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Old 18th Mar 2017, 12:16 pm   #21
kalee20
Dekatron
 
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
Default Re: Permeability Tuning

If the loss resistance is independent of frequency - ie mostly the DC resistance of the coil, then:

Q = (1/R)[√(L/C)]

We also have:

Q = fres / BW (bandwidth)

and fres = 1/[2π√(LC)].

Putting these together, we have:

BW = R/(2πL)

Thus for constant bandwidth, you should vary C because bandwidth is independent of C!

In practice, as Al Skywave says, DC resistance is not the whole story, there is some parallel loss resistance as well as frequency-dependent series resistance. But this analysis is revealing, nonetheless!
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