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| Has any one measured the -3 dB point for a SDS2104X HD w 100 to 200 MHz Update? |
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| mawyatt:
--- Quote from: Martin72 on February 25, 2024, 05:24:14 pm --- --- Quote ---Wonder why folks put so much emphasis on the pulse method to determine scope BW since the scope low pass filter charactistics are usually not known --- End quote --- I did this for years with the Bodnarpulser, for a trivial reason: I didn't have a source that could "go" that high to capture the bandwidths of my scopes. Maybe I wasn't the only one... ;) Now I have an R&S generator with which I can determine it as long as the scope is well below 1Ghz (R&S SML01). And even then you can't display such a frequency response for all scopes, with the siglents it works with the FFT peak function. Nevertheless, I still use the Pulser for the risetime determination, it is simply faster. For "more precise" then the method mentioned above with a sweep. --- End quote --- All one needs is a decent sinewave signal generator to measure scope BW, not necessarily accurate in amplitude just uniform across the frequency range of interest. It takes just two measurements, one at a lower frequency and then another when amplitude drops 3dB. In a well behaved scope this takes into account the usual "unknown" scope filter response, whereas the pulse technique does not. Not going to discount the pulse use tho, as a scope is a Time Domain instrument and usually used to measure pulses more, just as a SA is a Frequency Domain instrument and usually not utilized to measure Time Domain parameters, altho believe some do TDR by inference. All this begs the question, since SAs are specified over the frequency range of use (does anyone even know the pulse response of their SA?), why not specify scopes with pulse response rather than BW?? So instead of a 350MHz scope one would have a 1ns Scope, or whatever based upon filter characteristics :-+ Anyway, thought this was interesting, of course YMMV!! BTW seems the latest scopes are starting to move into the Frequency Domain more, things like high resolution and frequency range FFTs, Bode Plots and so on, very versatile instruments indeed ;) Wait, we have one of these scopes, well it's pretty good but not the latest 12 bitter, we need, must have, require, demand, requisition, ok we'll now start saving our lunch/beer money for one ;D Best, |
| tautech:
--- Quote from: mawyatt on February 25, 2024, 06:31:18 pm ---All one needs is a decent sinewave signal generator to measure scope BW, not necessarily accurate in amplitude just uniform across the frequency range of interest. It takes just two measurements, one at a lower frequency and then another when amplitude drops 3dB. In a well behaved scope this takes into account the usual "unknown" scope filter response, whereas the pulse technique does not. --- End quote --- Exactly. One I checked recently: --- Quote from: tautech on February 08, 2024, 04:13:19 am ---Data point for the 100 MHz badged SDS814X HD = -3dB BW ~155 MHz Source SDG6022X terminated into 50 Ohm feedthrough. Checked @ 10 MHz = 1V p-p --- End quote --- |
| Martin72:
At that time I had also measured a DHO804 with a 1V sine wave, whose -3dB frequency deviated only a few Mhz from the calculated value from rise time. That was probably luck/coincidence. |
| gf:
--- Quote from: mawyatt on February 25, 2024, 04:48:25 pm ---You normally don't see folks using swept frequency measurements to determine scope pulse response!! --- End quote --- The problem, of course, is that you would need both magnitude and phase response to do that. [ I would not rely on it being a minimum phase response in general. ] |
| DaneLaw:
Also use crude sweep, as none of the arb signal gens I got, can muster up in the 3 digits MHz, so I tend to use these relatively cheap signal gens from China that go up around 7Ghz (based on a max2870 synth chip). obviously not close to linear across that ludicrous wide-span but in the lower sub Ghz range, with a sweep, it seems to be relatively flat. (0-800Mhz sweep below) but there are likely tons of reasons why that is a problematic approach to use a 40-buck mashup RF device from the local Szhenchen flee market to measure BW.?? 0 to 800MHz span plot --- End quote --- --- End quote --- Dropping hard 6.5GHz, but both tools (RF siggen & SA4) are way out of useful amplitude tolerances at these higher GHz freq. Also tested the amplitude linearity with one of these self-contained 0 to 6Ghz RFpower meters that also hold a -32dBm selectable digital attenuator. --- End quote --- --- End quote --- |
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