[BC] Long Wire

[Mike McCarthy]

We're in the midst of assembling a spider bonded detuning skirt.  The
bottom of the skirt wires are being brought in to the tower center and
bonded into a smaller loop where it will be tied to a piece of
transmission line for connection into the detuning network mounted off the
tower. At the top, each of the 6 wires are being bonded to the nearest
tower leg, but all at the same height.

This method was chosen because there are 30 transmission lines on this
tower and a girdle loop at the base and top would have proven difficult to
work around by the tenants. We believe the loops would have been cut and
then spliced back together when lines were added/removed. In this manner,
the legs of the tower which hold the banjo mounts are free and clear.

MM

> Definitions:
> -----------
> Girdle - a large wire (or cab be a hoop of tubing)
>          connecting ends of drape wires. Note:
>          girdles appear preferable at top and bottom.
>
> Spider - large wires (or tubes) radiating from a central
>          point so as to provide equal length paths to
>          the lower end each drape in the skirt or to the
>          equidistant points on the girdle between adjacent
>          drapes. Note: Modeled performance is usually better
>          when both a girdle and spider are used to balance
>          currents equally in all conductors.
>
> Attachment/
> Support: Conductive support arm of sufficient length that
>          the end away from the tower is not less than five
>          feet from any part of the tower's horizontal
>          cross-section at any point. Note: Depending on
>          tower geometry it may be necessary to provide
>          more clearance for three drapes in a six drape
>          system so that the tower is centered in a hexagonal
>          "cage."
>
> General Notes:
> ------- -----
> Drape Wire Height: The lower girdle and spider must be some
>                    distance above ground level. That may be
>                    3 or 4 feet in the case of a fenced area,
>                    or, for safety, it may be perhaps ten feet
>                    up in the air. What I discovered in the
>                    model is that an unterminated, upward
>                    extension of the drape - call it a lightning
>                    rod - above the attachment/support arm
>                    improves performance slightly. (Somewhat
>                    more at 10 or 12 feet than at 3 feet)
>
> Radiation Efficiency:  Will be ~ 95~98% of the same tower
>                        when series fed.
>
> Drive Point Impedance: Will normally be highly inductive and
>                        is strongly influenced by steel height.
>                        Resistance will be elevated as compared
>                        with the series fed case and is also
>                        influenced by steel height. Other factors
>                        are drape conductor spacing because 5 ft.
>                        is a minimum while the maximum may be a
>                        few feet greater. Modeling before
>                        construction, but the model can diverge
>                        from actual. Note in this regard that
>                        model impedance adjustment to the real
>                        world was one of the sticky points in
>                        the new DA modeling rules and resulted
>                        in incorporation of language regarding
>                        corrections to conform models to the
>                        real world. As an aside, this is what
>                        they called a pitfall for the unwary
>                        when I went to school back when we hid
>                        from the dinosaurs in caves. <G>
>