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# Re: Resonant frequency of twin coil? (fwd)

```---------- Forwarded message ----------
Date: Tue, 17 Jul 2007 09:00:27 -0500 (CDT)
From: Gerardo Lezcano <lez_gera@xxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Resonant frequency of twin coil? (fwd)

Some time ago, I connected a small signal generator to a primary coil.  On the secondary, a small topload on the high side and another "tertiary" coil on base of the secondary, no ground connection.  Two antiparallel LEDs in series with secondary and tertiary.  Another topload on high end of tertiary.

With this arrangement, found the resonance frequency, LEDs glowing dimly.  Then, I connected the middle point between secondary and tertiary, to ground.  LEDs went off, as they were connected now between the tertiary base and ground.

Questions:

An ungrounded bipolar (twin) secondary has the same resonance frequency as a middle-pointed-ground-connected identical secondary?

I think, because LEDs went off, that Earth "forces" a voltage node on base of each coil.  This changes the resonance frequency.  Then the signal generator is no longer feeding correct frequency to light the LEDs.

If we could find the new resonance frequency for this two-coil system, there will be again a voltage node on base of each coil?

If we find the new resonance frequency, what is the maximum distance we could separate the coils and still getting a resonance between them?  Remember, we have a primary coil feeding a near secondary connected to ground.  At a distance, an unpowered tertiary.

While we are feeding the secondary, and the distant tertiary is glowing its base LEDs, maybe we will find a voltage node on each coil's bases.  If so, what is the speed of the currents in the soil between them?

Gerardo.

Tesla list <tesla@xxxxxxxxxx> escribió:

---------- Forwarded message ----------
Date: Tue, 17 Jul 2007 01:36:02 +0200
From: Finn Hammer
To: Tesla list
Subject: Re: Resonant frequency of twin coil? (fwd)

Nicolas.

Your resonant frequency in the tank is the same as the secondary res. freq.

Keep in mind that the primary inductance is divided in 2, so that 1/2 is
in each primary coil. This means that each primary coil should have 1/2
the total inductance.
There is going to be some inductance in the wires between the tanks
also, so my guess is that the coils woll tune with around 3,5 - 4
primary turns.

Whereabouts do you live? I`m in the Hobro area.

Cheers, Finn Hammer

Tesla list skrev:
> ---------- Forwarded message ----------
> Date: Mon, 16 Jul 2007 08:20:07 +0000
> From: Nicolas Alstrup
> To: tesla@xxxxxxxxxx
> Subject: Resonant frequency of twin coil?
>
> Hi,
>
> I havent been able to find any information on this on the web.... I am in
> doubt how to calculate the resonant frequency for a twin coil, or rather how
> to tune it - any help appriciated....
>
> This is my schematic:
> __ __
> / \ /
> \
> \__/ \__/
> | |
> -------------------------------------| |-----------|------------------- |
> | | cap | | | |
> | | c c c c
> o o c c c c
> HV in spark gap c c c c
> o o c c c c
> | | c c c c
> | | | | | |
> ----------------------------------------------------|------------------- |
> |_____________|
>
> And these are my specs:
> Secondary coil:
> Each SC consist of apprx. 780 turns of 0,315mm wire. Diameter 60mm, height
> 270mm
> Calculated selfcapacitance= 4,282pF
> Top load: Sphere, radius 120mm, calculated C=13,466pF
> Calculated resonant frequency for each coil: 444,257 kHz
>
> Primary circuit
> HV input, NST: 8000V , 50mA
> MMC capacitance: C=0,0204uF
> Flat Helical coil: inner diameter: 70mm, Wire diameter: 2mm, wire spacing:
> 1mm
>
> My question now is: How many turns on each primary coil? Should I just
> calculate the resonant frequency as if there were just one secondary and aim
> at 444,257 kHZ (that is around 7 turns) or how to do it?
>
> Thank you very much for any help,
>
> sincerely Nicolas Alstrup
>
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