[TowerTalk] Unique Shunt Feed

[David Gilbert]

I don't see the link, but I assume this is it:

http://www.vias.org/radioanteng/radio_antenna_engineering_02_03_04.html

Another way of thinking of a shunt fed tower is that it is a folded 
monopole (half of a folded dipole) using conductors of different 
diameter, except with a single conductor extension (i.e., a "stinger") 
on top.

Anyway you want to look at it, the physics of operation of a shunt fed 
tower is simply based upon transmission line concepts.  For example, a 
shorted transmission line less than 1/4 wavelength long is inductive, 
which is why a series capacitor is almost always used at the base.

73,
Dave   AB7E

p.s.   I've never tried it, but it seems we should be able to make a 
folded dipole out of coax (shorted at both ends) by feeding the center 
wire in the middle of the coax while maintaining continuity of the 
shield.   I suspect somebody has already done that ... with the shield 
doing the radiating.  I'm curious what the feedpoint impedance is.



On 9/16/2021 11:48 AM, Dennis W0JX via TowerTalk wrote:
> What you are asking about is not unique at all. In the broadcasting industry, it is called "Center Feed." I have intended to try this with my 80 foot shunt fed tower but I have reasoned not to mess up what is already working very well.
> The attractiveness of the "Center Feed" approach is that there would no longer be stand-offs getting in the way of other antenna components and it is easier to climb the tower. The negative part is that finding the right level to tap the tower is probably pure guess work and it is a bit harder to adjust when it is inside the tower. Perhaps an Omega Match approach would make it easier to do.
> Anyway, here is a link to an article about the "Center Feed." I believe a VE2 also tried this method but I don't remember the call sign:
> Radio Antenna Engineering - Shunt-fed Radiators
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> 73, Dennis W0JX
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> Radio Antenna Engineering - Shunt-fed Radiators
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> H. Lohninger
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