In RF design there are lots of "cookbook" formulas that we have pretty well ingrained in our craniums. However, there are a lot of cases where you have to do "inside out" calculations that involve some algebraic twiddling. These formulas aren't normally found in tables of such things. For instance, if you have a resonant circuit with a known frequency and a known value of inductance, what value of capacitance does one need?

A brown star for the first one who comes up with the formula which gives C in terms of L and f.

Eric

 

In RF design there are lots of "cookbook" formulas that we have pretty well ingrained in our craniums. However, there are a lot of cases where you have to do "inside out" calculations that involve some algebraic twiddling. These formulas aren't normally found in tables of such things. For instance, if you have a resonant circuit with a known frequency and a known value of inductance, what value of capacitance does one need?

A brown star for the first one who comes up with the formula which gives C in terms of L and f.

Eric

P.S. : As always, show your work.

 

C=1/(4.π^2.f^2.L)
Although I don't do radio, I use it quite often to make a low-pass filter using the leakage inductance of a transformer, with a capacitor across the secondary.

But can you remember the NTC thermistor equation? (just the basic one, not the full Hart-Steinhart)

 

C=1/(4.π^2.f^2.L)
Although I don't do radio, I use it quite often to make a low-pass filter using the leakage inductance of a transformer, with a capacitor across the secondary.

But can you remember the NTC thermistor equation? (just the basic one, not the full Hart-Steinhart)

Very good. You get the brown star.
As far as themistors are concerned, we used R(T) = R(T0)e−β(1/T0−1/T). However, BETA is a hugely complex formula which I've long forgotten.

 

I keep this around to save time:

 

ω^2 = 1/LC

 

ω^2 = 1/LC

Almost. But this is

ω^2 = 1/LC = (1/L)C = C/L

You need

ω^2 = 1/(LC)

The parens are not superfluous.