Hi Mike,
I have a similar height mast (military AB-621) with a somewhat larger antenna
on top, 4 El. SteppIr. When K6SE was still alive I discussed shunt feeding it
with him. Earl thought it could be done, but probably would not be easy, nor
particularly effective. It would do a good job on 80.
Due to a nasty storm, I had to erect something quickly for 160. It's similar to
you tee. My wire was parallel to the mast and the tophat wire was almost 150'
long. Very slight slope to it due to the trees supporting the ends of the wire.
It worked VERY well.
All the reading and discussions I have over the preceding 6 years suggest that
anything above the first capacitance hat/wire provides little or now benefit. I
think there have been articles through the years in magazines like Ham Radio,
QST and QEX that have explored this topic.
By the way, you had a very solid signal this weekend past. Wish you had been
playing in SS a lil'. Did you land the HB0? It was a new one for me and VERY
loud. Gotta love mountain reflectors ;o)
73,
Julius
Julius Fazekas
N2WN
Tennessee Contest Group
http://www.k4ro.net/tcg/index.html
http://groups.google.com/group/tcg1?hl=en
Tennessee QSO Party
http://www.tnqp.org/
Elecraft K2/100 #4455
Elecraft K3/100 #366
Elecraft K3/100 #1875
--- On Mon, 11/9/09, Mike & Coreen Smith <ve9aa@nbnet.nb.ca> wrote:
> From: Mike & Coreen Smith <ve9aa@nbnet.nb.ca>
> Subject: Topband: Electrical height of short shunt fed tower?
> To: topband@contesting.com
> Date: Monday, November 9, 2009, 4:10 PM
> Hi Gang,
>
> Some folks mentioned that the top yagi is not "seen" on my
> short tower if I
> should shunt feed it.
> Is there any proof of that? Papers? EZNEC? Anecdotal
> evidence etc? (like you
> removed the top yagi and the resonant freq on 160m remained
> the same ...)
> I'd love to hear the comments.
>
> I think I may have another stab at shunt feeding my tower
> and am curious
> more than anything as to its true electrical height.
>
> The reason for my curiosity is:
>
> A) My Tee vertical slung in the trees is now working
> "fairly" well and the
> top of it is just about the same as the tower....though the
> wire actually
> slopes up at a 45º angle, so not really vertical....also
> the top loading
> wires come towards the ground at almost 45º.
> Certainly not an ideal "vertical". . .Picture an umbrella,
> opened, sitting
> on the floor, with no material, and only 2 wires.
> That's about the shape of
> it.
>
> B) If the tower is only as tall as the first (lower) yagi
> (& the same as the
> Tree Tee) I might not bother shunt feeding it.
>
> TOWER SPECS:
> 48' Delhi, self supporting tower sunk into a massive block
> of concrete.
> Bottom yagi is for 50MHz (elements are aprox 10'
> long we'll say) with a
> 30' boom.
> Top yagi is 16' above that, identical to the first.
>
> SOme have said the electrical height is:
> 48' tower + 1/2 the boom on the low yagi (15') + half of 1
> element (5'), top
> yagi & mast invisible - so aprox 68'.
>
> Is there any chance it could be more like:
> 48'tower + 15' boom + 16' mast + 5 + 5 = 89' or am I
> dreaming? (I find it
> hard to believe there is no current in the top yagi or the
> 16' mast--?
> doesn't make sense)
>
> I keep thinking back to my Cushcraft D40 rotatable dipole,
> which has
> capacity hats nearish the element tips.....if the radio
> doesn't see anything
> past the capacity hat, why have 4 foot (or whatever they
> are) element tips
> at all?)
>
> Thanks very much,
>
> Mike
> ve9aa
>
> Mike, Coreen & Corey Smith
> 699 Rte 616 Keswick Ridge
> NB
> Canada
> E6L 1T1
> _______________________________________________
> 160 meters is a serious band, it should be treated with
> respect. - TF4M
>
_______________________________________________
160 meters is a serious band, it should be treated with respect. - TF4M
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