Re: Resonant Systems

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

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

dwp wrote:
> Random energy added to a resonant system (acoustic or electrical)
> tends to add to the resonant system.
Ed wrote:
> to me that implies you can provide an impulse at random times with
> respect to an individual cycle.  The excitation must be synchronous
> with the oscillation of the system
dwp wrote:
> However, random excitation of a resonant system (some systems
> aren't) will also demonstrate resonance. 

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.

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
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