter mast plus the actual dimensions
of the boom and elements for the beam. 
When I model it as
series fed at the base, all the data looks good, with a gain of about 1.5
dbi and a self resonance below 1600 KHz.
When I model it as a shunt
fed tower, base grounded, with 50 feet of 1.6 inch OD pipe about 27 inches
from the center of the tower as the shunt feed rod, the gain drops to
about 0 (zero) dbi.  The radiation pattern, etc. stays the same.
Is this a fault of EZNEC4, or does the shunt feed truely reduce the gain
of the antenna?

Thanks for your thoughts, 
73,    George  


_______________________________________________
Topband mailing list
Topband at contesting.com
http://lists.contesting.com/mailman/listinfo/topband


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com