[time-nuts] beats was Re: If there a FAQ
jimlux
jimlux at earthlink.net
Mon Nov 29 14:51:46 UTC 2010
jmfranke wrote:
> Accurate Zero Beating, another perspective.
><snip>
The waxing and waning rate is determined solely by the
> beat between the WWV transmission and the unknown source. It is now
> easy to reliably adjust the unknown, or its harmonic, to within a
> fraction of a Hertz of the WWV transmission.
>
if one has a voltmeter (or total power detector, like your ear), hearing
low frequency beats at sub-1Hz is easy.. (anyone who has tuned an
instrument by ear, or sat in a plane with poorly synchronized engines
will know this)
consider the sum of two sinusoids cos(1.01*2pi* t) + cos (2*pi*t)...
when the two are in phase (say, at t=0), the amplitude is 2 (RMS =
1.414).. but, when they are just out of phase (say, at t = 50), the
amplitude of the sum is zero, and then, at around t= 100, they're in
phase again and the amplitude is back to 2.
This is different than the "saturated mixer" sort of thing, where you
get an explicit sum and difference.
More like spring and neap tides.
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