TGSL coil query

[samsearcher]

Just testing the TGSL board and wound the first 'D' coil following the info from TGSL 101 revision 07-29-2012 by Don Bowers.

Using the former and wire dimensions (0.25mm) as specified, (coil constrained with dental floss but not screened or epoxied)
the first half coil came out at 23.9 Ohms 5.94 mH
The frequency at the coil is 13.94 kHz when running in the Tx position

I wound a second coil with more turns than should be needed (115T)
Resistance 25.9 Ohms, Inductance 7.4mH but frequency 12.99 kHz when running in the Tx position

I'm puzzled why the frequency is lower ?
What should I be aiming for? 6.0mH & 6.5mH OR running frequency

P.S the -5V rail is nearer 6.5V

THANKS!

[kt315]

I'm puzzled why the frequency is lower ?
---
bigger inductance gives lower frequency, if we take cap tank is constant.

[samsearcher]

thanks, yes of course! so should I be trying for perfect inductance OR exact frequency?

[kt315]

inductance is only some value or estimate. it is not so important if be honest. VLF coil is simple transformer
with very poor link between windings itself (no big discovery here). so MORE IMPORTANT HERE is the coefficient of transformation as
main characteristic of any transformer.

you see - NO Ohms, NO mH. I DO NOT USE THEM. why people like to use its... i do not know.

[manhunt47]

Just testing the TGSL board and wound the first 'D' coil following the info from TGSL 101 revision 07-29-2012 by Don Bowers.

Using the former and wire dimensions (0.25mm) as specified, (coil constrained with dental floss but not screened or epoxied)
the first half coil came out at 23.9 Ohms 5.94 mH
The frequency at the coil is 13.94 kHz when running in the Tx position

I wound a second coil with more turns than should be needed (115T)
Resistance 25.9 Ohms, Inductance 7.4mH but frequency 12.99 kHz when running in the Tx position

I'm puzzled why the frequency is lower ?
What should I be aiming for? 6.0mH & 6.5mH OR running frequency

P.S the -5V rail is nearer 6.5V

THANKS!

Of course, this is very simple and quite obvious.
Since you connected to an oscillator circuit once, you connected the Rx coil and then the TX coil. And since the amount of inductance of this coil varies, the output frequency of each one also varies.
And as you tested yourself, the higher inductance coil produces fewer frequencies that can be calculated from the following equation.

[samsearcher]

Thanks, but I am getting slightly lower inductance than needed (first TX coil) 5.9mH instead of 6.0mH, and lower frequency 13.9kHz instead of 14.5kHz...?
So to raise the frequency (if needed?) I would need to reduce the inductance still further.....or adjust the tuning caps?
This is assuming my inductance and frequency meters are reasonably accurate.....

OR should I just carry on and get both coils close and see it the null OK?

[dfbowers]

If you are following the pattern in the document, I have found that as long as the RX coil has about 5 more turns than the TX coil (in the 100 turn range) the TGSL should tune up OK.

[samsearcher]

Thanks all, seems like it's getting there with tweaking the coils.

Is there anyone on the Forum in the UK, who's willing to make me a couple of coil shells?...... before I 'bite the bullet' and build a vacuum table and formers.

[manhunt47]

Thanks, but I am getting slightly lower inductance than needed (first TX coil) 5.9mH instead of 6.0mH, and lower frequency 13.9kHz instead of 14.5kHz...?
So to raise the frequency (if needed?) I would need to reduce the inductance still further.....or adjust the tuning caps?
This is assuming my inductance and frequency meters are reasonably accurate.....

OR should I just carry on and get both coils close and see it the null OK?

In the case of the TX winding, the most important thing is that you reach the desired frequency, and now this does not matter when changing the capacitance or coil inductance.
So, you can create the correct TX frequency using the capacitor or inductance.
And the more important thing is the RX coil, which has to be precise and the coil should be adjusted correctly(nulling).

[samsearcher]

Something weird going on here! my Tx coil has been epoxied, mylar screened and taped and is fine I think (just over 6.0mH)
The Rx coil that seemed OK at 6.5mH before I coated in epoxy, is now reading 11.2mH ! (not yet screened)

[kt315]

mylar? https://www.sosproducts.com/v/vspfil...tos/2502-2.jpg

[samsearcher]

I am reading TX frequency at the Clock input pin 1 of U100 = 13.76KHz,
if I read across coil directly = 14KHz (due to meter cap?)

[manhunt47]

Something weird going on here! my Tx coil has been epoxied, mylar screened and taped and is fine I think (just over 6.0mH)
The Rx coil that seemed OK at 6.5mH before I coated in epoxy, is now reading 11.2mH ! (not yet screened)

Specify the type of epoxy you used to determine the reason for the sharp increase in the Rx coil inductance.
This shows you are making a mistake

[samsearcher]

I think I must be picking up Radio 4 or something! The resistance is still OK at around 24 Ohms. My inductance meter sometimes reads a coil as a straight resistor, rather than an inductor, so that doesn't help either. I'm just assembling all to see what works and what doesn't in practice.
Still waiting on some coil housings though..... (Eric )

[Hyena]

I think I must be picking up Radio 4 or something! The resistance is still OK at around 24 Ohms. My inductance meter [ATTACH]45712[/ATTACH] sometimes reads a coil as a straight resistor, rather than an inductor, so that doesn't help either. I'm just assembling all to see what works and what doesn't in practice.
Still waiting on some coil housings though..... (Eric )

Do not measure inductance with these testers. For example this T4 ESR meter: https://www.google.com/search?q=LCR-...w=1767&bih=827
Measure inductance well only around 1mH. When I measured 14,7mH (and it was precise), T4 measured 19mH.

Build oscilator, measure tank circuit capacitor precisely with multimeter and calculate inductance from frequency (with freq counter or oscilloscope). Its much more reliable measurement. Do not trust these testers, its only good to check if transistor is failed completely or not, do not trust numbers from these devices!