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

```---------- Forwarded message ----------
Date: Tue, 17 Jul 2007 01:36:02 +0200
From: Finn Hammer <f-h@xxxx>
To: Tesla list <tesla@xxxxxxxxxx>
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 <n_alstrup@xxxxxxxxxxx>
> 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
> 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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