>> AWG 33522A ?
i can't compare only based on paper specs because from papaer specs, as you said, they equal.
>> I believe that the AD9747 should be quite a performant DAC if used correctly?
it is 16bit DAC, so it will be good at least for (without reading any datasheet) for 12-14bit. The noise floor on Hantek didn't looks like 12-14bit (how it looks with 14bit gear, one can see on RFasic pictures) but as 10bit. Sure, that pictures taken on modified device (this is why i was hoping to see pictures of what Hantek can do when set to within its specs, and when set to what it was calibrated for).
>> Regarding simple hardware modification, what would you think of an OCXO mod with a Micro Crystal OCXOVT-BV5?
in principle it does matter what clock source has been used for FPGA (better source=better clock output, but still, the xxx ps jitter created by switching logic and/or PLL within FPGA is added on top of that), an OCXO will for sure be better than current TCXO.
But the main reason for OCXO is frequency stability, not noise floor/jitter. Sure, when one replace ordinary XO with an OCXO (and probably do the necessary calibration!) the improved signal quality will be directly visible even on an DSO. But here is already an (VC?)TCXO installed, so the only improvement will be in the frequency stability.
>> I don't mind spending some bucks to modify the Hardware of the HDG2002b
I can't give any recomendation for changes without the actuall hardware. I would not run and buy parts, except they
are obvious or cheap (when known what TCXO has been used one can select better OCXO, they can costs lot of money. Or these
parts for counter, they costs "cents", so not a big deal).
What I would do is to:
- check first if the clock is really generated by FPGA (from pictures it looks like it is), if not, think wtf wrong here?
- measure (and at least check) how the DAC clock looks like
- is it variable?
- what is the rise time of the dac clock
- make reference spectrum snapshots of signal within and above AWG specs, with modified and unmodified device
- as above, but wit external clock connected to DAC directly (caps to be removed first, watch the DAC clkin level specs!)
- do measurments and spectrum snapshots before and after the output amp/filter/attn/what so ever there
(it might be interessting to see if there is any distortion coming from that part of the circuit)
- check the power rails. Hantek is chinese company, and these AWGs didn't costs enought to follow every design rule
(chinese eng. are very creative! but when design is price driven they tend to be too creative), so for sure here and
there are not enought caps, maybe better filtering, etc. But i would not just buy huge low ESR caps,
this is the wrong/useless step. They only good when needed and not everywhere.
- check if display have any influence on signal quality, simply remove the FPC cable from the connector on board while
measuring spectrum and look for changes.
- i would for sure check what's wrong with the ext clock input (level too high/low?, rise time to "sharp"?, overshoot?,
how is when AC-coupled?, etc.)
- ...