[TowerTalk] RG-149: 50 ohm/70 ohm - does it matter?

[Richard (Rick) Karlquist]

On 12/13/2013 4:49 AM, kr2q at optimum.net wrote:
>
>
> So what's the diff if it's 50/52/70/75 ohm feedline?  The mismatch (if not 50) will be "nothing" and therefore the extra loss will be "nothing."  Transmission line is always transmission line.  As long as the line itself is not "lossy," does it matter?
>
> Looking for sage advice for those with degrees or prowess in this area.
>
> de Doug KR2Q

Suppose his "50 ohm" antenna has a 1.5:1 SWR and its impedance is 
actually 33.3 ohms.  Suppose he operates on a frequency where his
75 ohm feedline is an odd multiple of a quarter wavelength.  Then
the impedance his transmitter will have to drive will be 169 ohms,
an SWR of 3.4:1.  This will require a transmatch.

It really does matter whether the line is 50 or 75 ohms.

Rick N6RK