[TowerTalk] MODEL FOR TOWER

[Steve Maki]

On 04/24/19 8:40 AM, jimlux wrote:

>> I have always just guess when converting a tower to a wire diameter. 
>> The original poster seemed concerned that his tower would effect his 
>> horizontally polarized HF beams, I have not seen that occur.

> I think the question would be about the SSV/BX style tower which is 
> larger at the bottom than the top. Rohn 25 or 45 are "small" compared to 
> a wavelength in the horizontal direction, so they can be modeled as a 
> "fat wire" - just like a cage dipole element, for instance.
> 
> The tower in question is 7.5 ft at the bottom and 2 ft at the top 80 ft 
> high.
> The OP was asking about a 20m Yagi to be mounted at 60 ft, where you'd 
> effectively have big square loops that are about 3 1/2 ft on a side (14 
> ft total perimeter)  near the antenna, as well as diagonal struts of 
> some length.
> 
> The wavelength is 60-70 ft, so those squares are about 1/4 wavelength in 
> perimeter.  If they were 1/10th wavelength, I'd say "model it as a big 
> wire", but that's big enough that there might be some interaction, 
> especially since they will be effectively "inside" the Yagi.

In the scenario where you have a large enough tower that a nearby 
horizontal antenna is impacted by the tower's horizontal members - is 
there a fundamental difference between a lattice tower compared to a 
cylinder of like diameter?

I've assumed no, but now you have me wondering.

-Steve K8LX