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| Review: Hantek DDS 3X25. Anyone own one? |
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| saturation:
Thanks dajones! Intended to do that to, will put that on my to-do test lists. Any more ideas, are very welcome. --- Quote from: dajones on January 12, 2011, 09:43:24 pm --- --- Quote ---I confirm dajones posts, there is a persistent jitter of 5-8ns most obvious in the square wave output. I haven't tried mitigating it, or trying a whole suit of tests, and will post a more detailed review later as I find time. --- End quote --- : / I was HOPING that it was just 'my unit' that was having this problem. You might want to take a look at the "Sync-Out" problem. If I set my unit to 2.5MHz, and display the output signal on one trace, and the Sync-Out on another trace ( on the scope ), I see that they are in step and not much jitter on the sync line. If I bump this up or down in frequency by a small factor ( 2.51MHz or 2.5000000.001 or 2.4999 ) the Sync-Out signal gets so jittery there doesn't seem to be any timing relationship between the two signals at all. --- End quote --- |
| alm:
--- Quote from: saturation on January 12, 2011, 10:58:19 pm ---Its a big problem with the Rigol's inherent noise and the potential for artifacts caused by the FFT itself, as we've discussed on eevblog in the past. Its a reason I'll post scope images more than discuss it [ its also easy to do with the 1052E], you can see the signal vs harmonics+ noise for yourselves. I also analyzed the maximum amplitude on FFT to see whatever harmonics are there and sometimes, not always, pick up a few distinct frequencies spiking over noise. So far the noise floor and/or specific frequencies are <= 1-5 mVrms for a fundamental at 1.4Vrms. That's ~ <= 0.36%. --- End quote --- That would be around -50dB, much better than the specs, but nothing extraordinary for DDS. 0.36% is at the very limit of the 8-bit dynamic range of the Rigol, so I would be suspicious. Setting the vertical scale to dB (assuming the Rigol supports that) would make it easier to see, although it doesn't change the dynamic range obviously. I would also set the sweep speed to a higher setting to get more horizontal resolution on the FFT for looking at the first few harmonics. For more accurate measurements, something like a notch filter might help. Glad that it appears to perform better than expected, except for the jitter issue. I wonder what kind of change takes place above 2.5MHz, different DAC frequency? 200MS/s and 4kS waveform memory means that the full memory depth can only be used up to 50kHz, so they have to be down sampled above that. Maybe there's some rounding/dithering error there? At 2.5MHz, there will only be 80 points per period, so even minor changes will be significant, especially for something like 2.6MHz, which is not a divisor of 200MHz. Any idea if there's some periodicity to the jitter? If they run the DAC at 200MHz, and alternate periods of 38 and 39, that would generate some jitter. The manual is useless, as expected (good thing you don't need one), so it provides no clue how it changes the output frequency and what it does with the extra points. After looking through the manual, I wonder if the arbitrary waveform capability is as bad as it looks? From what I see in the manual, you're forced to edit each individual point individually (if it has more features, it's not mentioned in the manual). I thought the Rigol software was bad, but this seems completely useless. Like Rigol, the compensate for this by leaching on the software that their competitors make available for free. Guess you can't expect them to write their own software for this kind of money. |
| saturation:
Hi Alm, As always, your posts require a lot of thought for a reply to very insightful points. A prelim. The AWG software is crude as you begin with a bitmap image with 1000+ points, moving each point with a mouse will take a long time, so you are right, using some other makers editor is the likely solution, limiting the 3x35's software for touch ups and sending it to hardware. This Hantek uses Tek and CSV format. This allows importing other images. Also, the Rigol exports to CSV so captures can be used too. I haven't given the AWG component a detailing, so only know these superficially. I am still characterizing its built in waveforms, but I have tested AWG output and so far so good. Clearly, the manual's spec sheet, listed on this thread, is wanting. But the great news is that the device is performing >= spec sheet, and we are discovering others specs, many are good and less good, i.e., jitter. I'd bet the "variable" clock design creates more jitter than needed. But jitter is a weakness in DDS designs for more than just the clock; one reason the Instek 1003 is nice, its more solid a signal reference, none measurable by the Rigol. It not a problem for design or testing work if your design isn't picky about duty cycles, or operates at speeds under the jitter variation, in this case 8ns or 125 MHz. http://www.eetindia.co.in/ART_8800549886_1800002_AN_4307fcee.HTM http://electronicdesign.com/article/communications/jitter-and-its-measurements3781.aspx http://www.maxim-ic.com/app-notes/index.mvp/id/377 Interestingly, few devices specify jitter, and reading on it more, seems like even the measurement standards are evolving. Aside, maybe the 'waveform distortion' spec really meant MHz not kHz, because that -50dBc is so coincidental. |
| saturation:
Here's the key component review in pictures. First pair of images are the Instek 1003 response to its maximum output, basic sine waveform and FFT spectra and next followed by the Hantek sine and spectra. You can see the absence of any visible harmonics, prior to magnification, to be show later. Next pair is a square wave from Instek vs Hantek Sq. wave. CurA marks the 17th harmonic, at 51MHz, and CurB marks the location of a large spurious harmonic, visible with magnification, on the noise floor. The noise floor of sine wave magnified including a spurious high frequency component. 2.48mV/1Vrms gives the noise ~ 0.248%. The spurious high frequency is about 12mV or 1.2%, its ~ at 250MHz. The jitter close up, at 5.20ns. Hantek's maximum frequency at 75 MHz sine, with FFT spectra, clean at 75 MHz, with the Rigol at highest gain, and image stabilized with averaging [I use a 1052E unmodded, bandwidth of 50 MHz.] Sample AM modulation. Magnified noise floor on FFT at 40 MHz sine, from the Hantek. Note the 5mVrms spike at 458 MHz, CurB. Sample of my AWG output, a sine wave with negative and positive voltage spikes, and its spectra. |
| saturation:
Sample FM Modulation image. |
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