Topband: Top Loaded Vertical

[Herb Schoenbohm]

Charlie K4UWH Wrote:
> I have an aluminum vertical element that is 67' tall.  I want to top-load it
> on 160 meters and would like to use a three wire approach for physical
> symmetry in support of the vertical element.  
> 160?  I was guessing about 40' but that was a wild guess.  
>
> _______________________________________________
>
>   


Charlie remember any top loading connected  that far (20') below the top 
reduces the over all vertical element height above that point and you 
will then end up with a 40' top loaded vertical rather than a 67' foot 
top loaded vertical.  I would recommend guying with two sets of guying 
with insulated material such as Philystran at 40 feet.  Put the top 
loading set from the top sloping down at an angle (with respect to the 
pole) of no less than 45 degrees and no more than 25' where insulators 
are placed. (Top loading sloping wires have a point of cancellation if 
they are to long or the angle is acute.)

Break up any remaining wires to ground at least every 40-50 feet. You 
can get about 10% more top loading by connecting  the top three wire 
spiders together end to end (inside the insulators) to form a skeleton 
cone.  This should increase the amount of top loading and bring you 
closer to 1/4  wave. These are approximations but if you know someone  
who can model this you can have more assurances that what you are 
putting up will give you the maximum efficiency at the radiation angle 
lobe you are looking for.


 If the pole is insulated and you have a directed feed the 20 to 30 ohms 
resulting impedance, maybe even a bit lower if you have a near perfect 
ground, can be matched with an Un-Un or simple L network.  If the pole 
is grounded you can shunt feed it with a tap about 30 to 40 feet but you 
will need to tune out the inductive reactance of the shunt with an ATU. 

Remember that resonance is not crucial.  What is more important is 
matching what you end up with and the ground system this Marconi will 
need to make it efficient.

Good Luck with your project.

Herb Schoenbohm, KV4FZ.