In general terms.
Can we say that the variance
of an inductance containing a variometer
is zero to twice the inductance of the rotatable?
The variometer is not talked about much these days
so it is difficult to determine if something
else is at play other than what apears obvious.
I use such a set up in a coupling situation
together with variable physical separation to
prevent kickback and interference from tail
end unused inductance
I am not knoweledgeable enough to understand
all the possible implications so the variometer
seems the best place to start
Regards
Art

"Art Unwin wrote
In general terms.
Can we say that the variance
of an inductance containing a variometer
is zero to twice the inductance of the rotatable?
The variometer is not talked about much these days
so it is difficult to determine if something
else is at play other than what apears obvious.
I use such a set up in a coupling situation
together with variable physical separation to
prevent kickback and interference from tail
end unused inductance
I am not knoweledgeable enough to understand
all the possible implications so the variometer
seems the best place to start.

====================================

The inductance of the two identical coils in series is FOUR times the
inductance of a single coil provided the coupling coefficient between the
two coils approaches unity. It never does.

The main disadvantage of a variometer in a tuned circuit is that as the
mutual coupling and resulting inductance is reduced then the amount of wire
in use remains constant. So the loss resistance remains relatively
constant. And so a VERY low Q occurs at small values of inductance.

No good when used in antenna tuners. Which is great pity. The motion of one
coil rotating inside the other is beautiful to see.
----
Reg, G4FGQ

"Reg Edwards" wrote in message ...
"Art Unwin wrote
In general terms.
Can we say that the variance
of an inductance containing a variometer
is zero to twice the inductance of the rotatable?
The variometer is not talked about much these days
so it is difficult to determine if something
else is at play other than what apears obvious.
I use such a set up in a coupling situation
together with variable physical separation to
prevent kickback and interference from tail
end unused inductance
I am not knoweledgeable enough to understand
all the possible implications so the variometer
seems the best place to start.

====================================


Reg I was not looking just for an answer but better
understanding.
Your 'four times' comment just adds to my confusion.
Are you suggesting that the variometer can cancel
existing inuctance leaving just capacitance?
I suppose that would be one way to increase the variance
that you refer to..
On the subject of tuners, use of the varometer does not
become a efficiency or resistance problem when used in
antenna construction as the relationship of d.c.resisrance
Regards
Art

Note that my net listing is only updated a couple of times
per day so if there are other responses I have yet to see
them so no offence is intended.
I understand that the slowness in updating of the net does
not occur in some places in the U.S.since many responces
appear in concert with the initial posting!


to radiation resistance comes into play.



The inductance of the two identical coils in series is FOUR times the
inductance of a single coil provided the coupling coefficient between the
two coils approaches unity. It never does.

The main disadvantage of a variometer in a tuned circuit is that as the
mutual coupling and resulting inductance is reduced then the amount of wire
in use remains constant. So the loss resistance remains relatively
constant. And so a VERY low Q occurs at small values of inductance.

No good when used in antenna tuners. Which is great pity. The motion of one
coil rotating inside the other is beautiful to see.
----
Reg, G4FGQ

I am not knoweledgeable enough to understand
all the possible implications

--------------------------------------------------

And there it is best to end the matter.

Art Unwin, KB9MZ wrote:
"Are you suggesting that the variometer---?"

I can`t say what Reg had in mind. What he wrote speaks for itself. The
change in mutual inductance between variometer coils causes a change in
their total inductance. As the sense of the rotatable coil can be
reversed, its inductance can be arranged to aid or oppose the inductance
of the fixed coil.

Terman says on page 20 of his 1955 edition:
"when two coils of inductance L1 and L2 , between which a mutual
inductance exists, are connected in series, the equivalent inductance of
the combination is L1 + L2 plus or minus 2M. The term 2M takes into
account the flux linkages in each coil due to the current in the other
coil. These mutual linkages may add to or subtract from the
self-linkages, depending upon the relative direction in which the
current passes through the two coils. Thus , when all linkages are in
the same direction, the total inductance of the series combination
excedes by 2M the sum of the individual inductances of the two coils."

I think Reg gave a reasonable answer. We may assume coupling (mutual
inductance) is high and that the coils are wound for equal inductances.

Now a short-cut. We know that inductance increases with the square of
the turns under common conditions. If we double the number of turns by
sensing the coils so they aid, we will quadruple the inductance, as Reg
said if I recall correctly.

Best regards, Richard Harrison, KB5WZI

Thanks Richard
Your explanation does make sense in that I was looking at
it as several inductors but forgetting the interaction
via coupling.
May I lean on you for further help and education ?
The variometer that I have is a commercial one
and marked 3600-5000 Kc, what ever that means
and the outer windings consist of ten turns on either side
of center.
To make the inductance larger i replicated the original
outer turns so that there is now thirty turns either side
of center.( I added twenty homebrew turns either side to
the original commercial version )
Could you share with me a method of approximating the total
inductance together with its variance values?
Any help would be appreciated.
Regards
Art


(Richard Harrison) wrote in message ...
Art Unwin, KB9MZ wrote:
"Are you suggesting that the variometer---?"

I can`t say what Reg had in mind. What he wrote speaks for itself. The
change in mutual inductance between variometer coils causes a change in
their total inductance. As the sense of the rotatable coil can be
reversed, its inductance can be arranged to aid or oppose the inductance
of the fixed coil.

