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.
You have no need to be sorry!
\You are trying to help me and
I appreciate that.
My problem started when I moved
away from a homebrew coil on a circuit
which was coupled to a rod ( distributed inductance)
The coupled rod when moved allowed for
an ideal matching setup
as it could be made into a perfect match
for top band use.( the rod was the driven element)
When I substituted a variometer for fine
tuning everything went to pot!
(That is why they call mesh circuits 'complex' )
Thus the questions regarding variometers
and the markings. With the new band in
the U.K. being used I suspect we are going
to hear a lot more about this instrument
and I can then reintroduce it on my antenna
Best regards
Art




(Richard Harrison) wrote in message ...
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