[TowerTalk] Detuning a tower .... was Open-wire transmission line

[Joe Subich, W4TV]

On 1/2/2024 12:49 PM, David Gilbert wrote:

> I've often wondered why running a wire down the center of a tower
> wouldn't create the same coaxial section as surrounding the tower
> with multiple wires.
Never tried it or heard of anyone who has used the "internal wire"
method for detuning a tower.  Since the goal is to reresonate the
tower to another frequency - either the entire structure or by
electrically breaking up the structure into non-resonant pieces -
at which it carries minimum current on the "interfering" frequency,
I don't know why the internal wire approach would not work at least
for the "full structure" case.

73,

    ... Joe, W4TV

On 1/2/2024 12:49 PM, David Gilbert wrote:
> 
> 
> Hi, Joe.
> 
> Detuning a tower and shunt feeding a tower seem to be essentially the 
> same mechanism except for whether there is a feed or not, and I've often 
> wondered why running a wire down the center of a tower wouldn't create 
> the same coaxial section as surrounding the tower with multiple wires. 
> Has anyone successfully tried this?  I couldn't find much of anything by 
> searching online.
> 
> Take care es 73,
> Dave  AB7E
> 
> 
> 
> On 1/2/2024 7:17 AM, Joe Subich, W4TV wrote:
>>
>>
>> A tuned skirt is a detuning kit.  In essence, the skirt is a coaxial
>> section while a single wire is an open wire line.  They work the
>> same way short one end, tune the open end with the appropriate
>> reactance (capacitor).  If one knows the Zo of the line section,
>> determining the starting capacitance is straightforward.
>>
>> I would prefer a three or six wire skirt for detuning simply because
>> it is easier to calculate the effective diameter(s) of the triangular
>> tower section and the skirt.  Any errors should be systematic and
>> the *ratio* of the two diameters will be consistent.  However, either
>> the single wire (loop) or skirt will work to detune a tower.
>>
>> 73,
>>
>>    ... Joe, W4TV