# frequency & amplitude { confused }

• posted

Hi...,

well, I'll jump straight into the theory.

Wave equation is a ii order hyperbolic PDE

by solving it with the principles of superposition( Fourier concepts )

we can take the solution of the wave equation as

y =3D A cos( 2 * pi * f + phi )

I think this is the back bone of the most of the electronic stuff.

From a given crystal we can produce only frequency, but not amplitude.

my doubts was,

(1) how amplitude was produced depending our requirements ? what is logic behind that ?

cheers nimo ________

It=92s a good thing we have gravity, or else when birds died they=92d just stay right up there.Hunters would be all confused.

StevenWright, comedian.

• posted

Tolerably complete mathematical descriptions of real electronics include non-linear terms.

Crystal oscillators mostly rely on (non-linear) output stage clipping to limit the amplitude; the Q of the crystal is high enough that harmonics that this produces are too low to be easily measured.

The logic reduces to the observation that we build it, see if it works, and if it works we analyse it to make sure that we understand the way it works, so that we can be reasonably sure that it will keep on working.

Sometimes we build a nathematical model and see if that works, but no model is perfect, so we've still got to build the real thing at some point or other, just to check whether we've made the right simplifications.

-- Bill Sloman, Nijmegen

• posted

thanks bill for the clarifications;

but my doubt was..,

How amplitude(of a wave) was produced from an Oscillator, where as it is only capable of producing Frequency ( for provided inputs )

take for example Quartz crystal, it can produce the wave which we can have control over its frequency.., but how it's amplitude is handled ?

got my doubt ? ________ so long nimo

I was amazed that cats had holes cut into their fur precisely in those places where they had eyes.=92

Georg Christoph Lichtenberg (1742=961799)

• posted

The linear-model equations that yield the frequency do NOT INCLUDE the amplifier large-signal model. All amplifiers (tubes, transistors, op amps, even sparkgaps near breakdown) have operating curves that (at one point or the other) have a power gain. The majority of oscillator circuits do not bias the amplifiers to remain in that power-gain region, so the amplifier will clip/distort/turn off for large parts of the cycle.

The exception is a class of not-very-power-efficient oscillators that give low-distortion sinewaves, including phase shift oscillators and Wien bridge oscillators. Dynamic gain-control techniques are employed to stabilize these amplifiers (notably, the resistance temperature dependence of a lamp filament acted to limit the gain in HP200 series audio oscillators). A 10 kHz oscillator that employs a gain-of-3 amplifier will be 10% in error on its amplitude after one second if the gain is 3.000 02 ; this accuracy of gain is too high to achieve with fixed components, there HAS to be a robotic feedback to keep it going.

• posted

If the output of the oscillator has an amplitude of zero, it has no usable output signal.

The equations you mentioned in your first post may not indicate any output amplitude, but for any oscillator to be useful, it must produce a signal of some amplitude.

I find it more amazing that the cat's eyes are located so that they line up with the holes in the fur.

```--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca  ```
• posted

Correct;

voila; what my point is.,

How can we produce required "Amplitude" for our needs ?

where as different crystals can only produce frequencies., that means

we can have control over crystal's frequency, but not amplitude., that means

=3D> how that mighty Amplitude "modulation" is done ?

clever., keep it up

• posted

The design of the oscillator circuit will determine its output amplitude. Then we amplify (or attenuate) the output of the oscillator as needed.

```--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca  ```

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