[time-nuts] Phase modulation detection/NIST plan

David I. Emery die at dieconsulting.com
Fri Jul 13 23:49:15 UTC 2012


On Wed, Jul 11, 2012 at 03:48:52PM -0400, paul swed wrote:
>  David
> Read your comments and have been traveling. So finally a chance to email.
> 
> I read the document also and walked away with what I shared.
> In your reading would you believe the following.
> Its an absolute phase and that when it switches to 0 there is 1 transition
> at the beginning of the second to 180 degrees staying that way to the next
> bit or flipping again to 0 degrees if its a 1 at the 1 sec tic???

	What I mean by absolute phase is that a 1 is always 180 degrees
and a zero always 0 degrees.  In your example this would imply that the
two ones in a row would result in two seconds of 180 degree phase
without a flip after the first 1.

	The document is confusing, but the best I can do with its
language is to conclude they are talking about absolute phase.  Normally
when one talks about baseband waveforms one is referring to absolute I
and Q components relative to an unchanging carrier phase, not relative I
and Q with respect to the last bit phase.   So I take their language to
mean a zero is 0 degrees and a 1 180 degrees relative to an unchanging
carrier.

	Differential encoding is the opposite, a 1 is always the
opposite phase from the last bit, a zero always the same phase as the
last bit (or sometimes  the inverse where a zero is the transition and a
one is not).


> Is there a way to sense from the document that there is a bias towards 0
> lets say.

	Differential encoding tends to have little "DC" component or
bias toward either one or zero or one phase or the other, absolute
encoding does if the data it encodes does.

--
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."




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