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



----- Original Message ----- 
From: "T Behler" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, June 05, 2008 2:07 PM
Subject: correctly using Radio Shack RF chokes


> Hi, all.
>
> This is probably self evident, and maybe I've done it the only way 
> possible,
> but could someone tell me how to most effectively use the rectangular 
> Radio
> Shack RF chokes for dealing with RFI?
>
> I guess I'm asking this question basically because my strategy doesn't 
> seem
> to get any results whenever I try it.
>
> What I do is open the top of the choke, wind the wire through the bottom 
> of
> the choke, and then close it up again.
>
> If there's some other way to use these chokes, please enlighten this
> sometimes slow learner.  (grinning widely here)
>
> If you don't recall what the Radio Shack RF chokes are like, they are
> rectangular in shape, with magnets on the inside.  You open the latch on 
> the
> top, and then close it when you're done winding wires around it.
>
> Hope this somewhat convoluted e-mail makes sense.
>
> 73 from Tom Behler:  KB8TYJ
>