[TowerTalk] Transmission Line Formula

[David Gilbert]

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