On 6/30/2021 5:34 AM, Jim wrote:
DO NOT use toriods. I speek from experiance. Had a reaction when on 10
meters with my 8877 amplifier. The 160 meter toriod coils would start
smoking when on 10 meters. I was using a shorting switch.
"Toroid" is a shape in which hundreds of very different materials are
manufactured. I know nothing about powdered iron toroids (although they
are very successfully used in the 5B4AGN-designed bandpass filter kits I
built years ago), but I know a LOT about ferrite toroids.
The Fair-Rite catalog is a treasure trove for learning about ferrite
materials. The company has developed several dozen different chemical
mixes for very specific purposes, and there are mixes that can handle a
lot of power in specific frequency ranges. These mixes have been
assigned numbers. In general, these materials have low loss at low
frequencies, high loss at higher frequencies.
Over the years, a few select companies have published technical data and
applications notes so detailed and filled with information that you can
learn as much from them as from colleges and technical schools. Those
published by RCA (tubes), National Semiconductor, Electro-Voice
(loudspeakers) are examples. The Fair-Rite catalog is deservedly within
this group.
The catalog is here.
http://www.fair-rite.com/files1/Fair-Rite_Catalog_17th_Edition.pdf
Beginning on page 10, start by reading the brief description at the top
of the page for each material, then studying the graph of "Complex
Permeability vs. Frequency." On this graph, mu' is the purely inductive
permeability of the material, mu'' is the resistive component, where R
and X are in series.
For example, in the first entry, #68, permeability is fairly low (about
15), but loss is also quite low up to about 100 MHz, where it begins to
rise rapidly. The next entry, #67, has higher permeability (about 25)
and comparably low loss up to about 30 MHz. N6RK, a very smart engineer
who retired from HP some years ago, has used #67 toroids for high power
transformers.
Ferrite materials are useful as common mode chokes for RFI suppression
in frequency ranges where they are very lossy. #61 is useful as an
inductor core (including transformers) at HF, but starts getting lossy
around 10 MHz (where mu'' starts rising), and is sufficiently lossy at
UHF that it's useful for suppression.
73, Jim K9YC
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