PLL confusion

[peterken]

On Sun, 14 Nov 2004 22:03:52 GMT, "peterken" <peter273@hotmail.com
wrote:



"Active8" <reply2group@ndbbm.net> wrote in message
news:jfoso7x7flvq$.dlg@news.individual.net...
On Sat, 13 Nov 2004 09:54:34 GMT, Peter Lawton wrote:

I'm doubtful if 'phase' is the right word too. the phase difference
of
two
non - same frequencies increases over time and never repeats.


This is not true. A 5 and 10 Hz signal that start off in phase, will
be in phase after one cycle of the 5 Hz wave, for example.

wrong
It is indeed true the amplitude will be zero for both after one cycle of
the
5Hz signal, and the zero crossing will have the same direction
BUT
For a 5 and 10Hz signal that start off in phase the 5Hz signal will be
lagging a full 360deg (or 2*pi rad) after one cycle with respect to the
10Hz
signal.
It's PHASE to be considered, remember...


"jim" <road12fg@netscape.net> wrote in message
news:nfhkp0tapvonon5q3dlsfvk4rpsfhu73ut@4ax.com...
So is this correct....... That one can measure phase difference of two
different frequencies and amplitudes by picking any arbitrary
amplitude on the scope and just running a horizontal line through the
two waves and noting the intersection points? the complete phase curve
can then be obtained by raising or lowering the reference point ? But
what if one wave has twice the amplitude of the other? the horizontal
line will only intersect it and not the other. Does this imply that
only waves with equal amplitude can be measured for phase difference?
jim

One can take ANY reference point on two signals (eg 20deg after a positive
zero crossing of a single cycle or something like that), but easiest is to
take zero crossing of course.
When taking a reference for phase it's good practice to take something both
signals DO have, in this case zero crossing.
This way one can compare phases between any form of repetitive signals of
whatever amplitude since it's phase we are interested in...
As fo the "horizontal line" : adjust your scope (or other visualisation
means) so the displayed amplitude of both is equal, since that's not what we
are interested in measuring

 

[jim]

"jim" <road12fg@netscape.net> wrote in message
news:nfhkp0tapvonon5q3dlsfvk4rpsfhu73ut@4ax.com...
So is this correct....... That one can measure phase difference of two
different frequencies and amplitudes by picking any arbitrary
amplitude on the scope and just running a horizontal line through the
two waves and noting the intersection points? the complete phase curve
can then be obtained by raising or lowering the reference point ? But
what if one wave has twice the amplitude of the other? the horizontal
line will only intersect it and not the other. Does this imply that
only waves with equal amplitude can be measured for phase difference?
jim


One can take ANY reference point on two signals (eg 20deg after a positive
zero crossing of a single cycle or something like that), but easiest is to
take zero crossing of course.
When taking a reference for phase it's good practice to take something both
signals DO have, in this case zero crossing.
This way one can compare phases between any form of repetitive signals of
whatever amplitude since it's phase we are interested in...
As fo the "horizontal line" : adjust your scope (or other visualisation
means) so the displayed amplitude of both is equal, since that's not what we
are interested in measuring

Ok, I'm just about there,so you're saying that amplitude variation has

no effect on the phase relationships?