On Tue, 7 Feb 2006 08:39:55 -0800, N7HIY wrote:
>few of the ferrite materials that exhibit high HF attenuation
>are usable in spit cores.
I've seen no reason to believe that is the case. They just aren't in the
catalog yet, for the reasons noted below.
>measure them anyway you like, sig. generator and spectrum analyzer, network
>analyzer, impedance bridge, vector impedance analyzer; none of the spit
>cores exhibit cost effective usable HF attenuation below 20 MHz. except type
>31 from Fair-Rite which is difficult to buy on the street.
#31 is VERY easy to buy from distribution if you don't limit yourself to the
few resellers who advertise in the ham marketplace. All you have to do order
from a Fair-Rite distributor -- see their website for a list. Ham
distributors don't sell them because they don't know about them (other than
DX Engineering, who has W8JI advising them). I've had good service from
Kreiger (in Virginia), and the west coast guys seem to like Lodestar.
#31 is a new material -- 2.4" O.D. toroid is a brand new part, so that makes
it more difficult to order. The ones we measured (about 18 months ago) were
early production samples. But we have since ordered and received 2,000 pieces
for several ham clubs as a group purchase. #31 is also less well known
because some RFI specs apply from 30 MHz up, and #31 acts like #43 at VHF.
It's at HF where its advantages show up.
For the research that resulted in the app note (and an AES paper), we tested
two large clamp-ons, and bought about 100 pieces of the larger one. It works
VERY well, both with multi-turn coils around cables where it's hard to take
off the connector, and around large conductors. That data is also in the app
note.
Jim Brown K9YC
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