[Amps] Measuring tank coil inductance

[Bill Turner]

ORIGINAL MESSAGE (may be snipped): 
On Tue, 23 Apr 2013 20:17:41 +0100, Chris wrote:

> When you see specs in ARRL build plans for say a
>.8 uH indctor, or see a 5 uH inductor advertised, there must be a
>definitive measuring method to arrive at the value, surely?
>
>Glad you posted, I feel I ask too many questions ;)
>
>

REPLY: 
No such thing as too many questions, within reason of course.  :-)

According to theory, pure inductance does not vary with frequency, however
the effective inductance DOES vary due to the effect of distributed
capacitance within the coil.  To get the "true" inductance of a coil it
should be measured at a very low frequency. However the effective inductance
should be measured at the frequency of operation. If a coil is used at
multiple frequencies, you will have multiple readings. Can't be helped. 

Probably the most useful way is with an accurate grid dip meter and a
precision capacitor so the combination is resonant near the operating
frequency. Done carefully, you should get within about 1% of the effective
measurement. Any closer than that will probably be thrown off by unavoidable
stray capacitance. 

Bill, W6WRT