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Review: Hantek DDS 3X25. Anyone own one?
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saturation:
Yes, I concur 'close outs' are my favorite deal purchases.  I will review it,hopefully also take time to post photos of it working to its maximum capacity.


--- Quote from: shafri on January 10, 2011, 06:10:54 pm ---
--- Quote from: saturation on January 10, 2011, 06:02:35 pm ---I wouldn't be surprised if it has ceased production and is discontinued; its been on the market since 12/2008.  But that's not necessarily a bad thing,

--- End quote ---
dont worry, the last batch usually is the most stable and cheapest.


--- Quote from: saturation on January 10, 2011, 06:02:35 pm ---Ouch!  I wish I had waited for your link, a lowest final price with S&H going via UPS is $111, $30 less than what I just paid just a few days ago.

--- End quote ---
dont worry, you can think later on how to gain that $30 back by using the device. possibly more.



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alm:

--- Quote from: saturation on January 10, 2011, 06:53:06 pm ---As I understand DDS, the final output stage is a reconstruction low filter.  How its made determines what harmonics and distortion will squeeze through.  As for arbitrary waves with different frequency characteristics, I'll have to play each as it occurs, doing what I draw and what I see comparisons ???.

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That low-pass filter is for the harmonics from the DAC, which is usually a fixed frequency.

I believe the difference between DDS and 'true' arbitrary waveform generator (as defined by the manufacturers of those) is that a true AWG runs the DAC at a sample rate equal to number of samples * repetition rate. DDS runs the DAC at a fixed frequency, and adjusts the samples to match. It has to interpolate or round the samples if the sample rate doesn't happen to be a multiple of number of samples * repetition rate. The advantage of DDS is that it can easily vary the frequency, for example for sweeping. This makes it also easy to implement a function generator. I'm by no means an expert on DDS or AWG, most of my knowledge comes from reading appnotes and datasheets/manuals. Some links: Tegam AN-401: True Arbitary Waveform Generators Offer More Than Function Generators with Arbitary Capability, Tektronix XYZs of Signal Generators.

Most cheap arbitrary waveform generators seem to use DDS, even though true AWG seems simpler to me. Maybe implementing true AWG is harder than it looks, or it's because they want to bundle a function generator. My guess is that the Hantek unit also uses DDS.

I added two attachments about filters for DDS. The first is from an ELV design for a 30MHz DDS function generator (no arbitrary waveform capability, but DDS is DDS). The DAC is in IC5 (AD9834), the signal is outputted on IOUT (Sig Bit Out is used for high frequency square waves, just ignore that part). ADG736 is just an analog switch. Depending on the type of signal, the Chebyshev filter (knee frequency = 34MHz) is used for sines (up to 30MHz), but bypassed for square waves (rise time is <5nS IIRC). The sample rate is 67.109MHz, well above 34MHz. The filter doesn't change with frequency.

The second is part of the HP 33120A service manual, a function generator/arbitrary waveform generator (DDS, 15MHz, 40MS/s). Depeding on the type of signal, it either uses a very sharp filter (ideal would be a brick wall response slightly above 15MHz) for sines, or a shallow filter for all other types of signals. Both filters have a fixed frequency response.
DaJones:
I just purchased one of these units, and it looks like I'm going to have to return it.

I get jitter on all waveforms other than sin, above 2mhz.

Here are some shots of the jitter, using the Rigol REF function to make it visible.






The Sync-Out also has a LOT of jitter and most of the time doesn't stay in step with the output signal ( depending on
the frequency ).

I'm hoping this unit is defective, and that a replacement might fix the issue.  But I can't find any reviews anywhere on the net.

Can anyone confirm that these units actually work and have stable signals?

saturation:
@ alm, thanks a bunch for those links, some reading to do!

@ dajones, ah!  you're the first to post some specifics about its frequency output.  Is this a 100 MHz Rigol?  Using a 10MHz square wave is at the limits of its frequency response, you'd have to set the scope at its best to reduce the effect of the DSO introducing its own jitter, making the measurement less stable.

http://www.edn.com/contents/images/6486046.pdf

Set the Rigol to peak sampling mode and increase the waveform amplitude, at minimum, has it helped?
DaJones:
I have a modded DS1052E ( 100mhz ).

I see the same terrible jitter on an analog Tek 2235 scope ( 100mhz ).

The jitter starts at around 2mhz and gets worse as the frequency goes up ( it may start sooner than that, but isn't noticeable, proportionally ).

The Sync-Out jitter is really bad. At some frequencies the jitter settles down, at other frequencies there seems to be no timing connection between
the Sync-Out and the output signal.

In fact, if I set the frequency to 2.5mhz, the Sync-Out is kind of stable ( though the output signal is jittery ). But if I step the smallest amount up or down in
frequency ( 2,500,000.001hz ) the Sync-Out signal looses all timing relationship to the output signal ( and is itself still jittery ).

I'm really puzzled by the fact that this product has been out for years now, and it's for sale all over the place, and yet I can't find any reviews or comments on it.

I'm going to have to ask the seller if he sells a lot of these, if he gets a lot of returns, etc.

If someone could confirm that this is a design problem, I wouldn't bother with an exchange and just get a refund.

So... is anyone with one of these units able to confirm a 10mhz stable square wave??
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