General > General Technical Chat
Review: Hantek DDS 3X25. Anyone own one?
marmad:
Well, as I start to play around with controlling the DDS-3x25, I start to realize why it is so much cheaper than other devices in the same range. I hadn't really looked closely at the software before, but now it starts to become clear.
I don't think the Hantek could be described as true DDS (Direct Digital Frequency Synthesis) at all - that is, if you define important processing blocks like a phase-accumulator and a waveform look-up table to be integral parts of DDS. The Hantek is lacking those things, but it seems it tries to mimic those functions (which should be in hardware) with the upper level software. Hence the source of the glitching and the jitter and the lag times.
Mechatrommer:
yes its just fpga, dac and an op amp. do you have link to a proper DDS architecture?
marmad:
--- Quote ---do you have link to a proper DDS architecture?
--- End quote ---
Link? you mean like: http://zone.ni.com/devzone/cda/tut/p/id/5516 - or - http://www.analog.com/library/analogDialogue/archives/38-08/dds.html - or - http://en.wikipedia.org/wiki/Numerically-controlled_oscillator ?
I didn't understand exactly what the Hantek was doing until I started trying to control it. I thought they had implemented the phase accumulator inside of the FPGA. Whoever designed the circuitry and wrote the firmware for the Hantek are idiots! The functions are so badly implemented; I thought you could at least set a sample length (up to 4096) and a frequency - instead, it tells you how long the sample length has to be! Plus, there is no direct control of the clock or a lookup table or... well, pretty much all the stuff of DDS. But you already know all of this.
They aren't really being truthful in their promotional material; for example, the manual says:
"DDS-3X25 adopts the DDS technology so that it has the advantages of high frequency accuracy, high waveform resolution, high reliability, and wide software support."
Now I have to decide whether to keep it or resell it and get the Velleman, which is true DDS (see attached block diagram), but slower, and costs about € 15 more.
Mechatrommer:
oo ok. quite a rant, if you happen to get the velleman, dont forget to do a review and tear down ok? ;)
btw, what do you expect the black box (below) will be, ie the phase accumulator, look up table and frequency selector (in another link)? a bunch of discrete components? or another specialized chip?
and yes i agree, their firmware and pc software writers are idiot they dont have a clue on signal generator usage, no user frequency tunable while maintaining waveshape, and the DDSSetFrequency returns strange number of points value to be used, it doesnt use full potential 4K points, mostly only half of it. but there's workaround for the later, ie you can pass the DDSDownload with any number of point you want up to 4096 points, but the drawback you have to calculate the Output frequency will be on your own and not in synch (your hack might give some hope). on hardware side i'm not sure about their idiocy, but i believe its the simplest design we can have, hence probably the cheaper price albeit high frequency capability, since i've made a tear down photos and not get any bad reply from experts. rufus here did teardown photos on his £900 AWG showing proper circuitry.
btw off topic, while looking for logic analyzer, hantek also got LA5034, 34 channel at whooping 500MSa/s, $200++ reused their 3x25 housing just different printing. i wonder whats inside, maybe just another fpga feed by 34 LA input. dont ask about their SW crappiness, its proven here. but will it be a good buy? if we really need a fast sampling LA? i dont know but i would like to hear some advice.
http://cgi.ebay.com.my/34CH-500MHz-USB-PC-Digital-Logic-Analyzer-HANTEK-LA5034-/310278713967?pt=BI_Analyzers&hash=item483e0d726f
marmad:
--- Quote ---oo ok. quite a rant
--- End quote ---
Ha, ha... yes... up too late last night frustrated with trying to control the damn thing. But I'm back at it today - testing some more ;D
--- Quote ---btw, what do you expect the black box (below) will be, ie the phase accumulator, look up table and frequency selector (in another link)? a bunch of discrete components? or another specialized chip?
--- End quote ---
Definitely hardware -- it can just be a cleverly programmed FPGA - that's how Velleman does it - their schematics are public and published. That's why I thought that the Hantek did something similar.
--- Quote ---and the DDSSetFrequency returns strange number of points value to be used, it doesnt use full potential 4K points, mostly only half of it.
--- End quote ---
Yes, when you use DDSSetFrequency, it actually sets a clock divider (immediately) then tells you what sample length to create for that clock rate. But I thought we could get around the latency problems a bit by creating a lookup table in software memory, then just appplying amplitude and offset before DDSDownload. What do you think?
--- Quote --- on hardware side i'm not sure about their idiocy, but i believe its the simplest design we can have, hence probably the cheaper price albeit high frequency capability,
--- End quote ---
Well, as I mentioned above, they could have programmed their FPGA for true DDS - but you're right that they probably couldn't have gotten the high speeds if they had done that. And I think for the sales, they were just interested in the highest speed numbers - not true or perfect DDS.
--- Quote ---btw off topic, while looking for logic analyzer, hantek also got LA5034, 34 channel at whooping 500MSa/s
--- End quote ---
Yes, I saw this... check your messages for more.
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