Topband: Top Loaded Vertical

[Richard (Rick) Karlquist]

There is a point of diminishing returns on the sloping
top loading wires.  The radiation resistance increases
with increasing length up to a point and then
decreases with further lengthening.
IMHO, you want just enough wire to maximize radiation
resistance.  If that doesn't achieve resonance,
then put a loading coil at the bottom.  Losses will
tend to be dominated by ground resistance rather
than coil losses, since it is relatively easier
to reduce the latter.

All of this is easily modeled on EZNEC, or other
programs.  I highly recommend modeling for this
type of problem.

Rick N6RK


k8gg at voyager.net wrote:
> 
> Charlie, K4UWH wrote:
> 
>> I have an aluminum vertical element
> that is 67' tall. I want to top-load 
>> it 
>> on 160

> 
> Attaching 3 wires each
> 40 foot long at the top of your 67 foot vertical could bring the resonant
> frequency close to 1830 KHz.  The actual frequency
> will depend on the angle at which the top loading wires slope
> down from the top of the vertical.    It will
> also depend on the diameter of the wires used, and the sizes of the tube
> sections used to construct the 67 foot vertical.  The feed point
> impedance could be as low as 18 ohms with a good ground radial
> system.