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

[Steve Hunt]

That's right - and it doesn't have to be that close to a 1/4 wl or odd 
multiple to be a problem.

If you feed a 50 Ohm load through a 75 Ohm line, any line length from 
around 0.15wl thru 0.35wl (or repeats) will give you an SWR(50) of 2:1 
or greater. That's enough for the protection circuitry in many radios to 
beginning backing off the output power.

Steve G3TXQ



On 16/12/2013 00:21, Richard (Rick) Karlquist wrote:
>
>
> If you are driving a multiband antenna, it is actually
> quite likely to have near a 1/4 wl on some frequency especially
> if you have a few hundred feet of coax.
>