Inductances etc..

[ivconic]

Ok.. i have question;
trying to make cc coil for TGSL. Inductances are known: 6mH for TX and 6.5mH for RX.
How to calculate no of turns for cancel coil?
Dimensions of TX and RX are not exactly convenient. TX should be wounded on 21cm former and RX on 15cm former!
So..i made 6mH TX coil on 21cm former and 6.5mH RX coil on 15cm former. Than i started to wound cancel coil over RX coil but in oposite direction from TX (and RX). Some 70 windings. Start of cancel coil connected to end of TX coil. Measured inductance now is 5.6mH !? Than i removed some 20 turns from cancel coil and measured inductance was 6.01mH. Connected on TGSL giving terrible results; residual voltage is 5.5V !!! Than also removed 20 turns and measured inductance was 5.8 mH !? No way out!
Than i made another test. Removed whole cancel coil from former setup. Now i have TX 6mH and RX 6.5mH, right? Connected in serie but keeping same direction (end of TX to start of RX) i measured 16.5mH !!! Than reversed pins and connected those in oposite directions (end of TX to end of RX) and i measured 8.7mH !!
So...you see what i mean!?
Question is; how to calculate two coil inductances connected in serie (TX + oposite direction Cancel coil) to finally give wanted 6mH inductance...AND to maintain "canceling" condition?
TGSL needs exact TX inductance (6mH) to work exactly as projected.
So... i assume that TX coil should be wounded to give approx 8-10mH and than adding Cancel coil, overall inductance would fall to some 6mH...
But i hate to guess and blindly experiment much. I want to establish rules and calculations.
Most probably all infos can be found on internet. I tried without much of success. Don't have good ideas about keywords to use with Google.
I tried with "reversed polarity serial inductances.." or simillar. No results.
So... what we need here is how to calculate overall inductance of two inductances connected in serie BUT with reversed polarities.
Any ideas?

[ivconic]

There is way out; calculation that includes area covered by TX and RX coils. Relation between those two areas could give clues about Cancel coil. But calculations i have seen so far are not accurate at all.
What is most important here is to calculate Cancel coil BUT that coil will also affects TX inductance (and working frequency too). On given example we have 6mH as final TX inductance....

[Qiaozhi]

Making a concentric coil is extremely tricky and fraught with problems. The ratio of the areas under the TX and RX coils can be used to get an approximation of the number of turns required on the nulling coil, but it is not very accurate. Also, when the TX coil and nulling coil are in series, the inductances add. They do not subtract.

You can use the Coil Calculator to play around with the values and get a starting point for experimentation, but it's not easy. The positioning of the nulling coil is also very sensitive. It's a lot easier to make a DD or omega coil.

Please don't let me put you off making a concentric, but I would have the 5Kg hammer standing by.

[ivconic]

Making a concentric coil is extremely tricky and fraught with problems. The ratio of the areas under the TX and RX coils can be used to get an approximation of the number of turns required on the nulling coil, but it is not very accurate. Also, when the TX coil and nulling coil are in series, the inductances add. They do not subtract.

You can use the Coil Calculator to play around with the values and get a starting point for experimentation, but it's not easy. The positioning of the nulling coil is also very sensitive. It's a lot easier to make a DD or omega coil.

Please don't let me put you off making a concentric, but I would have the 5Kg hammer standing by.

"...Also, when the TX coil and nulling coil are in series, the inductances add. They do not subtract..."

I agree. But i measured different than that? I just bought brand new inductance meter. The inductances add when in serie in same direction. But when in oposite direction than it seems the inductances are giving something else? (Keep in mind that those 2 inductances are sharing same former, one on 21cm and another on 15cm diamms)
I can involve effort and by using trial and error method to achieve to make this one cc coil for TGSL. But it is not what i am up to. I don't exactly need one cc coil for TGSL. I need understanding and clarifications about inductance relations when connected in serie; in same and in oposite directions. A method. Proper and accurate method. That's what i need.
Cheers!

[ivconic]

Or focus just on this:

Same former/holder with two circles (channels), one 21cm and another 15cm.
Ok.
On 21cm there is 6mH coil and on 15cm ther is 6.5mH coil.
*Connected in serie in same direction (end of TX to start of RX) those are giving 16.5mH.
*Connected in serie in oposite direction (end of TX to end of RX) those are giving 8.7mH.

See?

[WM6]

*Connected in serie in same direction (end of TX to start of RX) those are giving 16.5mH.
*Connected in serie in oposite direction (end of TX to end of RX) those are giving 8.7mH.

See?

Those results from inductivity formula in which we have product of two squares:

d2 x n2
------------- = L(uH)
18d + 40l

where:

L = inductance in micro henrys
d = coil diameter in inches (from wire center to wire center)
l = coil length in inches ( 1 inches = 25.4 mm)
n = number of turns

in practical calculation used from page:
http://www.hamradioindia.com/HRI-Calc/AIRCoils.html

we get results:

Number of turns - Inductance (nH):
3 - 77
4 - 122
5 - 177
6 - 240
7 - 306
8 - 379
9 - 470
10 - 582
11 - 644
12 - 656
13 - 745
14 - 789

So we can stated by 3 turns inductance of 77nH, but by 6 turns we do not get double as much (154nH) but about triple as much 240nH and so on. There is no simple (+-) linearity between turns and inductance.

