# [TowerTalk] Transmission Line theory

Rick Karlquist richard at karlquist.com
Tue Jul 1 15:34:20 EDT 2008

```Your best bet is to determine the characteristic impedance
for the corresponding microstrip line, and double it.
The height above ground plane will be half of the conductor
to conductor spacing of the open wire line.

Here is a calculator for microstrip:

http://chemandy.com/calculators/microstrip_transmission_line_calculator.htm

If you have a line with 20:1 ratio of conductor spacing to
conductor diameter (round wires) compared to the same
line with square wires, where the square wires have the same
cross sectional area as the round wires, the square conductor line
has 3.5% more impedance, 410 vs 395 ohms.  At least according
to this calculator.

Rick N6RK

Paul Baldock wrote:
> Does anybody know the formula for calculating the characteristic
> impedance of a transmission line consisting of 2 parallel square
> conductors (in air)?
>
> Thanks
>
> - Paul KW7Y
>
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```