When measuring inductance or capacitance with the MFJ-259b readings vary,
depending on the frequency. I usually run a part through a 10mhz sweep. There
will be an area in the "middle" where the calculated value changes much slower
than at the extremes, and the measured values will correlate nicely with the
AADE LC meter. This happens between 6 to 9 mhz; I've "standardized" on 7mhz
for measurement. Correlation to parts previously measured on the AADE meter is
within 2 or 3 percent, and often closer.
The measuring of L and C values for the 259b is stated as a reactance range,
that being between 7 and 650 ohms. So, working backwards from 7mhz, its
measurement range is
Inductors = 0.15uh to 15uh and Capacitors = 35pf to 3200pf
I've taken some license in those end points to make it easier to remember, but
they're close, reactance wise. Also, its easy to see we shouldn't be throwing
away our AADE, BK, or HP LC meters because the MFJ range is very restricted.
The mfj has a 259 connector output, so you need an adapter to measure parts
values. I've found the type used can be critical to the ability to repeat
value determination. Leads longer than 1 to 2 inches need not apply, and that
includes coax with alligator clips on the end. The best I've found is to to
use a banana plug, without its insulator, in the 259 center connector with a
nut screwed over the post, and another nut screwed over the nearby ground
connector. Parts connected directly between them.
I'm going to copy this post over to the 259b's yahoo forum.
73 - Jim - K9JFK
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Message: 9
Date: Wed, 31 Mar 2010 10:23:51 -0500
From: "Jeff Blaine AC0C" <keepwalking188@yahoo.com>
Subject: Re: [Amps] LCR meter.
Jim,
My question is to the fundamental accuracy of the MFJ vs. the effects on
calibration variation. Is the MFJ really this inaccurate, or is the
accuracy in your case atypical. It would be interesting if someone else
could do a controlled test with the MFJ vs. a lab type unit (well, a unit of
known capability).
I only have the AADE meter here in are the Fo there is variable; as well as
the MFJ.
73/jeff/ac0c
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