Terman says on page 20 of his 1955 edition:
"when two coils of inductance L1 and L2 , between which a mutual
inductance exists, are connected in series, the equivalent inductance of
the combination is L1 + L2 plus or minus 2M. The term 2M takes into
account the flux linkages in each coil due to the current in the other
coil. These mutual linkages may add to or subtract from the
self-linkages, depending upon the relative direction in which the
current passes through the two coils. Thus , when all linkages are in
the same direction, the total inductance of the series combination
excedes by 2M the sum of the individual inductances of the two coils."

I think Reg gave a reasonable answer. We may assume coupling (mutual
inductance) is high and that the coils are wound for equal inductances.

Now a short-cut. We know that inductance increases with the square of
the turns under common conditions. If we double the number of turns by
sensing the coils so they aid, we will quadruple the inductance, as Reg
said if I recall correctly.

Best regards, Richard Harrison, KB5WZI

Build the little circuit shown at:

http://www.discovercircuits.com/PDF-...arallelosc.PDF

If you measure the frequency range over which the circuit oscillates,
you can calculate the inductance range of your variometer.

73 Jim AC6XG

Art Unwin KB9MZ wrote:

Thanks Richard
Your explanation does make sense in that I was looking at
it as several inductors but forgetting the interaction
via coupling.
May I lean on you for further help and education ?
The variometer that I have is a commercial one
and marked 3600-5000 Kc, what ever that means
and the outer windings consist of ten turns on either side
of center.
To make the inductance larger i replicated the original
outer turns so that there is now thirty turns either side
of center.( I added twenty homebrew turns either side to
the original commercial version )
Could you share with me a method of approximating the total
inductance together with its variance values?
Any help would be appreciated.
Regards
Art

(Richard Harrison) wrote in message ...
Art Unwin, KB9MZ wrote:
"Are you suggesting that the variometer---?"

I can`t say what Reg had in mind. What he wrote speaks for itself. The
change in mutual inductance between variometer coils causes a change in
their total inductance. As the sense of the rotatable coil can be
reversed, its inductance can be arranged to aid or oppose the inductance
of the fixed coil.

Terman says on page 20 of his 1955 edition:
"when two coils of inductance L1 and L2 , between which a mutual
inductance exists, are connected in series, the equivalent inductance of
the combination is L1 + L2 plus or minus 2M. The term 2M takes into
account the flux linkages in each coil due to the current in the other
coil. These mutual linkages may add to or subtract from the
self-linkages, depending upon the relative direction in which the
current passes through the two coils. Thus , when all linkages are in
the same direction, the total inductance of the series combination
excedes by 2M the sum of the individual inductances of the two coils."

I think Reg gave a reasonable answer. We may assume coupling (mutual
inductance) is high and that the coils are wound for equal inductances.

Now a short-cut. We know that inductance increases with the square of
the turns under common conditions. If we double the number of turns by
sensing the coils so they aid, we will quadruple the inductance, as Reg
said if I recall correctly.

Best regards, Richard Harrison, KB5WZI

Art Unwin, KB9MZ wrote:
"Could you share with me a method of approximating the total inductance
together with its variance values?"

The design of shortwave coils is a complicated process. Skin effect
causes most loss, and single-strand wire wound as a single-layer coil is
usually best. According to Terman, the highest Q is usually, for a given
sized coil, gotten by a winding length somewhat less than the diameter
of the coil. Terman refers to an article in "Wireless Eng.", vol. 26,
page 179, June 1949 by G.W.O. Howe.

My big help with coils comes from the ARRL "L/C/F Calcululator", a
specialized slide-rule. My "Model A" has a price of $2.00 printed on it.

Tom Bruhns has done a lot of work with coils and knows much more about
them than I do. Maybe he will offer some help.

Reg has studied the pertinent factors and used them for some of his
marvelous programs, so he can be a big help.

Sorry I am not qualified to be much help. My method has been "cut and
try".

I was reading an excellent article from a 1920 QST as reprinted in
January 1966, by E.H. Armstrong about his Signal Corps research in WW-1.
He noted that his IF transformers benefitted from many turns of fine
wire which reduced capacitance and added enough resistance to dampen
oscillation tendencies. Armstrong was using "Type 5" triodes in his IF
amplifier of 100 KHz. I am sorry that I am so out of date.

Best regards, Richard Harrison, KB5WZI

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
Regards
Art


(Richard Harrison) wrote in message ...
Art Unwin, KB9MZ wrote:
"Are you suggesting that the variometer---?"

I can`t say what Reg had in mind. What he wrote speaks for itself. The
change in mutual inductance between variometer coils causes a change in
their total inductance. As the sense of the rotatable coil can be
reversed, its inductance can be arranged to aid or oppose the inductance
of the fixed coil.

Terman says on page 20 of his 1955 edition:
"when two coils of inductance L1 and L2 , between which a mutual
inductance exists, are connected in series, the equivalent inductance of
the combination is L1 + L2 plus or minus 2M. The term 2M takes into
account the flux linkages in each coil due to the current in the other
coil. These mutual linkages may add to or subtract from the
self-linkages, depending upon the relative direction in which the
current passes through the two coils. Thus , when all linkages are in
the same direction, the total inductance of the series combination
excedes by 2M the sum of the individual inductances of the two coils."

I think Reg gave a reasonable answer. We may assume coupling (mutual
inductance) is high and that the coils are wound for equal inductances.

Now a short-cut. We know that inductance increases with the square of
the turns under common conditions. If we double the number of turns by
sensing the coils so they aid, we will quadruple the inductance, as Reg
said if I recall correctly.

Best regards, Richard Harrison, KB5WZI

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