[TenTec] SWR Fold-Back

[Chuck (Jack) Hawley]

> -----Original Message-----
> From: tentec-bounces at mailman.qth.net
> [mailto:tentec-bounces at mailman.qth.net]On Behalf Of Larry, K4WLS
> Sent: Saturday, September 18, 2004 6:56 AM
> To: [Ten-Tec]
> Subject: [TenTec] SWR Fold-Back
SNIP
> If you put another power meter between your tuner and the ant coax,
> such as an MFJ set to "Bypass", if the power meters are calibrated
> correctly, for an SWR of 3:1 on the coax line to the ant, the forward
> power will read 150W, and the reflected power will read 50W. This
> of course neglects any losses in the "tuned" antenna tuner in the
> line. SWR = (Pfwd + P ref)/Pref
SNIP
> Regards,   Larry  K4WLS

What's happening with the definition of SWR? This isn't the first time I've
seen this. Is this what's on the Extra exam or something? SWR is the
actually the VOLTAGE standing wave ratio and  you have to take the sq root
of the power forward and reverse to calculate it using power. So SWR = (Ef +
Er)/(Ef - Er). Or, with power, it would be [sqrt(Pf) + sqrt(Pr)] /
[sqrt(Pf) - sqrt(Pr)].
Even the example given would have resulted in the number 4. The SWR for the
example of 150W and 50W would be around 3.73:1
73,
Chuck, KE9UW
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