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[TowerTalk] accuracy of antenna analyzers

To: "Towertalk" <>
Subject: [TowerTalk] accuracy of antenna analyzers
From: "Jim Lux" <>
Date: Thu, 9 Dec 2004 20:40:25 -0800
List-post: <>
Does anyone know of any description or analysis of the accuracy of the
various antenna analyzers.  The MFJ analyzers use 3 A/Ds to measure detected
voltages to 8 bits, and then they compute R and X from the three
measurements.  Aside from calibration errors, what's the uncertainty in R
and X given that the voltages are only digitized to 0.5% accuracy, etc.  Is
an X measurement good to 1 ohm, 5 ohms, etc.?  Is there some nice (or not so
nice) equation that would give the measurement uncertainty for R and X,
given a particular R and X measurement (that is, I expect that if R is close
to 50, the accuracy is better, but if R is 500 ohms, it's somewhat

I've got the ARRL articles on measuring the VSWR measuring performance with
calibrated mismatches, but I'm really interested in how accurately these
devices measure the reactive component.

Jim, W6RMK


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