VSWR question

[Leiser]

Hi all,

I have a question about VSWR. Sometimes VSWR is specified as a ratio, for example. 2.0:1 what does exactly mean this ratio? and would that mean if it was 1:2.0

Thanks!

 

[VEBill]

It's normally written as 2.0:1 (not the reverse).

Here's a good and fairly-complete introduction:

http://www.arrl.org/tis/info/pdf/q1106037.pdf

 

[fringe]

Here are two websites you might look at:

http://www.microwaves101.com/encyclopedia/vswr.cfm

http://www.antennex.com/preview/vswr.htm

 

[Higgler]

V = voltage
S = Standing
W = Wave
R = Ratio

You could say it's 1:2 also, that's a ratio, just depends on what your reference is. Everyone uses a number greater than one though.

Picture a wave on the ocean breaking off the shore wall moving back out to sea and meeting another wave coming in. When they meet, they add up and become larger. Their standing wave ratio is the original height of say one foot, compared to the height where they sum up of say 2 feet. That would be a 2:1 standing wave ratio measured in distance.

VSWR is similar except it's the voltage on a transmission line, and the ratio is the peak versus the minumum.

Large standing waves mean alot bounced back and the voltage is actually twice as high as it could have been for a peak and virtually zero volts for a minimum which makes a large ratio or large VSWR.

More voltage can cause arcing breakdown, blow up your electronics, it means your electronics receiving your energy isn't efficient since energy bounced back. Large VSWR is bad stuff generally.

kch