On Thu, 9 Dec 2004 20:40:25 -0800, Jim Lux wrote:
>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.
I have spent a fair number of hours with a CIA-HF, borrowed from another ham,
and own an MFJ-259B that I've calibrated per Tom Rauch's applications note.
Tom says that the concepts of the two analyzers is similar. None of the
analyzers
of this class give you the sign of the reactance. Somewhere on the web I
googled
to find an excellent review by a ham who compared three or four of them to an
accepted standard, a GR 1606 bridge. It might have been on one of the
contesting.com reflectors. It is worth chasing down.
Some general impressions. These are 10-20% analyzers. They essentially
measure the magnitude and the phase angle, then compute the R and X
components. The closer they are to 50 ohms (or 1:1 VSWR) , the better the
accuracy. The CIA-HF will give you an reading up to 1K ohms. The MFJ quits
around 400 or 500 ohms. I wouldn't put a lot of credence in the answer of
either in
that range. BUT -- I have measured a lot of ferrites using a CIA-HF in a
disciplined manner to create graphs of their characteristics, and I get curves
that
are consistent and believable in the context of mfr data. The CIA-HF will not
display the smaller component, R or X, within 5 degrees of 0 or 90 degrees. I
view that as acknowledging the modest accuracy of the measurement. MFJ may
be doing the same thing when they quite at 400-500 ohms.
Jim Brown K9YC
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