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#11
July 9th 15, 11:10 PM
posted to rec.radio.amateur.antenna
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An antenna question--43 ft vertical
Wayne wrote:
wrote in message ... Wayne wrote: wrote in message ... John S wrote: On 7/8/2015 7:27 PM, Wayne wrote: "John S" wrote in message ... On 7/7/2015 1:44 PM, wrote: Ian Jackson wrote: In message , Jerry Stuckle writes Sure, there is ALWAYS VSWR. It may be 1:1, but it's always there. If there's no reflection, there can be no standing wave. So, being pedantic, there's no such thing as an SWR of 1:1! Despite the name, VSWR is defined in terms of complex impedances and wavelengths, not "waves" of any kind. Actually, VSWR is defined as the ratio of Vmax/Vmin. That's also my understanding of the definition. In fact since SWR is defined as the maximum to minimum voltage ratio, the "V" in VSWR is redundant. Sort of. There is also ISWR but it is not used frequently. # Not sort of, but is. # There is also PSWR. And both go back to the Vmax/Vmin definition. The PSWR is a tricky one because you can end up with a power ratio instead of a voltage ratio. # Actually, no, PSWR has nothing to do with power ratios as in RF power, # rather it has to do with power ratios as in values raised to the second # power. What I'm getting at is that the ratio of forward to reflected power needs a bit more math to get to VSWR. Yes, in terms of power: VSWR = (1 + sqrt(Pr/Pf))/(1 - (sqrt(Pr/Pf)) Where Pf = forward power, Pr = reflected power. -- Jim Pennino |
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