What a great posting!
The input and work has not gone unnoticed
and I am sure that all on the net appreciate
your presence. I need time to digest it as I
am now in a state of confusion regarding the subject
and its applicability to my particular project.
Many, many thanks for your effort
Art





(OK1SIP) wrote in message . com...
Hi Art,
the connection "all in series" is the proper one, not "particular".
Usually there are four parts of winding: one half of fixed coil, two
halves of moving coil and another half of fixed coil. Let's mark the
fixed coil inductance L1 and the moving coil L2. The construction is
made so that L1=L2 and magnetic coupling is as tight as possible. The
mutual inductance when both coils have the same axis is therefore
approximately M=L1=L2.
If the moving coil is turned so that the magnetic fields add, the
total inductance is (nearly) L = L1+L2+2M = 4*L1.
If the moving coil is turned so it is perpendicular to the fixed one
and the magnetic fields do not influence the other coil, the mutual
inductance is zero and the total inductance is L = L1+L2 = 2*L1.
If the moving coil is turned so that the magnetic fields subtract, the
total inductance is (nearly) L = L1+L2-2M = 0.
When you added some turns, you destroyed the construction symmetry.
Measuring the total inductance at various coil positions within 0..180
deg and at the working frequecy is the best you can do.

Variometers are often used for tuning antennas at 136 kHz. See
http://www.sweb.cz/ok1fig/Small_vario.jpg ,
http://www.sweb.cz/ok1fig/Big_vario_02.jpg ,
http://www.sweb.cz/ok1fig/Big_vario_03.jpg or
http://www.g0mrf.freeserve.co.uk/variometer.htm .

BR from Ivan


(Art Unwin KB9MZ) wrote in message om...
Richard,
On reflection I now see that how a variometer is
connected up can make a big difference.
In my particular case all coils are connected in
series such that the current is constant thru out.
An alternative way of connecting a variometer I suppose
is to supply a different current or placing the revolvable
inductance as part of another separate circuit whereas the
COUPLING action alone will provide the variances you speak of.
As for adding inductances in series, as stated in my earlier
reply, is a lot different such that I now believe my
original analysis is correct.( In other words I have just
increased the number of turns by sliding the inductances
together to make one inductor leaving the third inductor
which is revolveable seen as an inductance with reversable
turns or flux pattern.)
As you probably can now see I am totally confused,
especially since this arrangement is then coupled
to another separate circuit which is where I suspect the
+ or - 'M' variation comes into play comes into play.
Regards
Art