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Re: [TCML] Coupling

Hi Doug, Hi Gary,

Doug, you have realized, what was only meant as “my 2 cents”, in my posting, in a perfect way, while I was making only the following kind of “halfwave resonator TC’s”:

on my YouTube channel (hvchbs):
... one can see my small flexible TC, in bipolar=1/2wave & 1/4wave mode:

it has no variable coupling, i.e. of the kind mentioned in my posting
but a description of the “EBM-Museum Bipolar TC” can be had at:

...On the other hand, I made a Twin, the Uni-Bern-Tesla-Twin:
in which the primary is halfed in two flat spirals, positioned below
each of the 2 secondaries, and connected in series. By that way the
coupling can be adjusted for best coupling to each of the secondaries.

In the first of the 2 reports, at page 16 and pp. 18…&…19+ I’ve tried documenting, how one might look at the bipolar TC, in order to calculate it. The way I’ve taken is to assume the symmetry-plane in the middle of the system as a groundplane, and calculating one half of the bipolar only, as an ordinary quarterwave TC, as characterized by Paul Nicholson on TCML:


This view leads to useful results in my case, and also lets me believe the proposed way of adjusting coupling is working –> a fact, Doug has demonstrated. I "think", in this case of a horizontal bipolar, there is no need or advantage for 2 primaries, but only for the secondary cut in 2 halves. I understand and concur with you, Gary, about some detuning of the TC will happen, when moving the 2 secondary halves, in order to change the coupling.

Best regards, Kurt

-----Ursprüngliche Nachricht-----
Von: Tesla <tesla-bounces@xxxxxxxxxx> Im Auftrag von Gary Lau
Gesendet: Samstag, 17. Oktober 2020 01:43
An: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Betreff: Re: [TCML] Coupling

Hi Kurt,

Splitting and separating the secondary seems like a great way to vary the coupling, but one must also bear in mind that doing that will vary the Lsec inductance and tuning.  I can't think of a way to vary only the coupling on a bipolar coil, but I have never built one.

Regards, Gary Lau

On Fri, Oct 16, 2020 at 7:15 AM Kurt Schraner <k.schraner@xxxxxxxxxxx>

> ...just my 2 cents: cutting the bipolar secondary in 2 independently 
> movable halfs could enable the control of the coupling (see the 
> ASCII-sketch):
>                                     oooooooooooo
>     __________________           __________________
>    I__________________I         I__________________I     <---->
>                                     oooooooooooo
> ...the primary can be either of a solenoid or a flat spiral.
>  Regards, Kurt Schraner
> -----Ursprüngliche Nachricht-----
> Von: Tesla <tesla-bounces@xxxxxxxxxx> Im Auftrag von jimlux
> Gesendet: Freitag, 16. Oktober 2020 02:15
> An: tesla@xxxxxxxxxx
> Betreff: Re: [TCML] Coupling
> On 10/15/20 6:50 AM, Douglas Johnson wrote:
> > Thank you both, I think I know where to go from here on my current build.
> > My project is a larger bipolar than I have built to date. Secondary 
> > is
> 3.5"
> > dia. X 24" with .015 mag wire. By the time I built the primary it was 6"
> > long and I was getting "runners" on the secondary. I think my fix 
> > will be going to a flat spiral primary.
> On a bipolar, it's hard to control the coupling on a solenoidal 
> primary sliding it one way or the other doesn't change the flux 
> distribution very much.
> I'm not sure a flat is any better.
> _______________________________________________

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