[Elecraft] Measuring Inductance with the MFJ-259

[W3FPR - Don Wilhelm]

Darrell,

Caution,  The toroids should be wound as instructed - you may measure them,
but please do not try to make the inductance equal that indicated in the
manual/schematic because those inductance values are either what was
measured on someone else's inductance meter, or they are approximate values.
If you want to calculate exactly the inductance required, you must calculate
the entire low pass filter design, and then be certain to measure the
inductors at the frequency of use - and with a properly calibrated
inductance meter - I would bet the MFJ259 could be off by as much as 20%
until proven otherwise by measurement of standard inductors at various
frequencies.

No Q-Dope or fixatives of any kind should be used for Elecraft kits unless
specifically stated - I have never experienced any problems with toroids and
have never used anything to hold them in place.  One of the K2s I built is
being used successfully as a mobile - in an 18 wheeler - check the QRZ.com
listing for W4GNS if you have any doubts.

73,
Don W3FPR

> -----Original Message-----
>
> As I build my second K2, I want to try to measure the inductance of the
> toroids with my MFJ-259. The MFJ manual has instructions on how
> to do this.
> Essentially one builds a series LC circuit and measures the resonant
> frequency and then calculates the inductance.
>
> Has anyone tried this and have any tips or tricks to pass on?
>
> Am I correct in assuming I can adjust the value of inductance on a toroid
> slightly by compressing or expanding the spacing between turns?
> If so what
> can I use to hold the turns in place. Friction is probably good
> enough, but I
> wonder about a few drops of something like Q-Dope. Comments?
>
> 73,
> Darrell
>
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