Concentric coil for Sovereign Elite

[Melano87]

Hi,

I would like to make a concentric coil for my Sovereign Elite.
For the base I have a body of a 9" coil.
Can you explain to me what I need, the necessary circuits etc.
I understood that it was very difficult to make (balance).

Thanks.

[kt315]

you need an preamp inserted... my project to give the board was stopped... while at end.

[Melano87]

Ok, I have this schematic.

[Melano87]

Hi,

I have read all the threads on the forum, I have many questions :

Concentric coil

Need Tx : 1.01 / 1.02uH - R < 2 Ohms and Rx : 0.44 / 0.46 uH - R = 5 Ohms

I calculate for the my coil (with coil calculator)

Tx : 41 turns - 0.8mm wire - 0.992 mH (I think the value will go up a bit during construction) - 1.018 Ohms

Rx : 36 turns - 0.25mm wire - 0.422 mH (I think the value will go up a bit during construction) - 4.473 Ohms

Bx : 10 turns - 0.25mm wire - 0.037 mH - 1.2425 Ohms (the value mH will subtract of Tx, if I understood correctly)

Questions :
- For the resistance of Rx, it is better to be above or below (closer to 4 ohms or 6 ohms)?
- I have to put in series the loop Bx (which "cancels" Rx) and the mini loop to cancel the PCB of the amp ?
- For Bx, its value in ohms will be added to Tx, thus leading me to be above the 2 ohm "limit". Can I use a wire of the same diameter as Tx (which will allow me to lower Ohms)?

Amp

- I have seen several assemblies on the forum and elsewhere (with or without the 6uF capacitor on Tx, with or without transistors, 560 Ohms by 750 Ohms...).
But this diagram if I remove the capacitor on Tx, and change the resistor of 560 Ohms by 750 Ohms) is viable?
- Do 1N4148 type diodes go for bridge rectifier?
- For SMD tantale capacitors, 10V 33uF is good or 16V ?

Thanks.

[Melano87]

To add or else I increase the diameter wire of Tx to 1mm (0.944 mH - 0.678 ohms).

An additional question, on the super PDF explaining the construction of a concentric coil (TGSL), it was talked about that if the ratio between the diameter of Tx and Rx is 1/2, the number of loops of Bx must be 4 times sless important than that of Tx.
The diameter of the Bx wire must be the same diameter as Tx or Rx?

[Carl-NC]

Questions :
- For the resistance of Rx, it is better to be above or below (closer to 4 ohms or 6 ohms)?

Usually RX resistance is not all that critical. A delta of 1 or 2 ohms due to the RX coil is well within the usual tolerance of the 560Ω resistor.

- I have to put in series the loop Bx (which "cancels" Rx) and the mini loop to cancel the PCB of the amp ?

Not sure how the mini loop cancels the PCB, unless it creates a field null at the PCB. If so, they are both in series with the TX coil.

- For Bx, its value in ohms will be added to Tx, thus leading me to be above the 2 ohm "limit". Can I use a wire of the same diameter as Tx (which will allow me to lower Ohms)?

Yes.

- I have seen several assemblies on the forum and elsewhere (with or without the 6uF capacitor on Tx, with or without transistors, 560 Ohms by 750 Ohms...).
But this diagram if I remove the capacitor on Tx, and change the resistor of 560 Ohms by 750 Ohms) is viable?

I don't know what the 6uF cap is for, it seems to me it will mess up the TX waveform. I wonder if it is a mistake. A 750Ω resistor will alter the tau of the RX coil but I don't know how much that matters.

- Do 1N4148 type diodes go for bridge rectifier?

That will work.

- For SMD tantale capacitors, 10V 33uF is good or 16V ?

Whatever the DC voltage is, I would use a rating of 50%-100% higher. Probably 10V is fine.

- An additional question, on the super PDF explaining the construction of a concentric coil (TGSL), it was talked about that if the ratio between the diameter of Tx and Rx is 1/2, the number of loops of Bx must be 4 times sless important than that of Tx.
The diameter of the Bx wire must be the same diameter as Tx or Rx?

Normally the Bx wire gauge is the same as the TX coil.

[Altra]

You have a lot of questions. Many can only be answered by trial and error.

The ".6uf" capacitor in the drawing is a mistake. It should be 620pf or 680pf.

The diodes can be 1N914,1N4148 or BAT85's

Your capacitors should be 16v or greater.The tx is 10v pp.

The 560 ohm serves as damping resistor for the receive coil. This can be adjusted depending on your RX coil.

The Soverign is technically not a PI, but has simularites. It has a broadband frontend, no filtering, fast preamp and damping.

Here's a good guide for building a concentric coil for PI.

https://www.geotech1.com/cgi-bin/pages/common/index.pl?page=metdet&file=/projects/coplanar/index.dat

Add: Looks like Carl answered while I was writing

[Carl-NC]

The tx is 10v pp.

Seems like this will create +/- 5V for the preamp.

[Altra]

Seems like this will create +/- 5V for the preamp.

Yes, the ground wire (pin3) is vref or 1/2 the tx voltage

[Melano87]

Thanks for your answers Carl and Altra.

So I change the 6uF capacitor to a 620pF. I leave the resistance to Rx on 560 ohms.
I will redo my calculations for Tx and Bx using the same wire diameter.

Yes, I consulted the "Coplanar" and "Concentric coil TGSL" guides, Fortunately, they exist (laughs).

We agree that Rx is a different wire diameter is not a problem?

[Carl-NC]

Typically the TX wire is a heavier gauge to minimize TX current-to-voltage phase shift error¹ and to minimize power loss. Even though the Sov TX is not sinusoidal you still want to minimize the TX exponential error¹. At higher frequencies you would even use Litz in the TX.

Most concentric coils use the same wire for the BX as for the TX. You don't have to, but it's easier.

The RX coil is less critical for resistance because it tends to be loaded lightly. So a smaller gauge wire is fine. I doubt that it's all that critical to make sure it's 5Ω.



¹ It's not so much the error that matters, but rather the variation over temperature. It messes up the GB.

[kt315]

hi all hi M87...

sure i can not give direct links on SPRINT LAYOUT because pirate version... will be immediately deleted by moderator (those cases had been).
so PLEASE seek it in YOUR sector of Global Net. i believe it is francuas -? i took it from russian zone of the net, sure do not know what are in english... not living in... english is not my native...

ok. i just SHOW you what you HAVE TO SEE,

[kt315]

SP 6 for scale of a PCB... scaled and ready to copy... just as an example of using.

[kt315]

[kt315]

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