Topband: 160 Shunt-Fed Tower Readings

[Herbert Schoenbohm]

You may be able to improve the antennas performance by taking the out 
side insulated elements at the center  to the boom with hand wound  
chokes that pass only below 5 Mhz or lower to provide some top loading 
without impacting the Force 12 performance.  You may also be able to get 
a better feed impedance by employing a cage of three or four wires taped 
to the tower itself at or near the sweet point.  Usually if the Q is to 
high the bandwidth will suffer. Having a lower series "C" will make you 
well better as well.


Herb Schoenbohm, KV4FZ
On 12/10/2014 3:41 PM, Larry K4AB wrote:
> The antenna is a 94' Rohn 25, with a Force 12 24'boom Delta 6BA
> on top. Note that the elements are insulated from the boom. The base
> of the tower is grounded.
>
> 73 radials are attached to the base ranging in length from 130'-250'.
> 15,000 feet of radials, average length of ~200'.
>
> It is fed through a  series 1000pF 10KV Jennings vacuum variable.
> The shunt is a 4 wire cage about 3" in diameter and attached at ~45'
> level.  It is spaced about 3' from the tower.
>
> Here are the readings I get from a RigExpert AA-30 at the feedpoint:
>
> 1.830 kHz
> Series model: lZI: 59.7 Ohms
> R:59.5 Ohms
> SWR: 1.23
> X:5.6 Ohms
> C: 15893 pF
>
> What are these reading telling me,and how can I improve the antenna?
>
> Thanks, in advance!
>
> 73,
> Larry K4AB
> _________________
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