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Review: Hantek DDS 3X25. Anyone own one?
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tinhead:

--- Quote from: Mechatrommer on February 23, 2011, 12:24:16 pm ---the usb chip, main mcu and another chip after it have been erased.

--- End quote ---

well, you don't have care to much about ... the usb chip is STM32F102Cx or STM32F103Cx
acting as USB->i/o controller (you can see in driver description and a clear ARM JTAG interface),
the one tsop chip no idea for now, probably just a buffer/voltage converter
and the big chip is Spartan 3AN. Originally it was designed to use 3A , there is still empty
place near J2 (FPGA JTAG) for config ROM.

Probably Hantek decided to use Spartan3 AN because of the integrated flash to prevent
clone-makers from cheap clones (the hardware costs only few bucks),
maybe they did it after someone already cloned (and then removed of course external config ROM) - if so
it would be cool to get older revision with config rom soldered (U1).

No matter now, just be carefull, if you shot this chip you can buy a new DDS.

EDIT:
@saturation
you don't have to ping the JTAG anylonger, we know now what soldered (well actually you can take a look inside, maybe you have old revision ...)
Mechatrommer:
you are welcome saturation. anytime if you want the fullscale image, just PM me, or if you want specific part of interest to be photographed, just ask, i'll be glad to take it for you to the best of my lens and skill ;). in the mean time, i just put it back in its clothing. @tinhead. i'm not capable to tinker with jtag or spartan, so i think i just use it as is. thanx for the info though, who knows i might have idea in the future.

any idea whats most probable causing the jitter in square wave at higher freq? i confirmed the +-5ns jitter. my speculation, its in the software, but i dont know. my speculation is based on the fact that this unit is using sample data to generate signal, not true "hardware generator" such as sin generator chip etc, so jitter might come from inconsistent (codelength) sample feed to the buffer/voltage converter etc. but still, i've not look/analyze the circuit detail enough and i'm not master in hardware, i just assuming based on my experience/background.

any good reference on how to convert (or the theory) this to network analyzer? i think i want to do this as an exercise when i got time.
saturation:
Hantek made this forum available with a new URL, for tech support:

http://www.hantek.org/asken/iasklist.aspx?cid=I00011&state=2


Tinhead@ : thanks for those quick tips, I'll use that to check into the chip eventually.

mechatrommer@: you're welcome, if you find other interesting things with the 3x25, let us all know.  Your idea on the jitter is possible.  You can import the output waveform into the arb section by first selecting a fixed waveform, like sine, then hit the arb button, and it will show you all the data points.  So far, I haven't been able to find anything wrong with their sample, but let us know if you can improve on it!

As a 'network analyzer' all you do is check the phase, amplitude versus frequency of a system at higher frequencies.  I described it earlier with the Lissajou figure. 
bekir:

--- Quote from: saturation on February 23, 2011, 02:29:19 pm ---Thanks bekir, when you replaced the signal generator that broke, did you repair it yourself, or bought a new 3x25?
I see from mechatrommer's photos the op amp is a LMH6702 and the comparator is TI TL3016; that's a pretty good op amp by the way.
To prevent further damage in high output tests you can put another op amp infront of this op amp and isolate it, just configure it as a voltage follower.

--- End quote ---

I've replaced it (LMH6702) myself, due to our limited budget I had no other option by that time. Input of the op-amp was giving the right waveform but output was shorted to ground. Maybe it is not the best way to not the degrade the performance, but I had only soldering iron at hand (I work in mech.eng. lab so we don't have reflow station or as such), so I hand soldered it. As you mentioned adding buffer will be the best option.


--- Quote from: saturation on February 23, 2011, 02:29:19 pm ---From your tests, did you check the quality of the sine wave output on any higher end equipment you have in your lab?  Particularly, what is the harmonic output of the sine waves; I'm just curious.  I only have a Rigol 1052e but I get nothing at its noise floor which is about -50 dBc.  A more sensitive instrument might show that the sine wave output is hifi audio quality, i.e., -90dBc or more.

--- End quote ---

I checked the output with an OWON oscilloscope which can not be a real measure i think. Also I have checked with Hantek DSO-2250 (100 mhz bw). Up to now I was using single frequency sine wave. 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).



grenert:

--- 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.
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