One thing I have been working on to top load an antenna (in this instance a
MW Broadcast band antenna) is to guy the top of the tower. Connect wire
guys to the top and then insulate at some point (yet to be determined, but
for this MW Band example 30' on a 150' tower). At the insulated point, run
a wire from guy (or I should say top hat wire) to another wire. Creating a
nearly complete top hat the will appear to be like an umbrella.
I have seen this done at a few very low frequency MW stations and a few LF
as well.
I am working on modeling it in EZ NEC (in my spare time HA!) but so far it
seems to be working out pretty well.
Kent, K9EZ
Raleigh, NC
On 3/20/07, K4RO Kirk Pickering <k4ro@k4ro.net> wrote:
>
> I just converted a 40 meter aluminum vertical (33') to an 80 meter
> vertical. I attached about 33 feet of #12 wire to the top of the
> aluminum whip, and then hoisted the wire over the top of a nearby
> 60' tree. I had to trim it a few times to get it right where I
> wanted it. With a good choke balun on the feedline, and (currently)
> about 32 radials, the antenna is now starting to play. I'm getting
> more QSOs out of this piece of aluminum on 80 meters than I ever
> got out of it on 40 meters.
>
> 73
>
> -Kirk K4RO
>
>
> On Sat, Mar 17, 2007 at 10:18:28AM -0700, Lee Buller wrote:
> >
> > Ladies and Gents,,,
> >
> > Last year, I build a homebrew 1/4 wave verticle and mounted it on the
> ground with 16 radials underneath it. I am in the process of adding 16 more
> radials. The antenna is made out of aluminum tubing starting with and 1"
> 1/4 and going down to 3/4". The length is 32 feet and with 16 radials under
> it...it resonates at 7.100...at least it is flat there...and the MFJ 259
> says it has imdedance of 55 ohms...R=53-55, X=3-6, Theta is 10
> degress, Works good too.
> >
> > What I want to figure out is how to had a "top-hat" to the antenna to
> bring it down to 80 meters. I know that the MFJ brand of verticals uses a
> top hat loading scheme and I wonder how you calculate or figure out the
> capacitance one would need to build something like this? Or, is it trial
> and error?
> >
> > In addition, the top of the antenna is fairly small tubing (I am
> afraid I will bend it with to much weight or load) and I need to come down
> on the antenna about 8 feet to install the top hat. I guess one would have
> to use trial and error to find the right combination of "spokes and Lenghts"
> to make the capacitance hat. Looking at the Handbook, it does not really
> have a "formula" for such things.
> >
> > Anyone have any insite? Give me a starting point?
> >
> > 73
> > Lee - K0WA
> >
> >
> >
> > In our day and age it seems that Common Sense is in short supply. If
> you don't have any Common Sense - get some Common Sense and use it. If you
> can't find any Common Sense, ask for help from somebody who has some Common
> Sense. Is Common Sense devine?
> > _______________________________________________
> >
> >
> >
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