Kind of hard to do that on a hand wound 1/4" copper coil for a tank
circuit...
Would work for commercially made stuff though.
Cecil
K5DL
----- Original Message -----
From: "RICHARD SOLOMON" <w1ksz@q.com>
To: "Amplifier Reflector" <amps@contesting.com>
Sent: Wednesday, March 31, 2010 5:39 PM
Subject: Re: [Amps] LCR meter & measuring components
>
> Wouldn't it be easier to look up the Part Number in the Catalog ??
>
> 73, Dick, W1KSZ
>
>> From: pfizenmayer2@q.com
>> To: larry@w7iuv.com; amps@contesting.com
>> Date: Wed, 31 Mar 2010 15:30:39 -0700
>> Subject: Re: [Amps] LCR meter & measuring components
>>
>> FWIW - There is a pretty definitive method of measuring an inductor which
>> will
>> yield its low freq inductance , its self resonant frequency , and the
>> distributed capacitance.
>>
>> It is normally done with a Q meter but can be done with any instrument
>> with
>> variable freq below the self resoannt freq that will show what
>> capacitance
>> is required to resonate that inductor at that frequency.
>>
>> Just measure capacitance to resonate at several freqs well below the self
>> resonant freq - theoretically two freqs will do but I prefer three or
>> four
>> as a check that nothing screwy is going on .
>>
>> Then plot C to resonate on the vertical scale and plot 1/f squared on the
>> horizontal axis. The points will (or should) fall in a straight line. If
>> not , an average thru the points will get you very close. The line will
>> intersect the vertical axis and that point is the distributed
>> capacitance.
>> The intersection with the horizontal axis is the self resonant frequency
>> (zero external capacitance to resonate)
>>
>> The slope of the line is the low frequency or "true" inductance.
>>
>> Dunno if I can do this equation but here goes.
>>
>> Basically you take a region of the sloped line and read off a change in
>> 1/(f
>> squared) for a change in capacitance to resonate (Delta 1/F^2) and
>> (Delta
>> C)
>>
>> Then L is 1 /(4 pi squared X Delta C / Delta 1/F^2).
>>
>> Or , if you want to know the "apparent" inductance at any frequency then
>> read off C to resonate at that frequency , and using the Co or
>> distributed
>> capacitance at the intercept the L apparent is L(1+ Co/C)
>>
>>
>> If you just want the self capacitance - two frequencies , one twice the
>> other - F1 (C1 to resonate ) and 2F1(C2 to resonate) can be used to
>> calculate
>> self capacitance = (C1-4C2)/3 .
>>
>> If I still had my web site I could put this on it but Qwest in their
>> infinite customer service wisdom dropped us .
>>
>> Ancient ancient history when we did not have all the fancy instruments of
>> today .
>>
>> Hank K7HP
>>
>>
>>
>>
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>
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