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Message-ID: <3.0.1.16.20000111112627.2d5f9c18@mail.cc.kuleuven.ac.be>
Date: Tue, 11 Jan 2000 11:26:27
To: rsgb_lf_group@blacksheep.org
From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>
Subject: Re: LF: Re: Bad experience with loop ant
In-reply-to: <387ABC73.EB1AE1BB@qsl.net>
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At 06:15 11/01/00 +0100, you wrote:
>Hello all,
>
>Walter Staubach wrote:
>
>> ....After realizing
>> my loop I found out, that the capacity of the loop itself between the turns
>> was already 800pF. That generates losses. Do you know that capacity in your
>> loop?
>
>How can one measure the capacitance of the loop itself? Any suggestions?
>
>73 Heinz, OE5EEP

By searching the 'self resonant frequency' of the loop :

1. use the loop without any external capasitors and look for the resonance
frequency (F1)
2. add a external capacitor (Cext) and look for the resonance frequency (F2)

The loop capacitance (Cint) can be calculated based on following formulas :

F1 = 1/(2*Pi*Sqrt(Cint*L)) and F2 = 1/(2*Pi*Sqrt((Cint+Cext)*L))
(where Pi = 3.1415... and Sqrt = square root)
This will lead you to 

Cint = Cext * (F2*F2/(F2*F2-F1*F1))

73, Rik  ON7YD