On Sun, 11 Jan 2009 21:01:39 -0500, Paul Christensen wrote:
>Anyone know a source of small toroid donut cores in #31 material?
>Do they even exist?
Of course. Fair-Rite INVENTED the #31 mix about five years ago.
Since then, they have expanded and re-shaped their product line to
build nearly HF suppression components in nearly all common form
factors using #31 material. The link below is to their on-line
catalog. I don't know of any other mfrs who have duplicated the #31
mix yet.
http://www.fair-rite.com/cgibin/catalog.pgm#select:where4
Fair-Rite is THE mfr of the vast majority of ferrite parts sold to
hams. Vendors like Amidon, Palomar, the Wireman, and DX Engineering
buy these parts, create new part numbers for them, and resell them,
mostly at obscene markups (4X-5X is typical). Not only that,
they're selling obsolete parts -- mixes that are relatively poor
choices for HF suppression.
It is EASY to do business with Fair-Rite and their distributors.
Appendix One of my RFI tutorial lists a select handful of ferrite
parts that are quite useful to solve HF noise and RFI issues. It
also lists a half dozen very good industrial vendors who sell these
products in quantity at very good prices.
Anyone who organizes a group purchase in the 1,000-lot range can
buy #31 2.4-inch o.d. toroids for about $4, tax and shipping
included. The 1-inch i.d. "biggest clamp-on" sells for about $12 in
lots of 250 or so, and is electrically equivalent to three of the
toroids. When I lived in Chicago I helped organize a group purchase
that included a bunch of the SMC guys and the North Shore Radio
Club. We also had participation from the MPLS area and downstate
IL. That appendix includes a worksheet to help you decide how many
of what parts to order.
A year ago, we did a very large group purchase for the Northern CA
Contest Club (SF Bay area). This past summer I helped ND2T fix RFI
in his neighbor's A/V rig. Tom transmitted on each band while I sat
with the neighbor and figured out the coupling mechanisms involved.
Tom pulled a half dozen big clamp-ons out of his stash, we threw
them on the loudspeaker cables, and the RFI went away. Tom was
prepared, so it was easy. I had already prepared the neighbor for
paying them them, but Tom decided to make a gift of the ferrites to
his neighbor.
The tutorial is http://audiosystemsgroup.com/RFI-Ham.pdf
The Chicago group purchase was about 4 years ago. I wouldn't be
surprised if you could do another one by now. I'd start by
contacting W9DXCC, SMC, the North Shore club, and the contest club
in MPLS.
73,
Jim Brown K9YC
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