Arsk0jn wrote:
> You can measure the reactance of a resistor if you have two that are very
> close to the same resistance value with either a grid-dip meter or MFJ-259...
I didn't go through Joe's solution, but out of curiosity I decided to try
to measure the inductance of some Xicon 51-ohm, 5W metal oxide resistors
that I got from Mouser. The one I grabbed out of the box measured 50.3
ohms.
To test, I added silver-mica capacitors of several values in series (keep-
ing leads as short as possible), and used my MFJ259 to measure the resonant
frequency with each. Knowing that frequency, I calculated the reactance of
the capacitor, and using that reactance calculated the inductance of the
resistor.
Here's what I got, and I don't mean to imply by the number of significant
digits that I can measure that accurately. You'll need to use a fixed-
width font to see what I'm seeing:
CAPACITOR FREQUENCY REACTANCE INDUCTANCE
--------- --------- --------- ----------
148.0 pf 57 MHz 18.9 ohms 52.8 nH
50.2 pf 100 MHz 31.7 ohms 50.5 nH
26.8 pf 135 MHz 44.0 ohms 51.9 nH
Average= 51.7 nH
So... for THIS VALUE of these particular resistors, this looks like a
pretty good estimate of inductance. With the resistor alone, the SWR
indicated by the MFJ259 was only a couple of needles width from minimum,
but indicated 2:1 by 104 MHz. Incidentally, the indicated resistance at
135 MHz was slightly higher than 50 ohms in the above experiment, just
a little less than 60 ohms.
I didn't have time to measure other values, but I hope this is useful.
73,
(the other) Jon
--
Jon A. Barclay N5JA (ex-AA5BL)
N5JA@contesting.com
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