Therefore is not a simple linear interpretation of the successive joining of two coils with a variable polarization.

So this (lower) formula can be interpreted (according wiki)



that these simple relationships hold true only when there is no mutual coupling of magnetic fields between individual inductors.

Maybe Aziz can simulate this problem and represent results graphically.

[ivconic]

"...There is no simple (+-) linearity between turns and inductance..."

Yes it is fact.
But here problem is even more complex. 2 coils with certain inductances, put togather in space with some relative relation to each other, and connected in serie are giving third inductance. How to calculate (predict) that third inductance? Even more complex; those 2 inductances in serie will give different third inductance depending on polarities. Are coils placed with windings in same direction or those are placed in oposite direction - not the same result at the end.
Is there any calculation for serial cuopling inductances? Serial coupling where coils are wounded in same direction and serial coupling where coils are wounded in oposite direction...

[WM6]

How to calculate (predict) that third inductance? Even more complex; those 2 inductances in serie will give different third inductance depending on polarities. Is there any calculation for serial cuopling inductances?

Not only of polarities but depend on level of mutual coupling of magnetic fields between individual inductors. (I added some obout serial inductance in my previous post).

Problem is that this level of mutual coupling of magnetic fields between individual inductor is hard to define or set (not like tighten turns).

Simple formula
Ltotal= L1+L2+ ...Ln is valid only for non mutual coupled (by magnetic field) serial inductor. On other site number of mutual coupling levels (by magnetic field) can be countless. So there is no easy calculation for such hard to define configuration.

[ivconic]

I tried to draw the situation. Former used here is taken from scraped Garrett GTI coil. Looks something like this.. ( Showing "Mutual coupling" effect between 2 coils on setup)

[ivconic]

Not only of polarities but depend on level of mutual coupling of magnetic fields between individual inductors. (I added some obout serial inductance in my previous post).

Problem is that this level of mutual coupling of magnetic fields between individual inductor is hard to define or set (not like tighten turns).

Simple formula
Ltotal= L1+L2+ ...Ln is valid only for non mutual coupled (by magnetic field) serial inductor. On other site number of mutual coupling levels (by magnetic field) can be countless. So there is no easy calculation for such hard to define configuration.

Tell me something about it!
That's why i started this thread after all.
But i presume there must be the known method to calculate exact needed inductions as for given setup.
How they calculated it at the first place? At White's, Fisher, Minelab, Garrett...??
For example i would take any concentric White's or Fisher coil...
How to calculate Cancel coil for some White's (or Fisher) concentric coil?

[ivconic]

Here is the photo of mentioned setup...

[ivconic]

"Mutual coupling" is the right term here! WM6 you are right there.
So... how to calculate Cancel coil ( connected in serie with TX coil and wounded over RX coil ) for this setup and at the same time to maintain 6mH inductance of TX coil keeping im mind "Mutual coupling" effect between TX coil and Cancel coil.

[WM6]

But i presume there must be the known method to calculate exact needed inductions as for given setup.

All can be calculated by given data. You havent data for mutual coupling level of magnetic fields of both inductor. Maximal coupling level we can find by tighten turns on one coil where inductance is not linear depended on Nr. of turns. By two coupling coils you change many parameters at same time not only coupling level, but inductance of both coils, parasitic capacitance, Q, Z, resonance... And all this by only small movement. By changing position everything given data changes in the unknowns. But you want to calculate from unknown data? Like labs do.

How labs do such things? All can be reversed, formula too. Labs do first some targeted and sistematic tests and measurement (see table in my first post) then do some calculations and simplified aplicative formulas.

But you do not have patience to do sistematic tests and measurement. Do you?

[ivconic]

All can be calculated by given data. You havent data for mutual coupling level of magnetic fields of both inductor. Maximal coupling level we can find by tighten turns on one coil where inductance is not linear depended on Nr. of turns. By two coupling coils you change many parameters at same time not only coupling level, but inductance of both coils, parasitic capacitance, Q, Z, resonance... And all this by only small movement. By changing position everything given data changes in the unknowns. But you want to calculate from unknown data? Like labs do.

How labs do such things? All can be reversed, formula too. Labs do first some targeted and sistematic tests and measurement (see table in my first post) then do some calculations and simplified aplicative formulas.

But you do not have patience to do sistematic tests and measurement. Do you?

I do have patience for this things. Besides...it is winter time, i have plenty of time to do such things.
Problem is that i dont have lab!
Was thinking to hear other opinions here, might be some help from those.
Otherwise i know my deal; trial&error and lot of trivial things to do!

Like i said: it is not my goal to make one cc coil for this particular TGSL. Real goal would be to learn and fully understand principles! Right thing!

[WM6]

"Mutual coupling" is the right term here! WM6 you are right there.
So... how to calculate Cancel coil ( connected in serie with TX coil and wounded over RX coil ) for this setup and at the same time to maintain 6mH inductance of TX coil keeping im mind "Mutual coupling" effect between TX coil and Cancel coil.

I think there not only question of simple inductance formula. Probably lab started from TX stage and defined here all: best circuit and adequate TX coil. Then they define RX stage: best RX circuit and adequate RX coil. Next step is coupling both stage (coils) togheter and reverse corrections of previous step. I think there is no primary formula and calculate question, but question of hard lab work (sistematic lab test and measurements). From results they can calculate simplified aplicative formulas for future needs and use.