Re: Resonant Systems

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

> I have to side with dwp on this one.  A random forcing function
> applied to a resonant system (eg noise into a filter, pendulum
> blowing in the wind, road traffic rumbles into a gravity wave bar)
> will excite the resonance, to an amplitude commensurate with the
> amount of power available in the noise source across the bandwidth
> of the resonator.

	I was thinking of APPRECIABLE POWER.

> If in doubt, feed noise into a narrow band filter and look at the
> output of a narrow band filter on a scope.  Easy way to do this:
> scope probe the output stage of an IF amplifier in a receiver, or if
> you have a posh receiver, look and listen to the audio when a narrow
> CW filter is used.

> The phase and amplitude of the resulting resonance are band limited
> random functions, their rate of change limited by the bandwidth of
> the resonator, in other words they are each correlated over a
> timescale of around 1/BW.
> --
> Paul Nicholson

	Correct. Simple demo of that last point; feed a band-limited noise-like
voltage into a scope and set the trigger level near zero, the waveform
near the trigger point will be pretty much like a sinusoid, become more
noisy as you look out toward a time of 1/BW.

Ed