Will Matney wrote:
> That;s what I thought too until the Guys at Palomar Engineers
> mentioned using 61.
>
> Below is from Amidon;
>
> Material 61 (µi = 125):
> Offers moderate temperature stability and high 'Q'
> for frequencies 0.2 MHz to 15. MHz.
> Useful for wideband transformers to 200 MHz
> and frequency attenuation above 200 MHz.
> Available in toroids, rods, bobbins and multi-aperture cores.
>
> Material 63 (µi = 40):
> For high 'Q' inductors in the 15 MHz to 25 MHz frequency range.
> Available in toroidal form only.
>
> Material 43 (µi = 850):
> High volume resistivity. For medium frequency inductors
> and wideband transformers up to 50 MHz.
> Optimum frequency attenuation from 40 MHz to 400 MHz.
> Available in toroidal cores, shield beads, multi-aperture cores
> and special shapes for RFI suppression.
>
>
> So 43 wouldn't be any good for 6 meters at all,
> they'd have to use looks to me like 61.
> However, if 61 saturates at 10-13 MHz, what do you use?
> Would you use a larger stack than normal to keep it
> from saturating or is 10-13 MHz it's maximum limit
> regardless of the literature?
> That's my problem, what to spec as I may have to leave out
> ferrite transformers all together from the app if
> I cant resolve this.
>
> One place I hear one thing, and one another.
> Seems like I have never seen a source for ferrite or iron powder
> yet on the net, or in literature that I can trust.
First of all, there is some confusion using the word "saturates".
Magnetic saturation involves a sharp drop in permeability as the
magnetic flux passes through some large positive or negative value.
It has almost nothing to do with frequency.
The two important aspects of any ferromagnetic material for high
frequency use are permeability versus frequency and loss versus
frequency and flux swing.
If a core is use for energy storage, for instance as the inductor in a
filter or tank, it stores that energy by accumulating flux. So
significant flux swing is implied, and all the loss mechanisms that
take place during a flux swing cycle. But if a core is used as a
transformer core that only couples energy from one turn to another,
then there may be very little flux involved (which goes up by the
volts*seconds of each half cycle, so higher frequencies imply lower
flux swing) permeability and conductivity (that provides a one turn
sneak load across the transformer), are about all that matter.
That is why they say that type 61 is usable for wide band transformers
(turns coupling applications) up to 200 MHz, where its permeability
goes to crap, but is usable for high Q (energy storage, since Q is the
energy stored divided by the energy lost, each cycle) only up to 15
MHz, because its loss per cycle for large flux swings goes to crap there.
So the first stem in defining an appropriate material is to put the
application in the turns coupling or energy storage category.
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