[BC] Skirt feeds.....

[Craig Healy]

> >  I have seen the type where wires are sent up the sides to
> >  increase the effective width of the tower.   That probably
> > would work to repair any bad tower section connections as well.
>
>  Nope !
>  Remember, the antenna current is in parallel, distributed among
>  all of the parallel conductors, so a break in one will affect them all !
>
>  There are all sorts of rumors about skirts being the cure-all magic
bullet
>  when they are FAR from it !
>  Generally, you can analyze them in several ways, depending on your
>  objective.
>  If as a radiator, you need to model it the same as any other.
>  If as a feed method, then you can consider the skirt as merely the
>  last reactive component of the ATU.
>  If one is looking for the "magic" feed impedance, then the skirt is
merely
>  the last component in the ATU again, and should be analyzed as such.
>
>  It's really not much different than questioning whether a 3 leg tower, or
>  a 4 leg tower is the "better" radiator, or the better feed method.

But if the wires up the side are connected top and bottom, doesn't it
effectively shield the support tower?  Some years ago I put a wire up the
middle of a 50' tower to use as an EBS receive antenna.  The desired station
was a non-d 5kw probably two miles away.  The receiver couldn't even detect
it.  I moved the wire to the outside and it blasted in.  I would think the
external wires would take the vast majority of the current.  Almost like a
great big skin effect...

Or, how about modeling a tower structure...  Make one out of a pipe with
three wires up the sides connected top and bottom.  Then make the same thing
out of a two by four piece of wood.  How different would the resistance and
reactance be?  I would expect it to be essentially the same, if the wires
were large enough copper gauge.

Craig Healy
Providence, RI