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| Gw Instek GDS2204E (200MHz 4 channel DSO) review |
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| rhb:
--- Quote from: Mortymore on March 31, 2019, 10:50:23 am ---Having played a bit with the Spectrum Analiser option, after "re-upgrading" my 2074E from 200 to 300MHz, found that the higher frequency that can be set is 750MHz, but the span remains the 500MHz (so it has to start at 250MHz). Though it may seem a nice feature having the ability to shift the frequency range 250MHz up, it actually has no use since there's nothing shown in the display above 500MHz (see picture attached: GW2000E_SA_750MHz.PNG). Am I doing doing something wrong? Is that a bug? Or am I missing some useful point for this to be like it is? --- End quote --- The 750 MHz label is a FW bug. It cannot go above the 500 MHz Nyquist frequency. And the anti-alias filter limits it to around 350 MHz *if* they designed it properly. It gets quite difficult to devise test cases. FWIW the step response using a 40 ps rise time square wave is exactly the same for the 200 & 300 MHz settings. I need to do some more testing, but at the moment I'm playing with a Tek 11801 sampling scope in preparation for measuring actual clock skew in the Zynq vs what Vivado calculates. The SD-26 heads sitting at the post office have a 20 GHz BW. So I'll be able to look at the skew of all the 8 data lines in a PMOD port to a resolution of 2-3 ps. |
| nctnico:
--- Quote from: Mortymore on March 31, 2019, 03:03:07 pm --- --- Quote from: nctnico on March 31, 2019, 12:43:26 pm ---BTW if you look at the SA screen you'll see it stops measuring at 500MHz. --- End quote --- That's exactly my point. What's the purpose of extending the SA up to 750MHz if it's useless above 500MHz? I would call it a bug. Reminds me a speedometer with a scale up to 220Km/h in a car that only reaches 160. >:D --- End quote --- It is not a bug. How can you get the maximum frequency in the center of the screen otherwise? Regular spectrum analysers usually allow similar settings. @rhb: I have measured an increase in bandwidth on my GDS2204E after the 300MHz upgrade (IIRC from 270MHz to 320MHz) but it is probably too small to really see in the step response. |
| rhb:
--- Quote from: nctnico on March 31, 2019, 05:01:34 pm --- --- Quote from: Mortymore on March 31, 2019, 03:03:07 pm --- --- Quote from: nctnico on March 31, 2019, 12:43:26 pm ---BTW if you look at the SA screen you'll see it stops measuring at 500MHz. --- End quote --- That's exactly my point. What's the purpose of extending the SA up to 750MHz if it's useless above 500MHz? I would call it a bug. Reminds me a speedometer with a scale up to 220Km/h in a car that only reaches 160. >:D --- End quote --- It is not a bug. How can you get the maximum frequency in the center of the screen otherwise? Regular spectrum analysers usually allow similar settings. @rhb: I have measured an increase in bandwidth on my GDS2204E after the 300MHz upgrade (IIRC from 270MHz to 320MHz) but it is probably too small to really see in the step response. --- End quote --- My 8560A sets the center frequency to 2.9 GHz, but issues an error message that 30 Hz RBW is incompatible and basically does nothing. It's an analog instrument, so a bit different. An upper limit above Nyquist on a DSO is just simply silly. It's neither possible nor useful. Like the Instek FRA app, it's a demonstration that the programmer didn't have a clue what they were doing. Were those the -3dB points? I've not tested it with my 8648C calibrated against my 438A. |
| nctnico:
These are the -3dB points I measured (the numbers are from the top of my head so please look up a previous post to verify). And again I don't think it is silly to end the trace half way the display. On spectrum analysers the center frequency is often used to have the frequency of interest in the middle of the screen so it is very easy to see where a frequency component is at. If the trace would be stuck to the right side of the screen you'd have to 'count squares' or or use the cursors to figure out what frequency you are looking at. The way GW Instek has implemented it is just convenient to use. The scope isn't trying to measure anything over Nyquist. |
| Mortymore:
Thanks for your clarification nctnico. Let it be this then: --- Quote from: Mortymore on March 31, 2019, 10:50:23 am ---.. Or am I missing some useful point for this to be like it is? ... --- End quote --- |
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