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| Rigol DHO804 Test and Compare Thread |
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| 2N3055:
--- Quote from: Randy222 on December 27, 2023, 03:06:45 pm --- --- Quote from: Martin72 on December 26, 2023, 08:15:27 pm --- --- Quote from: Randy222 on December 26, 2023, 06:53:28 pm ---On the DHO804, why does the scope lose signal sync if the vertical scale is increased? Example; Ch1 on the internal 1kHz 3v peak signal, set trigger to 1v, but then dial up the scale to 10v/div. The trigger does not change, so why the scope lose sync on the square wave (dancing signal)? --- End quote --- Have a look at the data sheet under "Trigger Sensivity". It says 0.5div, at 10V/div and a 3V signal it is no wonder why it no longer triggers. --- End quote --- Trigger is based on the display? If the signal is 3v and the trigger is 1v, why should it matter what the V/div is set to? --- End quote --- Trigger is not based on display. Even on analog scope minimum signal amplitude for reliable triggering will be based on certain percentage of dynamic range, i.e. input sensitivity. Ths scope has digital trigger. It works on signal after ADC has sampled it... So if you have signal that is less than step of ADC you cannot trigger on it, right? And of course you don't need only few steps of ADC, because you need hysteresis, and enough sample points to interpolate curve through trigger point with enough accuracy... |
| Randy222:
--- Quote from: Martin72 on December 27, 2023, 05:12:08 pm ---I have just tried this on the 1104X-E and it is exactly the same. But it makes no sense, you can hardly see anything of the 3V signal at 10V/div. --- End quote --- Try 5V/div 1V trigger, which fails to sync on the Rigol. The signal is the signal in the front-end, trigger setting is relative to signal, so why can't it display it, even if squashed in the display, a 10V/div makes a 3v signal look almost flat on a small 7" screen. What if the actual screen size was 14" with same number of div boxes making a div box physically bigger on the screen, that squashed line on 7" screen suddenly is not so squashed on a 14" screen. Is it just that it did actually trigger but the device can't paint it to the screen? |
| ebastler:
--- Quote from: Randy222 on December 27, 2023, 06:21:42 pm ---The signal is the signal in the front-end, trigger setting is relative to signal, so why can't it display it, even if squashed in the display, a 10V/div makes a 3v signal look almost flat on a small 7" screen. What if the actual screen size was 14" with same number of div boxes making a div box physically bigger on the screen, that squashed line on 7" screen suddenly is not so squashed on a 14" screen. Is it just that it did actually trigger but the device can't paint it to the screen? --- End quote --- I'm afraid you are on the wrong track there. Yes, "the signal is in the front-end". But it is then amplified or attenuated according to your V/div setting, A/D-converted, and the trigger engine works based on those digital data. If you change the V/div setting, your "trigger setting" does indeed not change: As mentioned before, the trigger threshold you have set will remain unchanged. (I.e. the scope will adjust its ADC count value for the trigger threshold, such that the trigger threshold's voltage remains unchanged.) But the trigger hysteresis, i.e, the signal swing required to detect a "significant" crossing of the trigger threshold, will change. The hysteresis gets larger as you go to higher V/div settings. That makes sense from a technical perspective: The scope cannot determine an accurate trigger time from just a few ADC counts of signal swing. |
| Martin72:
Finally... After excactly 3 month of testing my conclusion, only from my point of view, of course. Summarized in pros and cons: +Very compact housing with external power supply unit. +Sharp 7" display with high resolution +Very low noise, native 12 bit vertical resolution +Very clear, easy-to-use user interface. +Unique window function in this price range and far beyond. +Easy to hack +Inexpensive -Touch function in the screen size can no longer be used only with fingers -No hires mode (14, 16 bit) -Sample rate drops to 312.5 MSa/s from 3 active channels, must be kept in mind when displaying high-frequency signals -No bodeplot -Memory drops to a meager 1Mpt when all channels are active(original state) -Few decoding functions -No upgradeable options(original state) -Relatively useless "ultra acquisition" mode -Poorly equipped FFT function, also error-prone -Various inconsistencies in the software in general -Only one usb port -Somewhat high-frequency sounding fan -Limited window functions As I said, just my impressions, I won't compare it with other scopes. Some, if not many negative points could easily be corrected by rigol via the software, but unfortunately we all know that probably won't happen. Instead, the users (Turbotom, FFT) have to fix their bugs - very embarrassing. But that doesn't mean that you can't work with these scopes, of course you can. After the first firmware update, I didn't experience any more crashes. And if you don't need a bodeplot and only rarely use FFT, then it's a good scope with some innovative new features compared to older models in this price range. But if rigol does nothing more to the scope and if the SDS800X HD becomes available on the world market, at a similar price, then it will be very, very difficult to find reasons to buy it, except perhaps that you wouldn't buy anything from the competition. But it's not currently available, so the DHO800 is the choice if you don't want an older entry-level scope. That´s all folks, thanks for reading. Martin |
| Randy222:
The FFT cal file is fixed using the info from the DHO1000 thread. |
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