FWIW, the MFJ-269 uses 12bit A/D's and displays impedance
up to 1500 ohms. I haven't sat down a real careful comparison
(e.g. calculating percentage error), but the MFJ-269 seems to
produce readings that are consistent with cross-checks I have
made on an HP network analyzer.
73 de Mike, W4EF...............................
----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: "Tower Talk List" <towertalk@contesting.com>
Sent: Friday, December 10, 2004 6:11 AM
Subject: Re: [TowerTalk] accuracy of antenna analyzers
> 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
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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