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From Oscilloscope to Wireshark: A UDP Story (2022)

mattkeeter.com

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Re: From Oscilloscope to Wireshark: A UDP Story (2022)

#11

Post by Junk_Collector »

KK7NIL wrote: post #3
Retr0id wrote: post #2

> I configured the oscilloscope to collect 100M samples at 1 TSPS Typo? I didn't think we had sample rates anywhere near that high!

A Keysight UXR can do one quarter of that, 256GS/s, but a Tektronix 6 series is limited to 25 GS/s iirc, so you're right.

If you are an absolute nutcase, you could characterize a set of line stretchers and a multiplexer on a high end VNA then offset the inputs of the 4 channels on that UXR with them, take a capture and finally rebuild a 1TSamp/s signal out of the 4 results.

You have to have the 240V model of the scope to run all four channels at full rate (110GHz) though.

Re: From Oscilloscope to Wireshark: A UDP Story (2022)

#12

Post by jacquesm »

Junk_Collector wrote: post #11
KK7NIL wrote: post #3

Earlier quoted context omitted.

A Keysight UXR can do one quarter of that, 256GS/s, but a Tektronix 6 series is limited to 25 GS/s iirc, so you're right.

If you are an absolute nutcase, you could characterize a set of line stretchers and a multiplexer on a high end VNA then offset the inputs of the 4 channels on that UXR with them, take a capture and finally rebuild a 1TSamp/s signal out of the 4 results. You have to have the 240V model of the scope to run all four channels at full rate (110GHz) though.

Take that Nyquist ;)

Re: From Oscilloscope to Wireshark: A UDP Story (2022)

#13

Post by cesaref »

Junk_Collector wrote: post #11
KK7NIL wrote: post #3

Earlier quoted context omitted.

A Keysight UXR can do one quarter of that, 256GS/s, but a Tektronix 6 series is limited to 25 GS/s iirc, so you're right.

If you are an absolute nutcase, you could characterize a set of line stretchers and a multiplexer on a high end VNA then offset the inputs of the 4 channels on that UXR with them, take a capture and finally rebuild a 1TSamp/s signal out of the 4 results. You have to have the 240V model of the scope to run all four channels at full rate (110GHz) though.

The older Tektronix TDS540 series did this, but at much lower rates as was common in those days though. Internally there are differential feeds from the very beautiful hybrid ceramic input boards to 4 DACs, with some clever switching so that a single input can be sampled by all 4 DACs with a suitable offset to create 4x the sample rate when running with all 4 inputs.

The calibration procedure on the scope fiddles with the time alignment to get the different DACs correctly offset so that the combined signal is correct.

The hybrid ceramic input boards in their metal cases are a thing of beauty, fragile (don't ask how I know), but beautiful.

Re: From Oscilloscope to Wireshark: A UDP Story (2022)

#14

Post by mkeeter »

Retr0id wrote: post #2

> I configured the oscilloscope to collect 100M samples at 1 TSPS Typo? I didn't think we had sample rates anywhere near that high!

Not a typo, but you’re correct about the sample rate - with those settings, the scope was doing interpolation between samples.

Re: From Oscilloscope to Wireshark: A UDP Story (2022)

#15

Post by nomel »

mkeeter wrote: post #14
Retr0id wrote: post #2

> I configured the oscilloscope to collect 100M samples at 1 TSPS Typo? I didn't think we had sample rates anywhere near that high!

Not a typo, but you’re correct about the sample rate - with those settings, the scope was doing interpolation between samples.

By definition, you can't interpolate a sample. A sample is a measured value.

What you can do, if and only if you have an exactly repeating signal triggering at the same point within a cycle, is change the delay between the trigger and sample, and repeat. In other words, sample at different times within the same signal (since it's exactly repeating), to build up samples in time, of that waveform, to whatever time resolution you want.

Of course, you're limited to any noise in the trigger, variation in the signal, etc.

This is how you can record light moving through your garage [1]!

[1] https://www.youtube.com/watch?v=o4TdHrMi6do

Re: From Oscilloscope to Wireshark: A UDP Story (2022)

#16

Post by jacquesm »

nomel wrote: post #15
mkeeter wrote: post #14

Earlier quoted context omitted.

Not a typo, but you’re correct about the sample rate - with those settings, the scope was doing interpolation between samples.

By definition, you can't interpolate a sample. A sample is a measured value. What you can do, if and only if you have an exactly repeating signal triggering at the same point within a cycle, is change the delay between the trigger and sample, and repeat. In other words, sample at different times within the same signal (since it's exactly repeating), to build up samples in time, of that waveform, to whatever time reso…

Not sure if mkeeter's comment has been ninja edited but it says between samples, it doesn't say it is interpolating to generate new samples.

Re: From Oscilloscope to Wireshark: A UDP Story (2022)

#17

Post by nomel »

jacquesm wrote: post #16
nomel wrote: post #15

Earlier quoted context omitted.

By definition, you can't interpolate a sample. A sample is a measured value. What you can do, if and only if you have an exactly repeating signal triggering at the same point within a cycle, is change the delay between the trigger and sample, and repeat. In other words, sample at different times within the same signal (since it's exactly repeating), to build up samples in time, of that waveform, to whatever time reso…

Not sure if mkeeter's comment has been ninja edited but it says between samples , it doesn't say it is interpolating to generate new samples.

I understand, but that's my point, it's not interpolated!

The number he's referring to is in units of samples per second. It's not doing interpolation between samples, to achieve a high samples per second, because that's not possible, which is my point. Interpolation results in an imagined value, but samples are measured values.

It would be correct to say that the values between samples are interpolated, but the subject of interpolation isn't applicable for anything mentioned in this comment chain.

Re: From Oscilloscope to Wireshark: A UDP Story (2022)

#18

Post by jacquesm »

nomel wrote: post #17
jacquesm wrote: post #16

Earlier quoted context omitted.

Not sure if mkeeter's comment has been ninja edited but it says between samples , it doesn't say it is interpolating to generate new samples.

I understand, but that's my point, it's not interpolated! The number he's referring to is in units of samples per second. It's not doing interpolation between samples, to achieve a high samples per second, because that's not possible, which is my point. Interpolation results in an imagined value, but samples are measured values. It would be correct to say that the values between samples are interpolated, but the subj…

Ah you are referring to the 'sps' bit. Ok, but I think the extra sentence is enough clarification of what they mean, even if they're wrong about what the device is doing.

The only time these are interpolating is when they are visualizing, there is no point (hah) in storing interpolated data, you can generate that whenever you want.

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