[TowerTalk] real world formula for the length of a quarter wave transmission line

[Jim Brown]

On 2/14/2013 5:33 AM, Jim Lux wrote:
> I think the OP was looking for a impedance transformer, and for that 
> application, I think small errors in length won't have a big effect. 
> Say you were using 1/4 wavelength of 75 ohm line to transform 50 ohms 
> to 112.5 ohms.. If the line were 7/32 wavelength, would it be that 
> much different? 

You're right, it would not, but the effect is not zero.  AND -- the 
resonance that a length of line like this provides can do some VERY 
interesting and useful things in broadbanding resonant antennas. That 
piece of line is a quarter wave at the design frequency, but on one side 
of the design frequency it's inductive, and on the other side it's 
capacitive.  Depending on the antenna and the rest of the system, the 
error could help or hurt.

One can learn a lot  by building a simple NEC model of a dipole, 
exporting it to SimSmith, and seeing what happens with various lengths 
of line of various impedances.

73, Jim K9YC