To add to my earlier post the cage in my case is only supported by guy wires
insulated from the tower. The wire skirt tap point in my case is at 41 feet
with an A3 at the top of the Rohn 45 tower. I have a 15 foot stinger on top
of that but I am not to sure it is not erased by the top loading of the beam.
There is a fascinating paper at the 1996 NAB convention on skirt wire cage
feeds vs series feeds for AM towers presented by Ron Rackley, P.E. (along with
Bobby Cox, PHDEE of Kintronics, which IMO seeks to dispel some of the myths on
skirt fed towers previously held to by other consulting engineers. They
reveal in their tests that the increased bandwidth resulting from the cage
feed is a matter of increased circumference. They used NEC 4.1 and then went
to field tests which showed that similar improvement in B/W can also be
obtained with a series fed bottom insulated tower having the same cage
connected to the top and bottom to the tower.
The paper can be downloaded at http://www.dlr.com/dlrweb/Resumes/lrobert.htm
and when you read it there are some surprises.
Herb Schoenbohm, KV4FZ
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