[NLRS] Calculating 1/4 Wavelength coaxial stub?

[hill195 at mchsi.com]

I have always used 246/f*Vf. I use 234/f for computing 1/4 wave radials for a
vertical antenna. No Vf applied. The smaller number is the result of distributed
capacitance applied to the radial conductor as a result of "End Effect" making
it slightly shorter. That, having been said, I never relied upon the formula
entirely though, due to nuances in Vf from one manufacturer to the next or batch
of coax to the next. I Always cut slightly longer, then trim and sweep with an
SWR analyzer or equivalent piece of test equipment and make my final trims. This
is especially important in coaxial power splitters on an array. Those last few
millimeters can have a profound effect on radiation pattern. I'll craw back
under my rock now :)

73, John, K0PW


----------------------  Original Message:  ---------------------
From:    Scott <acepilot at bloomer.net>
To:      NLRS List <nlrs at mailman.qth.net>
Subject: [NLRS] Calculating 1/4 Wavelength coaxial stub?
Date:    Tue, 7 Oct 2008 10:37:00 +0000

> 
> 
> To make a shorted 1/4 wavelength stub, I would have thought that the 
> formula would be (234/f)*Vf where f is the frequency and Vf is the 
> velocity factor of the coax.  Searching google briefly, I saw a site 
> that had the formula as (246/f)*Vf.  Of course at 1152 MHz, that's 
> "only" a difference of about 2mm.  Which formula will get me closer?  
> Or...is there a different one alltogether?
> 
> -- 
> Scott N0EDV
> http://corbenflyer.tripod.com/
> Flying Corben Junior Ace - Building RV-4
> Gotta Fly or Gonna Die
> 
> 
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