| General > General Technical Chat |
| Review: Hantek DDS 3X25. Anyone own one? |
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| Mechatrommer:
--- Quote from: grenert on February 25, 2011, 03:15:43 pm ---Dave was able to cause aliasing on the Rigol in his review of the new Agilent scope. --- End quote --- the better workaround for rigol is to use peakdetect or long memory resolution. |
| saturation:
All DSO have aliasing once your sampling rate is ~< 2x sampling rate used to view the signal. With the 1052e, and the 3x25, generate a 1 MHz signal, AUTO the scope and look at the 1 MHz waveform. Hit, MEASURE, select DISPLAY ALL. You'll see 1 MHz on the frequency counter that is measured on the actual waveform shown on the scope. Now, reduce the timebase to 20 ms. Hit HORIZONTAL -MENU to see the sampling rate used by Rigol, 10ks/s, 100x less than the input signal. You'll see a ~ wavery 15 Hz sine wave. --- Quote from: grenert on February 25, 2011, 03:15:43 pm --- --- Quote from: Mechatrommer on February 24, 2011, 05:58:36 am ---EDIT: well, i just quickly realized it. its not a bug, just my stupidity at using the dso. its called aliasing http://en.wikipedia.org/wiki/Aliasing so case closed. --- End quote --- Dave was able to cause aliasing on the Rigol in his review of the new Agilent scope. --- End quote --- |
| saturation:
Thanks bekir, replacing the op amp and knowing the 3x25 works well thereafter suggests the op amp alone was defective, and no something else causing it to fail. Sampling the same signal multiple times is a good way to cancel out the noise best, the scope's do the same via averaging. To measure the quality of the sine wave best requires a spectrum analyzer or a scope with a noise floor below -90dBc, a scope using FFT and an ADC of 16 bits or more. What are you trying to measure, the systems impedance, phase relationship and amplitude for a linear network? Its been a while since I did anything with gross calculations with FFT, IIRC primes just allows mathcad to use DFT and make processing easier. http://iopscience.iop.org/0957-0233/19/10/105102;jsessionid=A1AB9DB658381B0A964FEB3B70D6B429.c3 --- Quote from: bekir on February 25, 2011, 12:51:05 pm ---I've replaced it (LMH6702) myself, To get the response accurately, I was sampling at least 2 or 3 periods then using linefitting methods on matlab.That also decrease error induced by noise. But as I mentioned ? am not experienced in this stuff so I am open to any suggestion. As for the tests, I may ask for the technicians in EE labs for better equipment is you wish. --- Quote from: saturation on February 23, 2011, 02:29:19 pm ---Yep, we discussed using the Hantek as a source for making VNA calculations, I use Lissajou figures to make qualitative measurements for phase delay, we just discussed this, find our threads on measuring phase shifts and the Hantek. Your prime number test is interesting, to superimpose them, do you have multiple sine wave sources and measure simultaneously or did you send each prime individually then merge the waveform data? --- End quote --- I will check the thread right away. I have measured simultaneously. I have calculated voltage vs time in matlab then transfer it to DDS buffer. Maybe I can better explain by including part of the code: --- Code: --- freqs=primes(64); % get prime numbers up to 64, 18 in total for j=1:length(freqs); yy=yy+sin(freqs(j)*2*pi*i+freqs(j)); % add unit amplitude sine wave at each prime freq multiple end yy=yy./max(yy); % normalize to avoid saturation on output --- End code --- I have added constant phase shifts between signals, this way fft works better. (I fft'ed yy for both 0 phase and this case, amplitude values closer to each other in this case). --- End quote --- |
| bekir:
Thanks for the info on measurement of quality evaluation. I will ask ee lab. tech. for a better scope to test it. --- Quote from: saturation on February 26, 2011, 01:57:29 pm ---What are you trying to measure, the systems impedance, phase relationship and amplitude for a linear network? Its been a while since I did anything with gross calculations with FFT, IIRC primes just allows mathcad to use DFT and make processing easier. http://iopscience.iop.org/0957-0233/19/10/105102;jsessionid=A1AB9DB658381B0A964FEB3B70D6B429.c3 --- End quote --- What I want to measure at the end of the day is the complex capacitance of a sample. The reference is quite what I am trying to do. The difference in my setup is the measurement method. I am currently using "auto-balancing bridge method" as described in 10th reference in the paper (http://cp.literature.agilent.com/litweb/pdf/5950-3000.pdf). From measured voltages (magnitude and phase), impedance is calculated. I want to see if a material can be modeled with existing relaxation models such as Debye. |
| Mechatrommer:
am playing with synch out. tried the 6mhz and 7mhz as in picture. it seems like some software-like trick, or leap year style of trick, it will either shorten the valley, or longer the peak at some interval. i'm assuming it tried to reach the set freq as it only doing at some multiple of freq, when you set not in this multiple, then this leap year trick will happened. |
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