TopBand: Shunt-fed Towers

[Earl W Cunningham]

Dear Topbanders:

Ever since I posted info here on shunt-feed values for various-height
Rohn 25 towers, I've been playing with EZNEC trying to perfect modeling
shunt-feed systems based on the real-world parameters of my own two
shunt-fed towers.  Anyone out there who is shunt-feeding their tower on
160m and/or 80m can help me to tweak my modeling methods for greater
accuracy by providing me with the following data:

 1) Steel or aluminum tower?

 2) Height to top of tower?

 3) Width of tower?

 4) If a tapered tower, height and width of each tapered section?

 5) If top-loaded, height(s) of top-loading?

 6) If top-loaded with HF beam(s), parameters for the beam(s), i.e.,
     boom length, element lengths and element spacing?

 7) If top-loaded with wires, number of wires, their lengths, and their
    heights at both ends.

 8) Info for any other wires affecting the system, i.e., slopers or
     other wire antennas supported by the tower, uninsulated guy
     wires, etc.?

 9) If a mast extends above the tower, height to top of mast (even if
     it extends above any beams)?

10) Diameter (or wire gauge) of the shunt-feed wire?

11) Spacing (from tower) of the shunt-feed wire?

12) Height above ground shunt-feed wire attaches to tower?

13)  Value (approx ok) of capacitance required to match coax feedline?

14) Feedline impedance matched (50 or 75 ohms)?

Please respond directly to k6se@juno.com -- I'll send all respondees info
on what I come up with for their own particular system, such as 1/4-wave
resonant frequency of their tower/top-loading combo, etc.

I plan to share method(s) of modeling shunt feeds with others when I'm
satisfied the method(s) is/are reasonably accurate.

Thanks for your help, de Earl, K6SE


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