🚀 go-pugleaf

>Brian Carey 283-4181 (careyb@dallas.jsc.nasa.gov) wrote:
>: What is a ferite bead? The one talked about below.

In article <C0GFvJ.2nH@srgenprp.sr.hp.com> rexm@sad.hp.com (Rex Musgrave)
writes:
>A ferrite bead is a toroid (doughnut) made of this iron based
>material. What the writer was talking about was to run the
>control wire through the center of the toroid, wrap it back
>around and through the center once again (one turn).

Mr. Musgrave explanation was correct except on one point.  The convention
when winding on inductors on a toroid is that the number of turns is the
number of times the wire passes through the center of the toroid.  (See,
for example, the ARRL Handbook, pg. 24-8 in the 1990 edition.)  Thus,
Mr. Musgrave describes a two-turn inductor, not a one-turn one.

The term ferrite bead, in my experience, usually refers specifically to
toroids intended for single turn inductors.  They are slid onto wires or
component leads or wires like beads on a necklace.  Usually, the center
hole is small, so there is only room for the wire to pass through once.

I get mine at hamfests or at Universal Amateur Radio.  My catalogs aren't
handy right now, but I'm sure that many mail order electronics houses
sell them.  One manufacturer (I think the name is Amidon) puts out an
excellent little brochure describing the various types of ferrite material,
the frequency ranges for each, and the color coding used to label them.

Another poster asked about the sizes available.  I've seen toroid cores
up to 8-10" in diameter.  These were intended for custom wound power
transformers, or for chokes for large cables such as thick coax.  Except
for prowling hamfests, I don't know a source for the large ones off the
top of my head.

The only thing Radio Shack carries are the snap together cores intended
for appliance-type power cords.  These are sometimes effective at
suppressing the RFI generated by lamp dimmers or heating pads.

-- 
Steve Brown, N8HFI              sbbrown@magnus.acs.ohio-state.edu
Chief Engineer, The Ohio State University Radio Observatory ("Big Ear")