On Tue, 01 Feb 2005 10:07:04 -0500, Joe Giacobello wrote:
>Just curious, because I just bought a bag of inexpensive ferrites on
>Ebay, and they didn't start showing a resistive component until about 7
>MHz. Name brand ferrites specified for amateur applications (e.g.,
>Fair-Rite) show a resistive component at 2 MHz and below and have a
>higher reactive component until about 11.5 MHz, where the cheap ones
>become more reactive. However, their resistive component was still
>substantially below the Fair-Rite.
it is not a matter of "cheap" or "name brand," but rather the purpose for
which the particular ferrite bead or sleeve is designed. Go to www.fair-
rite.com, download and study their pdf catalog. It is a WEALTH of
information about ferrites of all sorts. The ferrites you got are obviously
a "mix" and shape designed for suppression use at VHF and/or UHF.
To answer the other question, YES, YES, YES -- ferrites used for
suppression should be as resistive as possible and have as little reactance
as possible in the frequency range where you want suppression, and for
precisely the reason Tom talked about -- you don't want the reactance to
partially or completely tune out the reactance of the wire you're putting
it on, or, if it does, you want there to be lots of R in the series
equivalent circuit.
Jim Brown K9YC
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|