On 3/24/2012 3:24 PM, Carl wrote:
> I would not recommend toroids above 40M and even there its iffy at high
> power. And of course use one per band.
Yes. I don't know anything about powdered iron materials, but all
ferrites get increasingly lossy with increasing frequency. A few
ferrite mixes are designed to handle high power, and are pretty low loss
at low to medium frequencies, but each of them has a high frequency
limit, beyond which their loss has increased to the point that they are
not very useful. For example, Fair-Rite #61 starts getting lossy above
about 10 MHz, while their #67 starts above 20-30 MHz. In general,
losses will couple from the core to the wires, and will show up in the
equivalent circuit as resistance.
Another issue is voltage breakdown -- ferrites are semi-conductors, and
each mix is different there too. Some are pretty good insulators, others
are fairly conductive. It's worth studying the Fair-Rite catalog, which
is really excellent. Fair-Rite data sheets include data for resistivity,
permeability and permittivity. If you have a solid EE background, it's
also worth calling Fair-Rite's technical support people. But study their
catalog and applications notes first so that you know what questions to
ask and can understand the answers.
73, Jim K9YC
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