[time-nuts] Distribution amps and slew rate

Charles P. Steinmetz charles_steinmetz at lavabit.com
Sat Nov 3 19:39:38 EDT 2012

david wrote:

>Given that slew rate is so critical, why do we distribute sine waves 
>and perform the zero-crossing detection at every target instrument?

Magnus made some good points in response to your question. To 
elaborate a bit: it is much easier to provide a friendly transmission 
environment for a sine wave (single frequency), and sine waves are 
less sensitive to imperfections in the transmission environment 
(impedance discontinuities and mismatches, noise ingress, 
etc.).  Reflections in the transmission environment will put funny 
steps in what started life as clean square waves or pulses, and 
differential phase shifts will also mis-shape square waves or 
pulses.  This can even be a problem with sine waves -- see, for 
example, the NIST paper on the timing effects of distortion in sine 
wave sources for an example of the sensitivity of sine wave systems 
to harmonics (Walls and Ascarrunz, The Effect of Harmonic Distortion 
on Phase Errors in Frequency Distribution and Synthesis) -- but it is 
much worse with square waves or pulses.

Sine wave systems are also much less prone to radiating 
noise.  Anyone who operates one or more frequency standards as well 
as sensitive RF receivers can testify that sine waves are much less 
of a hassle.

Best regards,


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