@battlecoder
That 4ns jitter in the FY66/6800 AWGs is "by design". However, if you just need a fast pulse with low jitter for a stable triggering source, take a look at the Sinc pulse.
Just like the sine waveform, it's free of this 4ns DAC clock jitter, leaving just the matter of some 300ps Pk-Pk of noise jitter (just over one third of what you see in the SDG1032X AWG
). This is good up to 12MHz (the Nyquist limit for this flavour of Sinc Pulse, 10 squiggles per cycle, being at 12.5MHz).
You don't start seeing the 4ns clock jitter until you go beyond the Nyquist limit. At 20MHz, the 4ns jitter becomes very evident again but if you're after a low jitter pulse waveform around the 10MHz mark, this is your best choice. Not only do you get a low jitter pulse, you also get a very distinctive narrow pulse shape that distinguishes it from the more anonymous sine and square wave shapes making it easy to keep track of the direction of drift at mHz frequency offsets when you might only be glancing at the 'scope trace just once every few minutes.
Of course, you'd only likely to be running such frequency comparisons after upgrading the internal clock reference to a 10MHz OCXO with a 3N502 clock multiplier to recreate the 50MHz clock feed to the FPGA chip.
Incidentally, it's worth keeping in mind that this 4ns DAC clock jitter issue also afflicts massively more expensive DDS based AWGs - it's only the square and pulse waves that get the special low jitter treatment in Siglent's AWG models. Any awfms with a sharp transition suffer this DAC clock jitter effect (6.7ns in the case of the 150MHz clocked DAC in the SDG1000X series and 3.3ns in the case of the 300MHz clocked DAC used in the SDG2000X series to generate awfms),
It came as rather a disappointment to discover that the SDG2000X's Sinc pulse with its 20 squiggles and 300MHz clock whilst looking perfect at its 10MHz 'magic frequency' (exactly 30 clock cycles' worth) turned to shit with just a tiny 1mHz offset. The Nyquist limit in this case being a mere 7.5MHz (and half that for the SDG1000X).
This had only been of importance to me with the FY6600 due to it's excellent low jitter performance as a 10MHz reference signal for testing my DIY GPSDO projects against. It wasn't until rf-loop had given an excellent explanation for this apparent shortcoming of an AWG costing seven times what I'd paid for the FY6600 two years ago and the reliance on the Sinc pulse as an only source of low jitter timing pulse being rendered redundant now that I had a generator that could supply low jitter square and variable duty cycle pulse waveforms up to 25MHz for this task that stopped me from returning it as "Unfit for Purpose".
Now you might think that's the end of the disappointments in the SDG versus the FY AWG comparisons but sadly no. It might surprise you to know that, aside from the crappy dimple operated front panel switches of the FY6600 model range, the FY series has a much more user friendly UI than that of the SDGs which can best be described as "User Hostile".
I know, I know, who would have imagined that, aside from the obvious shortcomings of the FY AWGs, it had so many good features as to outclass the best efforts of Siglent (and naturally, Rigol) and much of the A brand offerings? Who knew? I didn't until I actually got my hands on first an SDG1032X, swiftly followed by the SDG2042X (now hacked to the 120MHz - sine wave only- specification) in my possession.
Obviously, with the SDG2000X series, you get a 16 bit 1.2GSa/s generator (but only 300MSA/s for DDS generated awfms - not a lot better than the FY's 250MSa/s specification) along with a high quality all metal cased construction containing high quality components and a larger feature set (unfortunately cursed by what can only be described as a "Shit UI").
You might wonder then, why I didn't reject this outright as "Unfit for Purpose" but the plain truth is that all of these shortcomings could be sorted by a 4 years long overdue (but quite do-able) firmware update to totally revamp the UI and fix all the other irritations such as polluting a perfectly good lab reference distribution with its rather lacklustre internal 10MHz clock reference whenever it's switched from the external clock back to the internal clock reference.
Simply put, there's a missing user option to disable the "export the internal clock" part of this switching between internal and external clock references. The option to export its internal clock onto a distribution cable can still be useful when no existing lab reference is available to synchronise other test and measuring kit, hence my suggestion to allow the user to configure it to suit their circumstances rather than remove it completely from the clock source choice option.
I had hoped I could retire my much modified FY6600 when I'd acquired the SDG2000X but this hasn't proved to be the case, admittedly largely due to all my modifications to improve its functionality. It still remains a very useful item of test gear in spite of the addition of the generally better Siglent AWG to my stock of T&M kit.
The main annoyance I have with the FY6600's UI is that of the stiff front panel dimple operated pcb mounted switches of rather inconsistent quality making operation of some functions a rather hit and miss affair. I'd speculatively invested some £2.73 in a bag of 100 such switches from Bang Good almost a year ago in the hope I could use them to replace the existing switches and improve the situation but I still haven't gotten around to dismantling the front panel again to verify whether these switches can be used to replace the originals. Assuming the switches do prove to be suitable, there's still no guarantee of gaining a worthwhile improvement.
Ideally, I'd upgrade to the rubber key operated panel switch arrangement as used on the later models but there's no cost effective way to achieve this, hence this rather more pragmatic approach to the problem. A significant factor could simply be due to the plastic dimples themselves which would limit the effectiveness of a switch upgrade. However, I'll be able to get a feel for this (literally!) once I've pulled the front panel apart. Basically, it's a journey into the unknown but, considering the potential payoff, it's a journey I think will be worth embarking upon... when I do eventually get a round tuit.
John
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