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| Review: Hantek DDS 3X25. Anyone own one? |
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| saturation:
Comments on bolded items: Yep, the harmonics are measurable to the limits of the Rigol's capacity. So at worse the Hantek is doing in the neighborhood of no more than 0.4%, about the 1/8 bit resolution of the Rigol. I looked at the distribution in dB too, but converted I can't go below~ -50dB. I also swept the timebase from end to end, looking for trouble. I checked views with all the various FFT windows: Hanning, Hamming, Blackman, to get the best view. The pics are just representative of the best and worst. Although the jitter is there, I think its effect is a bit overemphasized, it only matters when circuits are sensitive or nearer the jitter's frequency, such as using it to clock a ADC. Since it appears fixed, it becomes more rate limiting at high frequencies, at 2.5 MHz the jitter represents 5ns/400ns a 1.25% variation in say, the duty cycle of a square wave clock. But at 25 MHz, its 12.5%. Can't hurt when used as a signal generator for input emulation knowing this restriction. Formally, its effect can be thus: It can drive an ADC ~ 100kHz before the noise begins to rise above the ENOB limits of 50dB. http://www.analog-europe.com/en/understanding-ac-behaviors-of-high-speed-adcs.html?cmp_id=71&news_id=222901444&vID=35 I think the jitter is a pickup of the maximum clock frequency, 5ns ~ 200MHz, as the manual states, its just an educated guess. Being the maximum DAC clock speed, the Nyquist frequency is 100 MHz, so that's the ceiling on waveform generation. There does seem to be periodicity to the jitter, if you switch the acquisition mode to 'average' the jitter completely disappears, so its appearing at a fixed interval, like its frequency modulating the clock period. Yes, the manual is very superficial. There is no access to adjusting the clock period directly. As you pointed out before, the software has a demo mode, why they didn't make it available for download for promotion purposes is curious, but methinks they were afraid of criticism of its dullness and thus, kill 3x25 sales. Your AWG comments spurred me to examine it in detail. When selected, it takes the existing waveform on the screen, be it sine, sq, ramp etc., and enters editor mode. You can thus, mess up the waveform easily, as in the photo I left of a sine wave with spikes on it. I'll report on uploading a CSV file later. --- Quote from: alm on January 13, 2011, 02:09:53 am ---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. --- End quote --- |
| saturation:
More tests of the Hantek. The first image is a small clock output pickup from the sync output. This contamination could be the source of the jitter. The next 2 are simulated RC discharge outputs. AWG: The Hantek wave drawing software has very few timsaving options but as is, its very useful. Its as easy as drawing with a mouse; its better with a pen stylus. Users need to save work as soon as done, because if another waveform is selected by error, the drawn waveform is deleted without warning. I imported Rigol 1052E waveforms into the Hantek. The CSV files are not drop in compatible. To get the correct format, save any Hantek CSV waveform, open it and overwrite its data points with the datapoints of the Rigol, just insure data is on the same scale and format, which can be done easily with Excel to format a column's properties. Hantek cannot import wfm files saved by the Rigol. I'll report if externally generated wfm files can be converted to CSV without incompatibilities. That said, the Hantek can generate complex waves, but the AWG output is limited to 100kHz tops. depends on the complexity of the Arb and the MCU capacity to output it fast enough to meet the frequency you enter. Below are samples of simulated cardiac waveforms I drew, these are typically complicated after heart attack types, which requires good frequency response to reproduce. The first show a realistic rate of 60 Hz, or beats per minute, using the Rigol 1052E roll mode for sweep. The same cardiac waveform running at 100kHz and 10kHz, all without noticeable distortion. Other AWG output: Noise burst detail, zoomed in from a single pulse. These were captured at 1Gs/s at 10us and zoomed in to 1us. Noise burst, as a pulse at 10us. Finally, a complex waveform, mix analog digital with various levels. The complex waveforms are challenge to get the 1052E to sync properly, but it did with with rock stable accuracy with manual tweaking. |
| saturation:
You're welcome. Shafri, maybe this thread has to be moved to reviews, as it began as an inquiry, but it became a review. I'll rewrite the specs into a table format so its summarized. Although I have a few more tests to run, frequency stability being one, I think based on what is posted to date, I could summarize it: The Hantek DDS 3x25 is a solid function generator with arbitrary waveform capability, far better in performance than most analog function generators, in its price range or with similar specifications. It one of the lowest cost 25 MHz capable DDS function generator on the market, and likely the only one with AWG capability. The 3x25 is down -3dB at 25 MHz, but is usable to 75 MHz, at -12dB, for sine wave only, with the same distortion+ noise limits. It can be found typically for $150, but Saelig still has it for $100, +10 s/h. Its a sleeper, so it can be found for a steal. --- Quote from: shafri on January 17, 2011, 06:19:21 pm ---good work! --- End quote --- |
| saturation:
I've completed frequency accuracy and stability measurements using a 4ppm B&K 1870 frequency counter. Conditions: 70F, 25% RH, ~ 1025 mBar. Specs of the test equipment: http://www.bkprecision.com/products/model/1870/handheld-frequency-counter-12ghz.html Hantek Tests: After 24 hours stability is 2.00 ppm. 1 hour stability is 0.60 ppm. Accuracy against the B&K, rated at 18.01 <= 200 ppm. This is better than specifications mentioned in the manual, and stable for ~ 24 hours. |
| DaJones:
--- Quote ---The Hantek DDS 3x25 is a solid function generator with arbitrary waveform capability, far better in performance than most analog function generators, in its price range or with similar specifications. It one of the lowest cost 25 MHz capable DDS function generator on the market, and likely the only one with AWG capability. --- End quote --- Man, I don't understand how you can say that! The thing glitches like crazy for square waves above 2.5mhz ( except a few stable spots like 10mhz ). The sync out line has no timing relationship to the output signal except at those rare "stable" spots. The sync out line glitches every 20us ( 50khz ) and will glitch any output waveform other than sine waves. I could NEVER recommend this to anyone, except maybe as a source of sine waves, and as long as you didn't need to use the sync out line at all. If you did your stability test at one of the "stable" spots ( like 10mhz ) you might want to try it again at 10.1mhz. |
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