VSWR Calculation

[evfd1625]

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Can someone refresh my memory on calculating VSWR from forward and reflected power? Just helped someone with some transmitter problems and had 15w reflected, 30w forward out of a 50w transmitter. Fixed the antenna and got 48ish Watts forward and 1 reflected.

 

[cabletech]

What type of radio & frrequency? What type of meter? Normally, you can connect the radio get your readings, reverse the connections and see if you get the same readings.

If yu do then your meter is reading fairly correct.

 

[evfd1625]

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It was a Kenwood, 2 meter, and a Bird watt meter.

 

[nd5y]

30 W forward, 15 W reflected is 5.83:1 VSWR
48 W forward 1 W reflected is 1.34:1 VSWR

Bird has a neat RF calculator spreadsheet but it appears that their web site isn't working.
http://www.bird-electronic.com/en/Resources/TechnicalTools.aspx

The formula to calculate VSWR from forward and reflected power can be found at http://en.wikipedia.org/wiki/Standing_wave_ratio

 

[majoco]

SWR = (1 + (√reflected power/forward power)) / (1 - (√reflected power/forward power))


according to my ARRL handbook 1982.

The ITT Ref Data book gives the Wiki formula - far too complicated for this guy!