Re: Lissajou patterns



cubik@xxxxxxxxx wrote:
> Hi!
>
> I am having problems with displaying Lissajou patterns (for educational
> purpose) with a Tektronix 2246 and I need some help.
> I have one and only one function generator set to display sinusoidal
> signal. I put a T BNC connector on the output plug of the generator on
> plug to 50 ohms BNC to it and I have connected the 2 ends to the scope
> on CH1 and Ch2.
> I have inverted the CH2 to have the exact same signal and frequency
> inverted. I have changed the mode to XY and I am getting 2 diagonals
> lines (like this <).
> >From there I cannot get any Lissajou figures. I have tried to change to
> different mode, different type of current and different everything but
> nothing works.
> I would really appreciate a little help from confirmed technician which
> I am obviously not...
> Thank you.

Apparently your output is exactly right. The whole point of Lissajous
figures (cue "The Outer Limits" music -- "Do not adjust your screen.
We control the horizontal. We control the vertical") is comparing
frequencies and phases. If they're both identical, you aren't going to
get any more than what you have.

You might want to try getting a second function generator, or cobbling
up a PLL circuit or something else to get two different frequencies to
compare.

Actually, Lissajous figures are still vitally important in electronics.
If I have to read a manual or data *** or do something important on
their problem that doesn't require wrench twiddling, and they want some
wrench twiddling on their problem RIGHT NOW, I have been known to set
up a Lissajous figure on my bench scope with one frequency drifting
slightly to cause slow but constant motion on the display. I then put
the scope on my bench next to the protoboard, with a large sign stating
"CAUTION -- TEST IN PROGRESS!" That has a tendency to keep
non-technical people out of my hair so I can think. For some reason,
they stare at the display for twenty seconds or so, then walk away with
either a blank or frustrated glance. I think there's something about,
say, a slowly drifting 4:3 or 3:2 display that causes great inner
confusion in non-technical persons. ;-)

Good luck with the homework. Try googling with a different spelling --
there are a lot of results for "Lissajous figure setup" (no quotes).

Chris

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