Jim
We were speaking of using toroids for RF TANK CIRCUITS.
Not common mode chokes.
Thanks
73
Jim W7RY
On 6/30/2021 1:41 PM, Jim Brown wrote:
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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