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# some problem about VSWR (HELP!)

## some problem about VSWR (HELP!)

(OP)
Hello,

I just do not understand an expression about VSWR. It is about something is defined as 1:2.5 VSWR.....I dont know what do it mean. Is that means VSWR=2.5 ???  or other meaning?

Pls help!

Raymond

### RE: some problem about VSWR (HELP!)

vswr=voltage standing wave ratio

vswr = 20 log (Vpk/Vo) where Vo is the voltage at matched conditions.

you get mis-match when there are impedence discontinuities on the line.

a matched source-load has a vswr of unity.

### RE: some problem about VSWR (HELP!)

VSWR 1:2.5  means  VSWR = 2.5 which is the correct expression.

VSWR < 2.0 is OK, best VSWR is 1.

Regards

### RE: some problem about VSWR (HELP!)

(OP)
Thank you very much!

### RE: some problem about VSWR (HELP!)

VSWR tells how much power will be reflected back to the source. The reflection coefficient will tell you what percentage of the incident signal is being reflected. In terms of scattering parameters, the reflection coefficient is also known as S11. If you want to determine how much power is being reflected back, use your VSWR measurement and the formula R = (VSWR - 1)/(VSWR+1) where R is the reflection coefficient (the incident signal percentage being reflected back).

### RE: some problem about VSWR (HELP!)

The most basic definition of Voltage Standing Wave Ratio (VSWR) is the ratio

(maximum RMS voltage)/(minimum RMS voltage)

where the maximum and minimum voltages occur at different points along a particular transmission line. It should be obvious from this definition that the ratio can never be less than 1.

The expression 1 : 2.5 as a VSWR is incorrect and might have been intended to be 2.5: 1.

2.5:1 as a VSWR is ordinarily simplified to 2.5

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