It's a ferrite core with one or more holes through it with wires
threaded through them.  It has lower distributed capacitance than
a toroid, so sometimes does better than a toroid at HF and up.
You can buy them in different materials for different frequency
ranges.  If you have a choice, pick the type that has highest=20
impedance near the interfering frequency.  If you don't have a=20
choice, just use whetever you can get your hands on, it'll probably
help.

You can put them in series with the signal and return lines near=20
the connector in the box with your first stage of amplification.
I also put them on any power supply lines coming into an amplifier.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=3DM8694-ND

Jack


-----Original Message-----
From: psn-l-request@.............. [mailto:psn-l-request@............... On=
 Behalf Of Thomas Dick
Sent: Saturday, February 20, 2010 3:10 PM
To: psn-l@..............
Subject: Re: Ham radio interference

Jack Ivey wrote:
> It may be useful to add ferrite bead inductors in series with your signal=
=20
> lines close to the amplifier.  They will have no effect on the desired
> signal.  The 6-hole beads seem to work well.
>  =20
Thanks Jack for your reply. But what is a ferrite bead? I do use=20
toroids? Maybe I'm not current enough>
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