[Amps] Guidelines.....toroids for tank ckts

[Jim Brown]

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