From: 	Gary Lau  09-Jan-1998 1058[SMTP:lau-at-hdecad.ENET.dec-dot-com]
Sent: 	Friday, January 09, 1998 10:17 AM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: CHOKES!

>From:   Zuma[SMTP:mwise-at-ns.sosis-dot-com]
>I have finally gotten my 10 lb. spool of 22awg magnet wire in. I
>and planning on winding either a new 6.25 inch coil or an 8.5 inch
>coil. Any suggestiond as to which one I should wind. Also I should have
>plenty of wire to also wind some air core chokes. But is 22awg wire
>adequate to do this with? I also need to know the lowest recommended
>inductance for the chokes?

The minimum choke inductance is probably something that will never be fully
agreed upon.  In addition to differing opinions, it also matters what your
bypass cap (required IMO!) value is and what your operating frequency is.
You want to construct a low pass filter with a high attenuation factor at your
operating frequency, that being Xl+Xc / Xc.  Most coilers use chokes in the
5-100 mH range.

For air core chokes, #22 is too fat.  My 4.25" x 23" secondary is wound with
#22 and yields about 13mH, about the right inductance but absurdly large for
chokes.  Use the thinnest gauge you can find.

I was ultimately unsuccessful using air core chokes.  I had build 7 mH air core
units but they rang and created such arcing to the tank circuit, even with 3K
series damping resistors, that I had to abandon them in favor of powdered iron

Gary Lau
Waltham, MA USA