Topband: measuring transformer core inductance

[Bob Tellefsen]

Steve
To measure inductance at the frequency of use, I use either of two
instruments.
I have the Autek VA-1 and the AEA HF-CIA antenna analyzers.  This method
would
work with the MFJ anatenna analyzers also.
To measure inductance with some accuracy, I connect an inductor and
capacitor
in series with a 51 ohm resistor across the input terminal of the analyzer.
Then I tune through the expected frequency, looking for the lowest SWR
indication.
At resonance, the L and C "disappear" and the meter is looking at just the
51 ohm
resistor.  Knowing the value of C, you can readily calculate the value of L.

I too have the type of LC meter you describe, and yes, it's only useful for
measuring inductances for audio frequency work.  However, since I tinker
with
LC audio filters, it still gets used.
73, Bob N6WG

-----Original Message-----
From: topband-bounces at contesting.com
[mailto:topband-bounces at contesting.com]On Behalf Of Steve Flood
Sent: Thursday, November 13, 2003 5:37 PM
To: topband at contesting.com
Subject: Topband: measuring transformer core inductance


I picked up an LCR meter for the main purpose of winding transformers and
being able to nail down the actual inductance and transformation ratios.
The meter was advertised as "Frequency to 15MHz" but as it turns out it
meant that it measures frequency rather than generates frequency.  It
actually generates a 1 kHz signal for measuring inductance which probably
makes it worthless for measuring inductance at 1.8 MHz.  Is this the case?
I read where core permeabilities change with freuquency.  My question to the
group is what do you use to measure the inductance of the windings so you
know when you reach the desired ratios?  I've had miserable luck doing it by
formula and thought the meter would cinch it for me.

I cannot seem to locate website charts that show inductance/frequency curves
for the cores on Amidon or Fair-Rite websites.  This would help to estimate
where one needs to go when they wind up a core.

Any help here?

Thanks, Steve KK7UV
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