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The Tektronix TDS430A is a 400 MHz 100 MS/s oscilloscope. I know other ocsilloscopes which could be toggled between analog mode and digital mode, so that these numbers would make sense. However, it seems the TDS430A is digital only. How could they possibly measure 400 MHz with only 100 MS/s?

Tektronix TDS430A Label

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    \$\begingroup\$ We had a bunch from Agilent/Keysight in my lab with 25 GHz bandwidth but only ~40 kSa/s. The newer models have boosted that to ~80 GHz bandwidth with ~1 MSa/s. \$\endgroup\$
    – The Photon
    Commented Dec 23, 2020 at 18:44

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They're stating that the bandwidth of the analog front end is 400MHz. For a periodic signal then you could fill in the waveform by sampling successive sweeps.

So you could for example see a 400Mhz sine wave on the scope (though 3dB down) with this technique.

For a single shot or non-periodic signal you would be limited by the sample rate.

From the manual:

enter image description here

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  • \$\begingroup\$ Ah, like the LeCroy RIS (Random Interleaved Sampling) mode? \$\endgroup\$
    – Thomas Weller
    Commented Dec 23, 2020 at 18:43
  • \$\begingroup\$ @ThomasWeller Yes, exactly. \$\endgroup\$
    – John D
    Commented Dec 23, 2020 at 18:44
  • \$\begingroup\$ Do you happen to know what that function is called on the Tektronix? It certainly needs to be enabled somehow \$\endgroup\$
    – Thomas Weller
    Commented Dec 23, 2020 at 18:45
  • \$\begingroup\$ @ThomasWeller Updated my answer with the relevant section from the TDS430A manual. \$\endgroup\$
    – John D
    Commented Dec 23, 2020 at 18:55
  • \$\begingroup\$ I have used many models of Tek scopes and never recall having to enable this feature, it is automatically enabled at small time scales. If you have a signal that is periodic, but slightly different each time, you will get some weird ghosting. \$\endgroup\$
    – Mattman944
    Commented Dec 23, 2020 at 23:21

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