> Herbert Schoenbohm wrote:
> >
> So give some consideration to either a
> > square or delta (triangular) top hat supported by corner supports that
> > drop
> > the vertical wire. Two cross wires (on the square wire top hat) with
the
> > vertical drop in the center or three intersecting wires for the triangle
> > top
> > hat should save space, improve efficiency, and allow for a lower
vertical
> > overall height. > >
> > Herb Schoenbohm, KV4FZ
>
> I have a 90 ft vertical with four 30 ft top wires that follow the
> guy ropes down at a 45 degree angle, and it resonates around 1.8 MHz.
> I have modelled various top hat configurations and the limitation on
> top wires that slope down (umbrella configuration) is that the tips
> need to be at least 2/3 the height of the vertical section. If you
> try to make them go lower than that the radiation resistance starts
> to drop. Using more than 4 or putting a skirt on them is somewhat
> helpful, but it gets to be a mechanical nightmare especially if you
> have various other guy ropes in the area.
>
> Rick N6RK
Rick, There is significant cancelation, I have found, with the sloped top
hat 3 or 4 wire sloping guy configuration of over 20 per cent additional
length to that of the vertical. One reaches a point of diminishing returns
indeed.
However, what I was trying to describe was a (non sloping) flat top square
or triangle with cross connecting wires thus forming a skelton top hat. The
vertical wire drops from the precise center. The benifits in small area lots
would be worth the consideration of an extra support in the case of the
triangle top load or two extra supports in the case of the rectangle or
square top hat. In some parts of the country with plenty of trees (I just
got back from two weeks in Minnesota) nylon rope supports may be all that is
required to get a good topband TX antenna.
Herb Schoenbohm, KV4FZ
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|