Dip Meter TC Tuner

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "S & J Young by way of Terry Fritz <teslalist-at-qwest-dot-net>" <youngs-at-konnections-dot-net>


Fellow Experimenters,

I finally found a promising circuit for a Dip Meter (aka grid dip meter in
olden days) that should prove very useful for tuning TCs, determining
inductance, etc.  It uses a most unusual negative resistance oscillator
circuit based on the Lambda Negative Resistance characteristics of a pair of
P & N FETs.  See the complete article:

http://www1.tpgi-dot-com.au/users/ldbutler/NegResDipMeter.htm

What I like about it is that the probe inductor need only be a single coil,
and only a single variable cap is needed.  The frequency range of the unit
described only goes down to 1.6 mHz (160 meter ham band) but by winding a
coil of many more turns, the circuit ought to work at the lower TC
frequencies.

Why use a dip meter?  Because one can determine the Fres of primary or
secondary simply by holding the dip meter coil near them, turning a dial,
and watching for a dip in the meter reading.  No electrical connections
needed.

The article also explains how to use a known value capacitor across an
unknown inductor, then use the dip meter to measure the resonant frequency
to determine the inductance.

I plan to try it.  The only problem is finding variable capacitors.  For the
lower frequencies of TCs, variable caps of several hundred pF would be best.
Might have to cannibalize one out of a cheap AM radio.  If you know of
sources, please post it or email me directly - they are becoming scarce
items.

Thanks,
--Steve Young