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Guest

Thu Dec 20, 2018 7:45 am   



You may have seen me rail against how the schools teach that inversion is the same thing as 180 degrees out. Out of phase, by definition or etymology or whatever the fuck at least strongly implies that THIS signal is THAT signal but has gone though something that has delayed it by ½ its period.

Now, these two waveforms, say applied to a CRO (and ALWAYS own a CRO as long as you shall live) and syncing, they look the same as long as they are symmetrical. But we have two types of symmetrical.

Consider:

¯|_|¯|_|¯|_|¯|_|¯|_|¯|_|

/\/\/\/\/\/\/\/\/\/\/\/\

And:

/|/|/|/|/|/|/|/|/|/|/|/|/|

Or as my Wavtek will put out:

/|_/|_/|_/|_/|_/|_/|_/|_/|

With a dead time that is half the sawtooth wave.

Now, we should all know this, it is not that hard of a concept. But how is it expressed ?

If I was the word chooser of the world, a sawtooth wave would be called "Symmetrical in period" but NOT "Symmetrical in polarity".

What are the proper terms for that ?

Jeroen Belleman
Guest

Thu Dec 20, 2018 8:45 am   



jurb6006_at_gmail.com wrote:
Quote:
You may have seen me rail against how the schools teach that inversion is the same thing as 180 degrees out. Out of phase, by definition or etymology or whatever the fuck at least strongly implies that THIS signal is THAT signal but has gone though something that has delayed it by ½ its period.

Now, these two waveforms, say applied to a CRO (and ALWAYS own a CRO as long as you shall live) and syncing, they look the same as long as they are symmetrical. But we have two types of symmetrical.

Consider:

¯|_|¯|_|¯|_|¯|_|¯|_|¯|_|

/\/\/\/\/\/\/\/\/\/\/\/\

And:

/|/|/|/|/|/|/|/|/|/|/|/|/|

Or as my Wavtek will put out:

/|_/|_/|_/|_/|_/|_/|_/|_/|

With a dead time that is half the sawtooth wave.

Now, we should all know this, it is not that hard of a concept. But how is it expressed ?

If I was the word chooser of the world, a sawtooth wave would be called "Symmetrical in period" but NOT "Symmetrical in polarity".

What are the proper terms for that ?


Inversion symmetry and translation symmetry?

Jeroen Belleman

Look165
Guest

Thu Dec 20, 2018 10:45 am   



I would say an offset sawtooth.
Or a sawtooth with DC component.

The definition of 180° is not inversion, it is delayd by half a period.

Try the "inversion" with a asymetrical signal and see the result, though
it is periodic.

Exemple : MMMM.... delayed by half a period gives MMMM..... ; try to
invert it ! (something like WWWW).

On a scope, you would see the same trace since it is triggered even with
a dual-channel.

Sorry for my "French English" !


jurb6006_at_gmail.com a écrit :
Quote:
You may have seen me rail against how the schools teach that inversion is the same thing as 180 degrees out. Out of phase, by definition or etymology or whatever the fuck at least strongly implies that THIS signal is THAT signal but has gone though something that has delayed it by ½ its period.

Now, these two waveforms, say applied to a CRO (and ALWAYS own a CRO as long as you shall live) and syncing, they look the same as long as they are symmetrical. But we have two types of symmetrical.

Consider:

¯|_|¯|_|¯|_|¯|_|¯|_|¯|_|

/\/\/\/\/\/\/\/\/\/\/\/\

And:

/|/|/|/|/|/|/|/|/|/|/|/|/|

Or as my Wavtek will put out:

/|_/|_/|_/|_/|_/|_/|_/|_/|

With a dead time that is half the sawtooth wave.

Now, we should all know this, it is not that hard of a concept. But how is it expressed ?

If I was the word chooser of the world, a sawtooth wave would be called "Symmetrical in period" but NOT "Symmetrical in polarity".

What are the proper terms for that ?


John Larkin
Guest

Thu Dec 20, 2018 11:45 pm   



On Wed, 19 Dec 2018 21:46:29 -0800 (PST), jurb6006_at_gmail.com wrote:

Quote:
You may have seen me rail against how the schools teach that inversion is the same thing as 180 degrees out. Out of phase, by definition or etymology or whatever the fuck at least strongly implies that THIS signal is THAT signal but has gone though something that has delayed it by its period.

Now, these two waveforms, say applied to a CRO (and ALWAYS own a CRO as long as you shall live) and syncing, they look the same as long as they are symmetrical. But we have two types of symmetrical.

Consider:

|_||_||_||_||_||_|

/\/\/\/\/\/\/\/\/\/\/\/\

And:

/|/|/|/|/|/|/|/|/|/|/|/|/|

Or as my Wavtek will put out:

/|_/|_/|_/|_/|_/|_/|_/|_/|

With a dead time that is half the sawtooth wave.

Now, we should all know this, it is not that hard of a concept. But how is it expressed ?

If I was the word chooser of the world, a sawtooth wave would be called "Symmetrical in period" but NOT "Symmetrical in polarity".

What are the proper terms for that ?


We use "symmetric" to mean flippable on the vertical axis, amplitude.

The concept of "time reversal" is pretty rarely discussed, so we say
that when we mean it.

CRO? Those funny old things with electron guns and deflection plates?
Haven't use one in a decade or two.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Jasen Betts
Guest

Thu Dec 20, 2018 11:45 pm   



On 2018-12-20, jurb6006_at_gmail.com <jurb6006_at_gmail.com> wrote:
Quote:
You may have seen me rail against how the schools teach that inversion is the same thing as 180 degrees out. Out of phase, by definition or etymology or whatever the fuck at least strongly implies that THIS signal is THAT signal but has gone though something that has delayed it by ½ its period.

Now, these two waveforms, say applied to a CRO (and ALWAYS own a CRO as long as you shall live) and syncing, they look the same as long as they are symmetrical. But we have two types of symmetrical.

Consider:

¯|_|¯|_|¯|_|¯|_|¯|_|¯|_|

/\/\/\/\/\/\/\/\/\/\/\/\

And:

/|/|/|/|/|/|/|/|/|/|/|/|/|

Or as my Wavtek will put out:

/|_/|_/|_/|_/|_/|_/|_/|_/|

With a dead time that is half the sawtooth wave.

Now, we should all know this, it is not that hard of a concept. But how is it expressed ?


Periodic waves all have translational symmetry in the time dimension

The first two have glide reflection symmetry, and also mirror
symmetry (at any peak or trough) and rotatinal symmetery (about any zero-crossing)


the last has, only translational symmetrty in the time dimension
the second last has in addition the rotational symmetry


this (square wave through low-pass filter) has glide reflection (on time and voltage)
but not time refelction. or rotation

_ _ _ _ _ _ _ _ _
/ | / | / | / | / | / | / | / | / |
| \_| \_| \_| \_| \_| \_| \_| \_| \


This (uneven square wave) has time reflectional symmetry on time but
not glide reflection or rotatiom
_ _ _ _ _ _ _ _ _
__| |___| |___| |___| |___| |___| |___| |___| |___| |__


--
When I tried casting out nines I made a hash of it.

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