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shahzad-h

Tank ckt

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Anything that resonates with a high impedance makes a sine-wave. A sine-wave is very smooth without sharp edges. Sharp edges on a wave are caused by harmonic distortion because harmonics are added. A sine-wave doesn't have harmonics, just the fundamental frequency.

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At resonsance, the impedance approches infinity (this of course is impossible... there are always circuit paracitics).

From the WWW...

The solution to the circuit (which is a second order differential equation) is

i(t) = Ae ^+ jωt + Be ^− jωt

Considering the initial conditions, solve for A and B.

Because there is a complex exponential (thats the "j" part), the solution represents a sinusoidal alternating current.

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When calculating a tank, does the high impdeance differ if Xc=Xl=50 ohms from Xc=Xl=100 ohms?

When you connect the tank at the collector of a transistor, at DC the collector is at the supply voltage. When you apply the signal, does the peak hit the supply voltage, then go down from there with the size of the ouput signal? In other words, at what DC does the signal hover?

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When calculating a tank, does the high impdeance differ if Xc=Xl=50 ohms from Xc=Xl=100 ohms?

Hi Kevin,
Welcome back. ;D
The impedance of a tank circuit at resonance is determined by its Q. Usually it is the inductor's resistance that reduces the tank's Q. Therefore an inductor with a lower reactance would have a lower resistance then the tank would have a higher Q and a higher impedance, but with it the bandwidth is reduced.

When you connect the tank at the collector of a transistor, at DC the collector is at the supply voltage. When you apply the signal, does the peak hit the supply voltage, then go down from there with the size of the ouput signal? In other words, at what DC does the signal hover?

I haven't looked for many years, but when the DC collector voltage averages at the supply voltage because the resistance of the inductor is very low, then I think the signal voltage at the collector varies above and below the supply voltage.

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Thanks for leading me in the right direction concerning the first question. I had hoped a larger reactance might mean a higher impedance. Kind of disappointing. I don't like the second answer either. I was hoping it would just pull away from the supply voltage. Oh well.

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