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I have a Rigol DS1074Z and can't figure out how to lower the time the scope spends pre-sampling to open up more memory for the actual data I want to see.

Here is a nice image that will hopefully explain better:
Triggering and times

And here is what it looks like when I am trying to store beginning of USB communication:
50% waste

Unfortunately almost 50% of the 12 million data points are wasted. I would like to move the TriggerPoint in the first image closer to the beginning. In other words, I really only need to see what happens after the trigger triggers (any maybe a little bit before)

Is there a setting I missed? Can this be achieved?

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Yes, what you want can absolutely be achieved.

Before you capture a waveform use the horizontal position adjustment knob to change the position of the orange cursor at the top of the screen.

This first image show a capture from my scope with the horizontal position set to the center of the screen. The second image shows the same signal (but a new capture) with the trigger set close to the left side of the screen. You can see that in the second image I've captured much more of the signal.

Waveform capture with trigger in the center

Waveform capture with trigger near the left side

Annotated image of Rigol DS1104Z

I'm not familiar with your scope, but I think I've marked the correct knob. Also, there may be a setting you can change that will set the default horizontal trigger point to the left side of the screen.

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  • \$\begingroup\$ The scope I have is hardware identical to the image you posted :) But the issue is somewhat different. Yes I can move around the stored waveform left and right after I acquire it, BUT the scope acquires equal amount of time before and after the trigger event. In my case, I only care about what happens after the trigger event. So even though the scope stores 24 million data points, only 12 million (the 12M after the trigger) is useful to me. The issue is best shown on single acquisition as I tried to show in the second image. \$\endgroup\$
    – nana
    Jun 27, 2014 at 6:05
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For the rigol DS1000z series, the only way I have been able to do it is by using the "window" trigger type.

Push "menu" under trigger level adjustment knob. Then select window as the trigger type. Select time in the position box. The increase the time to match with half the number of points you have.

Example, if your sample rate is 350Ms/s with 3M sample points. ((350e6)^-1 * (3e6))/2 = .006 seconds in the time box.

Now your waveform take up the entire 3M points.

Unfortunately this doesn't adjust the trigger position like I would normally do in other scopes I've used, but achieves the same thing.

Now your FFTs will have more signal if you are triggering.

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In addition to @A.Mac answer, it's worth adding more details on Rigol behavior. You do need to scroll the view before capturing the signal, not after. The window position is defined relative to the trigger, and the trigger is assumed to be at the zero position always.

Apparently Rigol would center-aligh the sample buffer to match the window position. The way it is aligned doesn't really matter as long as the final position of the sample buffer will be such that the trigger would split that buffer in desired proportion. Note that the buffer position is readjusted only after the next successful capture, that's why you have to scroll the window while oscilloscope is sampling something (idk, put it in auto mode maybe).

Some pics. The first one shows the default case, when window position matches the trigger position.

enter image description hereSee the tiny orange triangle that is always in center, and the marker with letter T. They coincide in first picture.

Now scroll the window to the far right from the trigger.

enter image description here

You still see the darker portion of the history that matches the window within the whole buffer that is drawn in light grey. As you can see the window is centered within the buffer, or rather buffer is centered around the window. The split can look like it's 50/50, but note where the trigger marker is. It's far on the left. The buffer is located entirely after the trigger, so you have the whole buffer dedicated to the signal captured after the trigger.

After the signal is captured and sampling is stopped (single capture mode?) you can scroll to the left, or simply push the position knob to jump directly to trigger position. enter image description here

See this last pic, only few samples are recorded before the trigger, simply because I didn't position the window precisely.

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