[SOLVED] Frequency Sweep / Sync Issue on HP 3325B Function Generator

[robertneville777]

My almighty Cheb2ords! I bow to thee and humbly implore thy gracious wisdom...

So I'm following Dave's YouTube tutorial on how to "Bode plot" on an oscilloscope using a function generator:



So if I understand this correctly:

The function generator sends out of the main output a frequency sweep in 1 second. It also sends out a 1 Hz square wave via the sync output, which is aligned with the main output sweep.

You then use Ch1 to view the frequency response, and Ch2 to trigger off the sync square wave.

So over a period of one second, (and if I set my triggers right) I should only see one period of the 1Hz square wave, and only one frequency sweep.

Now my problem: The function generator is not sending out a 1 Hz square wave even though the sweep time is 1 second. The square sync wave is "sweeping" along with the main output wave. I looked in the manual and it doesn't say anything about changing the frequency of the sync wave.



I've seen other function generators do this, so my question is, am I just not setting up the function generator correctly? Or is the function generator not capable? (It is an older HP).

HP3325B Operating Manual: http://exodus.poly.edu/~kurt/manuals/manuals/HP%20Agilent/HP%203325B%20Operating.pdf

[w2aew]

Use the Z-Blank output, or the X-drive output, on the back panel for your trigger. The SYNC output on that generator is a square wave aligned with the zero crossings of the main output, thus not what your want.

[macboy]

Use the Z-Blank output, or the X-drive output, on the back panel for your trigger. The SYNC output on that generator is a square wave aligned with the zero crossings of the main output, thus not what your want.

More explicitly, trigger on the negative slope of X-drive.
Or use X-Y mode with X drive as the X signal (this is the intended use of this signal). If you are using an analog scope with a Z blanking input, connect it also. The Z-blank output seems to be open-collector, so to use it as a trigger source may require an external pull up resistor. X-drive will work as-is, but make sure that your scope trigger input can accept 10V.

[w2aew]

Use the Z-Blank output, or the X-drive output, on the back panel for your trigger. The SYNC output on that generator is a square wave aligned with the zero crossings of the main output, thus not what your want.

More explicitly, trigger on the negative slope of X-drive.
Or use X-Y mode with X drive as the X signal (this is the intended use of this signal). If you are using an analog scope with a Z blanking input, connect it also. The Z-blank output seems to be open-collector, so to use it as a trigger source may require an external pull up resistor. X-drive will work as-is, but make sure that your scope trigger input can accept 10V.

It depends a little on the scope.  Most digital scopes default with the trigger position in the middle of the screen, so triggering on the middle of the rising slope of the X-drive signal would do fine.  If the trigger position is at the left edge, then triggering on the falling edge would be best.  And of course, using is as the X signal in XY mode is exactly how it was intended to be used...

[robertneville777]

Hi guys, just wanted to say thanks! Triggering off that x-drive output in the back of the function generator works great!

Also, w2aew, love your YouTube videos! Keep it up!

Do you guys do like other forums and change the title to something like: "[SOLVED] Bode Plotting Issue on Oscilloscope"? Or just leave it alone?

[w2aew]

Hi guys, just wanted to say thanks! Triggering off that x-drive output in the back of the function generator works great!

Also, w2aew, love your YouTube videos! Keep it up!

Do you guys do like other forums and change the title to something like: "[SOLVED] Bode Plotting Issue on Oscilloscope"? Or just leave it alone?

Thanks! I'm glad you enjoy my videos...

[EEVblog]

Do you guys do like other forums and change the title to something like: "[SOLVED] Bode Plotting Issue on Oscilloscope"? Or just leave it alone?

No rule for that, it's up to the original poster.