hi all,
i added to my web pages a schematic and pc board pattern for a circuit that
i'm using to measure inductances in the mH range. in building the R2
receiver, i needed to match inductors to within 1%, and i didn't have an L
meter. i found an LC oscilator circuit that goes down to audio freqs, and
modified it just a bit.
it is a pretty simple circuit, using 3 NPN transistors, a voltage
regulator, and a couple of other discrete passive components. i built it
on a pc board but it should be able to be done just fine with just about
any construction method you can think of. the trick is that it needs an
external frequency counter that can measure in the AF range. if you want
precision, the counter should be able to go down to the 0.1 Hz resolution.
build it so the L's connect by micro test-clip leads (radio shack).
oh yeah, be sure to avoid the mistake i made: if you want better accuracy,
measure the values of the 1 uF caps before soldering them in.
simple instructions for use are on the web-pages. the circuit has worked
like a charm for me, reproducibility on multiple readings of the same
inductors is about 0.1 mH in 100 mH (0.1%), though I don't know the
absolute accuracy yet.
http://genome33.ped-gen.uiowa.edu/hamradio/LC_OscillatorSchematic.html
let me know if you can think of any improvements for it, i'd like to know.
73,
--adam
=================================================================
Adam B. Kanis, N2BRT QTH: Wellman, IA (Near Iowa City) EN41ck
adam-kanis@uiowa.edu QRP ARCI : NorCal : QRP-L: G-QRP : CQC
Straight Key : OHR-100 40m : Carolina Beam oriented N/S
** On the Web at http://genome33.ped-gen.uiowa.edu/hamradio **
=================================================================
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