[AMPS] Chokes

[Tom Rauch]

Hi Marv,

> >Q of that material, or inductors wound on that material, is ten at 10
> >MHz.
> 
>   My Fair-Rite catalog (13th ed. p. 10) shows about a Q of 85 at 10 MHz,
> do you have a different source?

I don't have that catalog, but the ratio of parallel resistance to 
reactance in the charts I have shows 61 material has a ratio of ten 
at ten MHz. When I look up the specs on 61 shield beads, they 
follow that exactly. 

>    Sounds reasonable but, the question is how much energy is actually
> being imparted to the core?

You can bet a whole lot of energy is if the core is inside the 
winding. Flux will concentrate in the core.
 
> >>   I don't have any formulas for flux density in rods... do you have a
> >> reference?
> >
> >Flux density is not the problem, since saturation isn't the issue 
> >unless the duty cycle is so short heating is not a limitation. 
> 
>    I beg to differ, since the flux density mulitplied by the loss factor
> is the power loss... or heating.

That's certainly a VERY long way around the park to get to the 
gate!!!! We know Rp, we can use Ep to calculate dissipation in one 
simple step in our heads without the aid of a calculator, and it will 
include all losses.

> >I think most chokes in this application should have a Q in the 
> >hundreds, not single digits. That would require mounting the 61 
> >ferrite off to one side on the outside of the choke, and a few winding
> >diameters away. Maybe on the cabinet wall.
> 
>    It wouldn't do much over there... for the inductance.

That's right. And that also means it won't de-Q the choke and lower 
Rp to the point where the choke glows in the dark.

  
73, Tom W8JI
w8ji@contesting.com

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