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Lecroy WavePro 950 sampling problems

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NPKNIIDAR:
Hello everyone, I want to ask experienced people for advice in solving my problem.

I have a WP950 1GHz 16Gs/s oscilloscope, the problem is that during the rise and fall of the signal, inadequate amplitude readings appear, the oscilloscope draws a straight line between them, and sharp "saws" are obtained that spoil the reading signal. That is, the oscilloscope is not showing the sample correctly.
For testing, I assembled a simple high-frequency oscillator at about ~600 MHz.

RIS helps a little, but it doesn't solve the problem, it only reduces it. It is not always possible to use RIS, more often I need a single shot signal. The "saw" is also visible in RIS.
I also want to note that the "saw" goes through if you turn on the second channel, the third, or all at once. From this I conclude that the sampling frequency is to blame. At 16Gs/s the signal is bad, and at 8Gs/s and 4Gs/s it's already more or less normal. I would like to use the full capabilities of the oscilloscope. I suggest you watch my video where I showed how it all looks. -



I also have a question about the fact that the oscilloscope sometimes thinks for a very long time. You turn it on, work, work, and sometimes it freezes, and sometimes you have to wait up to a minute. Automatic recalibration on reboot turns on by itself, although I turn it off. At the same time, the time is right. This means there are no real-time battery problems.
I'm even thinking of buying a new device, I really want a DDA-3000 or WavePro-7300A, but it's very difficult to find in Russia and neighboring countries for adequate money

Thanks for the help.
-Tim

DaJMasta:
On those WavePro scopes you have to turn on Sin(x)/x interpolation in the math menu, but if those datapoints are real and not an artifact of the sampling system, you may have a LOT of higher frequency noise on your signal (and if you're not filtering your 600MHz once it's generated, this is probably it).

If at the same sample rate you can visualize the test output and an unconnected DC signal and not see that trace noise, it is probably real.  You could try displaying just the measurement points instead of the lines and turning on a color graded persistence mode, which should give you a heatmap of the noise on the signal.

Also worth mentioning that measuring that fast means you need appropriate probes and probing.  Ideally, an active probe, but good passive probes may do the job, and definitely on the 50 ohm input termination (I believe the 1M inputs are only really rated for like 350MHz or so), and you want the minimum loop size between the probe tip and the grounding point.  If you're using alligator leads in any part of your probing, it is not going to be a good representation of any signal at 600MHz or above.

NPKNIIDAR:

--- Quote from: DaJMasta on September 22, 2021, 01:54:03 am ---Also worth mentioning that measuring that fast means you need appropriate probes and probing.  Ideally, an active probe, but good passive probes may do the job, and definitely on the 50 ohm input termination (I believe the 1M inputs are only really rated for like 350MHz or so), and you want the minimum loop size between the probe tip and the grounding point.  If you're using alligator leads in any part of your probing, it is not going to be a good representation of any signal at 600MHz or above.

--- End quote ---

I've experimented quite a bit with this and it's definitely a software bug or accurate calibration.
In my generator, there can be no such "noise" with a frequency of 16 GHz, it produces a pure sine of 588 MHz.
I also want to note that noise (interference) with a frequency of 16 GHz simply cannot pass through the probe, and even more so through the input path of the device.

In confirmation of my words, I connected the BNC-BNC cable and applied a calibration signal to the oscilloscope input. If the calibration signal is applied to other inputs, the situation is the same.

Kosmic:
I tried reproducing exactly the same setup with the calibrator output on my WavePro 960. I don't see any noise unfortunately.





This is most probably a hardware problem and not a bug in software.

Kosmic:

--- Quote from: NPKNIIDAR on September 21, 2021, 09:35:13 pm ---I also have a question about the fact that the oscilloscope sometimes thinks for a very long time. You turn it on, work, work, and sometimes it freezes, and sometimes you have to wait up to a minute. Automatic recalibration on reboot turns on by itself, although I turn it off. At the same time, the time is right. This means there are no real-time battery problems.

--- End quote ---

If time/div and num recorded samples are too high, the scope will slow down and take more time to capture everything. Normally when it's happening, I hit Stop and reconfigure the num of recorded samples to get acceptable responsiveness.

For autocal it will happen more often when the instrument is cold. After 10min it shouldn't happen that much.

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