Re: Difference between 1/2 wave and 1/4 wave resonance ? ? ?

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Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 05:52 PM 1/12/2004 -0700, you wrote:
>Original poster: "Mccauley, Daniel H" <daniel.h.mccauley-at-lmco-dot-com>
>
>Does anyone have how to calculate from an RLC circuit, both the 1/2 wave
>and 1/4 wave resonant frequency?
>
>A simple parallel resonant circuit Fres = 1/SQRT (L*C).  Now is this
>technically a 1/2 wave resonant frequency of
>this parallel resonant circuit?
>
>Any help appreciated in this confusing matter.
>
>Thanks
>Dan

One would usually think of waves in terms of a transmission line.

One can use a line terminated in anything other than it's characteristic 
impedance (i.e. a short or open) to look like a resonant circuit (in that 
the impedance presented at the terminals would look like that of a 
comparable RLC two terminal circuit).

A quarterwave line transforms the impedance at the far end according to: 
Zin*Zout = Z0*Z0 (Z0 is the characteristic impedance), so, a short at the 
far end looks like an open at the near end, and vice versa.

A halfwave line replicates the impedance at the far end at the near end 
(i.e. a short at the far end of a halfwave line looks like a short at the 
near end)

Maybe, one could compare a LC, at resonance, to an open circuited 1/4 
wavelength line?.. presents a very low impedance at the resonant frequency. 
As you move higher in frequency the line gets longer than 1/4 wavelength, 
and starts to look like an inductor. As you move lower in frequency, the 
line is shorter than 1/4 walength, and it looks like a capacitor.