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Review: Hantek DDS 3X25. Anyone own one?
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asbokid:
That's a very generous offer, Mechatrommer! Thank you!  You've opened up another issue.  I don't even know what sort of amplitude of noise is required.   I'm basically replicating for VDSL2 some earlier tests done on ADSL2+ CPE.    All sorts of issues to tackle yet - matching the impedance of the noise injector with the transmission line, while limiting the attenuation, removing or adding the -48v DC bias on the line, etc.

How did you mod yours for +/- 10v ?

cheers, a
Mechatrommer:
most of us are not expert in your VDSL area so we cant help on that and what kind of noise requirement you need, that one you need to figure out your self. we use 3x25 for different purposes from one person to the other.

--- Quote ---How did you mod yours for +/- 10v ?
--- End quote ---
put gain amplifier at the output, i hacked the trace and put it in between, that will invalidate the warranty ;). gain opamp info is everywhere you may find so i will not elaborate and claim to be an expert... here may help... http://www.soasystem.com/eng/goltek/amplifier.htm except i embedded it into the 3x25 already so its now permanent.
saturation:
Having access to an ovenized 1996 Racal Dana counter stable to .001 ppm I retested the 3x25 frequency stability and was surprised that it easily did 0.1ppm over 6 hours.  By comparison, in the same period the more reputable SFG1003 Instek generator was 1ppm until after 1 hour warm up, then they were on par.  Another plus for this el-cheapo.
zibadun:
Finally wrapped my head around using the hantek DLL from a python script. I need to generate a sweep with a step of about 25 kHz  from 1 to 30 MHz. The exact phase and frequency of each step is not important but I need the amplitude to stay as constant as possible through the entire range (into a 50ohm load). Can somebody please point to a post that I need to pay attention to implement this sweep?
marmad:

--- Quote from: zibadun on December 13, 2012, 07:25:57 pm ---Finally wrapped my head around using the hantek DLL from a python script. I need to generate a sweep with a step of about 25 kHz  from 1 to 30 MHz. The exact phase and frequency of each step is not important but I need the amplitude to stay as constant as possible through the entire range (into a 50ohm load). Can somebody please point to a post that I need to pay attention to implement this sweep?

--- End quote ---

I was again playing around with coding sweeps on the Hantek just the other day (after Dave's Bode plot post) and I have to say, it's difficult to get perfectly smooth ones. The problem is that there is no published or documented way to change frequencies exactly at zero crossings - so the frequency might step anywhere along the waveform (the number of possible commands in the DLL is really rather abysmal.). Somehow Hantek manages to do them smoothly from the DDS-3X25 control software (although not logarithmically), but I haven't been able to figure out how - perhaps it's time to try a USB protocol sniffer and figure out what that software is sending to the device for certain commands. I was incorrect - the Hantek doesn't do smooth sweeps either.
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