[TowerTalk] swr 75ohm

Jim Brown jim at audiosystemsgroup.com
Fri Jun 7 15:04:17 EDT 2019

SWR on a transmission line is determined by the match between the load 
(the antenna) and the line. Most SWR meters are calibrated to 50 ohms, 
so will give an incorrect reading. Among other things, this will show 
resonance at the wrong point. So to find that resonance, you want to set 
the meter to 75 ohms if you're using RG11.

On the other hand, power amps are designed to work into a 50 ohm load, 
and some (especially solid state amps) will reduce power to protect 
their transistors if the match is poor.

I feed my high dipoles for 40 and 80M with RG11 to reduce line losses, 
and use matching networks to make the power amp happy.  I use stubs for 
this, but most hams use an antenna tuner.

73, Jim K9YC

On 6/7/2019 3:09 AM, Kostas SV1DPI wrote:
> >read SWR referenced to 25, 50, or 75 ohms. VERY useful if you want to 
> find the resonance of a high dipole fed with RG11. Used it five times 
> this week to do that.
> Hello Jim
> Can you explain it better? If I use rg11 (75ohm) coax to connect the 
> dipole, do I need to switch the analyzer to 75Ohm? If I have it to 
> 50ohm what do I count?
> ...73 de Kostas SV1DPI
>   (One of SZ1A-EP6T)

More information about the TowerTalk mailing list