# Re: 1/4 Wave, etc.

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From: 	Alfred A. Skrocki[SMTP:alfred.skrocki-at-cybernetworking-dot-com]
Sent: 	Thursday, September 11, 1997 1:09 AM
To: 	Tesla List
Subject: 	Re: 1/4 Wave, etc.

On Thursday, August 28, 1997 10:36 AM Pete Demoreuille
[SMTP:pbd-at-cybernex-dot-net] wrote;

> Maybe someone could help me out - I am complete confused as to
> what makes a 1/4 Wave coil a 1/4 Wave coil - What special things
> must be considered?  And the same for 1/2 Wave coils...
> -I guess there must be an advantage with these two types of coils,
> like ?

Hi Pete, a 1/4 wave coil is a coil such that the length of the wire
wrapped around the form is 1/4 the resonant frequency of the
finished coil. The reason for using a 1/4 wave length coil is
illustrated bellow in the crude ASCII drawing.

*
*      *
*            *
*----------------*------------------*
|        |       |  *      |      * |
| <-1/4->|       |     *   |   *    |
|                |         *        |
| <--- 1/2 --- > |         |        |
|                          |        |
| <-------- 3/4 ---------> |        |
|                                   |
| <-------- 1 wave length --------> |

You see at the 1 wave length and 1/2 wave length points the voltage
is 0, while at the 1/4, 3/4, ect. points it is at a maximum. Since we
strive for the largest output on our coils, we endeavor to make them
1/4 wave length long. It is not too wise to use a 3/4 wave length
coil since this will invite coronal break out on the side of the coil
ultimately damaging the windings.   The 1/2 wave length coils are
only good if they are center feed (primary over the middle thus
forming two 1/4 wave length coils connected at the middle) here you
have maximum voltage at the two ends. This format is not too good
when you get to the larger coils since it becomes very difficult to
mount the coil without inviting discharges to ground. In the early
1900's , when 1/2 wave length coils were popular, it was thought that
the 1/2 wave length center fed coils would have twice the output as a
1/4 wave length bottom feed coil but in practice this is not the case
and this is why you rarely see this design today. BTW it is not as
easy to make a coil 1/4 wave length as it would seem! There are many
factors that alter the resonant frequency of the coil and these are
very difficult to account for before the coil is actualy wound, but
when it is achieved the results are usually spectacular! The most
important of these factors is the combined distributed capacitance of
the finished coil and it's top terminal. Equations are available to
accurately calculate each of these but as of yet no formula has been
able to correctly predict their combined effect. Many of us are
working on this problem and a good equation should be available very
soon.

Sincerely

\\\|///
\\  ~ ~  //
(  -at- -at-  )
-----o00o-(_)-o00o-----
Alfred A. Skrocki
alfred.skrocki-at-cybernetworking-dot-com
.ooo0   0ooo.
-----(   )---(   )-----
\ (     ) /
\_)   (_/

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