If it hasn't already been said, the 4ns "jitter" is just the natural result of a 250 MSa/s fixed clock DDS putting out a square wave with a period that is not a multiple of 4ns. Sine waves don't have this jitter, so if you need a clock, try a sine wave.
Does anyone actually have an FY6900 in hand yet? I seriously doubt they've added variable clock or "Magic Pulse" as that would be a major revision and upgrade.
Since no such feature gets a mention in the manual, I'd say your doubts are well founded.
Mind you, when it comes to the output level versus frequency limits specified in
all the manuals for the 6600 and 6800 models, they can't be relied on as accurate sources of such information. As far as sine and square waves go, there's no such 10Vpp limit in the 10 to 20MHz range for either of those models despite what was written in their manuals. The 20Vpp limit runs all the way from DC to 20MHz before dropping straight down to a 5Vpp limit from there onward.
The FY6900 may well do the same, contrary to what is claimed in its manual. If this does prove to be the case, then it may indeed be worthy of consideration provided it isn't burdened with a hefty price premium. Although the 24Vpp spec for DC to 5MHz is more a novelty feature, that and the increase from a +/-10v dc offset to a +/-12v dc offset does strongly imply some sort of PSU upgrade from a (nominal) +/-12v opamp rail supply to a +/-15v rail supply.
Whilst owners of the earlier models (FY6600 and 6800) will see little to no point in purchasing an FY6900 as an 'upgrade', for anyone else contemplating a cheap two channel function generator as an initial purchase for their hobby workbench, the FY6900 would be an obvious choice over its predecessors, assuming it has the same Vpp limits as its predecessors (aside from the 0 to 5MHz 24Vpp upgrade) and is only marginally more pricey.
I notice that they've added a cooling fan to this model. Not so much a 'luxury item' as an essential component that should have been part of the earlier models' features from the start. With the FY6800's mains inlet socket upgrade from the cheap and nasty C8 connector that had afflicted the FY6600 to a C14 connector giving access to a protective earth pin for use as a high resistance "Static Drain" connection to eliminate the half live mains leakage without introducing ground loop issues, that takes care of two of the many modifications that had to be applied to the FY6600,
Although the ground loop issue Feeltech introduced by strapping the BNC shield connections directly to the protective earth still needs a simple resistor mod to correct this mistake, at least the hard work of the original modification needed in the case of the FY6600 has already been done, reducing it to a simple matter of adding a 1 to 10 k resistor to eliminate the ground loop issue and still keep the benefit of half mains live voltage leakage suppression (a 10KR is enough to drop the half mains live leakage potential of circa 110v on a 230v supply to just half a volt).
If they've
finally taken
this opportunity to fix their 86 ohm attenuator pad 'skoolboy howler' by updating the BOM to replace just six smd resistors to correct it to a 50 ohm attenuator, this could well be the icing on the cake that might persuade some FY6600 owners (especially those with a 15, 20 or 30 MHz specced model) to "upgrade". However, if Feeltech stay true to form, this remains an unlikely prospect.
With all of those observations in mind, I can't wait to see what a competently executed review and tear down youtube video will reveal when it is finally released to the market.
[EDIT] After posting this missive, I decided to have a quick look for any FY6900 video reviews on youtube but, as previously, it was blissfully unaware such a device even existed. However, I did come across this interesting reminder as to why these Feeltech offerings are such stonking good value
The Siglent SDG1032X Signal Generator is £360 from their UK agent with the SDG1062X another £80 to get the version that most closely resembles the 60MHz sine wave frequency spec of the FY6600-60M and the FY6800-60M models.
You can compare the specs between the 32 and 62 models here:-
http://www.labtronix.co.uk/drupal/sites/default/files/sdg1000x/SDG1000X_DataSheet_DS0201X_E01A.pdf As for the Rigol DS1022 in that shoot out video, that sucks even more the the Siglent did which fell short in so many ways against the trusty Feeltech products we've all come to know and love/hate.
That shoot out video was such an eye opener as to just how good a bargain these Feeltech signal/function generators actually are, I thought I'd provide a link to it as a reminder to those who nitpick criticise the FY66/68, forgetting completely that even brand named kit with prices that start at a minimum of five times higher have their own shortcomings and limitations which make the Feeltech kit superior in some aspects of their specifications (eg the inability to produce square wave outputs at 20Vpp beyond 5 and 10 MHz for the Rigol and Siglent respectively versus the FY6600 and 6800's 20MHz limits). Mind you, I wasn't impressed by the reviewer's use of a 70MHz BW 'scope and an unterminated BNC cable in his test setup.
The next time you want to nitpick over the irritating use of mcroHertz and milliHertz units in the frequency display (having forgotten that you can cycle through the units on the 6600's rotary encoder's push button function or the 6800's "OK" button), just remind yourself that you've saved yourself at least 280 quid on a "Decent Signal Generator".
If that pleasant thought fails to provide consolation, then you have to ask yourself "Why the f*ck did I waste my money on a "cheap 'n' cheerful" Feeltech generator in the first place?".
Let's face it, the most intractable issue with the FY series of signal generators is their 4ns jitter on pulse and square waves which, quite frankly, are more a cosmetic issue in 'scope traces rather than of any real consequence to a properly designed digital process which should cheerfully take such modest amounts of jitter in its stride.
For Christ's sake, the PC motherboard manufacturers have been offering a 'jitter' function on the clock signals for over a decade now under the label of "Spread Spectrum" taking full advantage of the logic circuits' inherent tolerance to jitter to minimise the impact of any RFI emissions that could otherwise interfere with other users of the radio spectrum.
Obviously, there will be circumstances where this jitter
will be a liability, demanding the spend of another 500 quid or more to run these more demanding test sequences. However, in a hobbyist context, the issue of jitter is less likely to arise. If it does, then the poor hobbyist is simply going to either have to use a cunning work around or else bite the bullet and track down a second hand 'bargain' that
will serve this need.
As a 'heads up', it seems to me that one cunning work around (to save spending 500 quid or more) would be to use the Sinc pulse output to drive a Schmitt triggered input gate or buffer of the appropriate logic family to match what you're testing since, like the sine wave output, this also seems to be free of this 4ns jitter which, unlike the sine wave, offers faster rise and fall times more suited to triggering pulses or square waves with well defined edges.
JBG