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Review: Hantek DDS 3X25. Anyone own one?

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torch:
The following were taken controlling the output with the Hantek supplied software then the Goltek version. Frequency set to 20Mhz, voltage output set to 3.5v.  Input set to 1x. and the DDS 3x25 connected to a modded Rigol scope with a BNC cable and 50 ohm terminator tee.  "Auto" setting used then persistence turned on to show overall effect.

Hantek software, "white noise":



Hantek software, "gaussian noise":



Goltek software, "noise":



Goltek definitely seems less random at those frequencies. Hope this helps.

asbokid:

--- Quote from: Mechatrommer on October 29, 2012, 10:40:28 pm ---goltek will not be able to create white noise for you, its only to send arb signal to dds3x25, try using tektroniks ArbExpress to create white noise. if you really serious about white noise, the 3x25 memory might not be enough for you. do you mean your white noise requirement really maxed to 20MHz?

--- End quote ---

Well it's for VDSL2 CPE modems which in the UK use sub-carriers up to 17.5MHz, iirc.  The ITU G.992 training period during which the background noise is tested lasts for a minimum of one second (but the test is usually repeated at least once).  So, as you point out, the DDS 3X25 Sample Memory which can hold just 4KSa isn't big enough. And however random that sample set is made to be, it will still end up being repeated many times over during that one second or more of testing.

The alternative, sfaics, is a US$5000+ piece of equipment, with 256MBytes of fast RAM.  A price that is way beyond the budget for a project that is being funded by, erm, me!   :'(

I don't understand why this equipment is so expensive.  The Application Note accompanying the Maxim series of high-speed DACs [1] describes the functional architecture of an Arbitrary Waveform Generator.  It doesn't look that expensive.  The DAC itself costs at most US$30.


Though, presumably a high-end MCU would be needed to clock in 14-bit samples at 200Ms/s or more. Over at dangerousprototypes, they started chatting about building an AWG, but the initial enthusiasm fizzled out and nothing materialised.  Is it within scope of the hoi polloi?!

cheers, a

[1] http://para.maximintegrated.com/en/search.mvp?fam=hsdacs&tree=master

torch:
Is it important that the noise is completely random? Noise usually covers a wide range of frequencies, right? Two thoughts:

1. utilize Goltek's sweep function to cover, say 1KHz to 25MHz with a 1ms step interval and the "noise" (or a custom) waveform.

2. write some software to feed the DDS 3x25 with a constant stream of new waveforms from the computer to get around the memory limitations.

asbokid:
heh, Torch!

Thank you very much for going to the trouble of posting these.  You've made the device all the more tempting!

cheers, a

Mechatrommer:
for random data like this it will boil down to memory size and clock speed. as far as 3x25 is concerned it has 4096 bytes memory and 200M sample/sec thats the limit when you put in your calculation. at that clock rate, you can put in some 100MHz harmonics (not random) and then add up lower freq harmonics etc and so on. if you calculate 4096 samples at 200MSps, that is a 48KHz repetition. from there you'll decide whether 3x25 can do the job or not.

as for goltek, it will "normalized" and "centered" the input data so you may get somehow sometime attenuated signal. agree with torch you may want the original hantek software to produce random data and send to 3x25 to see the difference.

tell you what, if you are sceptic about 3x25 buy, you may send us (or me?) the ArbExpress data to be produced in the 3x25, we'll (or me? whioever comes first) provide signal output capture just tell us which portion you are interested in or we may capture the portion we're interested in ;) bear in mind 3x25 only maxed to ±3.5V magnitude (mind is modded to ±10V) take that into consideration when normalizing or generating your data (i can renormalized your data to suit).

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