Hi Steve,
I just ordered the 1/2" ID ferrite split beads.  Though the site doesn't 
mention the ferrite mix, one of the other beads mentions mix 43 and that is 
the one I'm looking for.  Thanks for the heads up on this!
73
Bob Tinney, [log in to unmask], K8LR
Skype Name, bobtinn
Live Long and Prosper!

----- Original Message ----- 
From: "Steve Forst" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, June 05, 2008 4:05 PM
Subject: Re: correctly using Radio Shack RF chokes


Hi Tom,

Not wanting to correct the professor, but for what it's worth,  they are not
magnets, although they  have magnetic properties.  They are made of ferrite,
which is  a ceramic that has iron mixed in.  As someone said there are
various "mixes" which  would have  differing properties  suitable for
different frequencies.  You would need to worry about the different mixes if
you were building a balun  and needed to cover a particular freq.  Shouldn't
be a big deal when doing rfi stuff.

You are doing it correct.  I don't understand the math behind it, but  every
turn of the wire through the core increases the choking by  the square root
of something or other, so the more turns the better.

Other (cheaper) sources besides RS are Amidon, and Fair-rite.  Another
source I've used is:

http://www.allelectronics.com/make-a-store/category/235/Ferrites/1.html

These are slightly different, in that  you open the plastic clamshell and
lay the wire in like putting a hot dog in a bun and then close the plastic
shell.   Different sizes for different cables, or use a larger size and wind
the cable several times.

When running 600 watts on 160 I was getting some  sounds from the internal
keyer in my headphones, while not using that keyer.   Some trial and error
and found that clamping  one on the 12 v  line from power supply to rig
cured it.

73, good luck Steve KW3A