# 1/4 Wave and Secondaries

• To: tesla-at-grendel.objinc-dot-com
• Subject: 1/4 Wave and Secondaries
• From: richard.quick-at-slug-dot-org (Richard Quick)
• Date: Thu, 7 Sep 1995 18:39:00 GMT
• >Received: from ns-1.csn-dot-net (root-at-ns-1.csn-dot-net [199.117.27.21]) by uucp-1.csn-dot-net (8.6.12/8.6.12) with SMTP id NAA09103 for <tesla-at-grendel.objinc-dot-com>; Thu, 7 Sep 1995 13:47:14 -0600

``` * Original msg to: usa-tesla-at-usa-dot-net

Quoting "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>:

> Re the discussion on secondaries with Graham A. and others...

> I last night designed three coils to illustrate the points I am
> seeking answers to regarding 1/4 wavelength of wire, etc.
> Here is the analysis.

> I arbitrarily chose a design frequency of 200kHz for the coils. The
> formula I am using to calculate Cself and L are well tested and have
> worked for dozens of real designs (by way of illustration, Greg Peters
> yesterday sent me data for his coil and told me that its resonant fre-
> quency was "about 200kHz" - My calculations gave a figure of about
> 210kHz - this to give an idea of accuracy)

> All measurements in inches :

>        Winding Height   Diameter    Turns   Wirelength  L(mH)   C(pF)
>        **************   ********    *****   **********  *****   *****
> Coil1     24              12         583     22000       41.7    15.2
> Coil2     24               8         932     23400       51.1    12.4
> Coil3     15              15         374     17600       36.2    17.5

> Note that LxC is the same in all cases!

> According to wavelength = v/c : -at- 200kHz  wavelength = 1500 metres
> 1/4 wavelength = 375 metres
> = 14760 inches    c.f. figures for actual coils

> Leaving aside winding clearance from the ground, which of the three
> coils is the best for a T.C. (after adding a terminal of course which
> will lower the frequency by the same amount in all cases) ?

OK, Monty (Monty Hall was a big game show host here in the 'states)

I'll take door, er coil, number two!

Number two has the highest inductance. Inductance is critical to a Tesla
secondary. If you notice this coil also has the highest inductance per
unit volume of the three coils.

Number two also has the best aspect ratio. In order to sucessfully couple
the high inductance secondary coil to a large primary (more uniform ex-
citation) you want a coil that will be approximately the same height
as the primary diameter.

Number two also has between 800 - 1000 turns on the coil. It fits all
of my guidelines for a high performance secondary coil.

BTW, I have a coil nearly exactly like coil number two it sitting right
here. It IS a phenomenal performer.

Coils number one and three will mkae decent secondary coil for Tesla
Magnifier systems.

Richard Quick

... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12

```