[TowerTalk] Transmission Line Formula

[David Gilbert]

Thanks!  I should be able to work with that.  I'm trying to model a 
transmission line equivalent for decoupling stubs on a yagi element 
(wire suspended below tubing), and the characteristic impedance of the 
theoretical transmission line in the model needs to be the same as the 
physical stub on the antenna since it makes a difference on the effect 
at frequencies other than the one "being decoupled".  EZNEC reputedly 
doesn't model closely spaced wires all that well so I didn't want to 
rely only on modeling the stub, and I thought the comparison might be 
interesting as well.

I appreciate the help.  Take care es 73,
Dave   AB7E


Richard (Rick) Karlquist wrote:
> It is in Reference Data for Radio Engineers, Chapter 24, configuration N.
>
> Zo = [60/(epsilon^.5)]* ACOSH {[4D^2/d1d2 - d1/d2 -d2/d1]/2}
>
> where epsilon is relative dielectric constant
> D is center to center spacing
> d1 and d2 are the wire diameters
> ACOSH is inverse hyperbolic cosine
>
> Of course I wonder why would anyone deliberately use different diameters?
>
> Rick N6RK
>
> David Gilbert wrote:
>   
>> The formula for calculating the characteristic impedance of a parallel 
>> wire transmission line is readily available for the case where the 
>> conductor diameters are equal, but can anyone point me to a formula or 
>> online calculator for the case where the conductor diameters are not 
>> equal?  I could have sworn that the ARRL Antenna Book once had it, but 
>> so far I have been unable to find it either there or anywhere online.
>>
>> Thanks in advance,
>> Dave   AB7E
>>
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