SeeSii branded JDS6600

[BassClef]

I just received a SeeSii-branded JDS6600 60 MHz signal generator. I'm not an EE, I'm a ham radio operator. I mostly fix, align and adjust things in the 3-30 MHz range. I've lusted after the Siglent SDG1032X, but couldn't justify the cost vs. the amount of use I'd actually get from it. The Uni-T UTG932E was also tempting, but I was put off by the current U.S. cost and the spurs issues mentioned here. The FY6800 and 6900 are hard to find and seem overpriced, and many here complain about power supply issues.

Here are a few observations for anyone considering this model.

I ended up with a SeeSii-branded JDS6600 that they call a "DDS 60M" for $125. I used Amazon, as I'm generally not comfortable buying directly from China. The price fluctuates daily. SeeSii claims their unit is "improved," and the manual claims 266 megasamples/sec, rather than the traditional 200. Who knows? One very nice surprise was that the dreaded 50+ volts AC on the BNC shells was not an issue. I measured about 6 VAC with the supplied wall wart and 9 VAC with a Radio Shack 3-5-6-7-9-12V 2.5A variable wall wart. The Radio Shack supply shows a bit less noise on my scope, so I may use that until I find a linear PS.

One disappointment was that the SeeSii unit does not do AM modulation. I thought it did, but evidently I confused a FeelTek FY6600 review with a review of the JDS6600. That might not matter, as I also have a TinySA, which does AM and FM throughout its range. Crudely--the modulating waveform is a few stairsteps, rather than a smooth curve. But it works.

Questions and a photo follow...

[BassClef]

So... Question #1:  Is there any way to get the this unit to do AM, or some audible facsimile of it, perhaps using the waveform creation software? I saw a video where some reviewer claimed he could do it. It involved copying a sine wave at a carrier frequency over a couple of dozen cycles, then entering a modulating sine wave and multiplying them together. I'm skeptical about the numbers involved, because I don't quite see how enough of an AF signal 300 Hz-1 kHZ could be adequately superimposed on only a couple of dozen RF waves, thousands to millions of times faster.  Am I missing something?

Question #2:  I've noticed that at some combinations of frequencies and amplitudes, the sine waves output displayed on my scope (Siglent 1202X-E) will "lean" forward slightly. Or there will be a slight flattening of one side of the peak, sometimes the rising side, sometimes the falling side. The attached photo shows both (precarious balance only so I could get both devices in the picture!).

Sometimes the wave shape looks perfect except for slightly thicker peaks with tiny flashing dots in the thicker areas. All this happens on either channel of the scope or the SeeSii, and with several different BNC-to-BNC cables.  Is this anything to be concerned about, or do all these inexpensive units do this to some extent due to aliasing, rounding errors, baubling, etc.?

[Bud]

You will likely be getting more waveform distortion as you go closer to the upper frequency limit. DDS generators inherently have images in the spectrum so a good filter needs to be present on the output. Knowing poor RF design practices of the country of origin of your device I am sure the antialiasing filter is cheap and simplistic, that is why you see the distortion.

[BassClef]

I'm returning SeeSii's purportedly "upgraded" JDS6600. I really want AM and FM modulation. I found a used FY6800 (KKMoon branded) for $94, which just arrived. It works great except for an occasional glitch in the rotary encoder dial. I like the 6800 and I'm keeping it.

The two devices display some interesting differences between some of the waveforms. Once you get above a couple of MHz, square waves are not very pretty on either device, even if they are usable. What really caught my eye was that apparently, on the SeeSii, the waveforms were tweaked to minimize overshoot and ringing at the top of the positive upswing and the bottom of the negative downswing. They also don't display the dreaded 4 ns jitter "echos" on rising and descending parts of the square wave. Conversely, sine waves on the 6800 look better. Some sine waves on the SeeSii are slightly "punched in" just before the peak, or "lean" forward (see my previous post in this thread). It's almost as if someone tweaked things to improve the square waves, which negatively affected the sines.

I also measured the AC noise envelopes of the two devices. The width of the ambient noise envelope in my "shack" measures between 6.9 and 7.6 mV on my scope. With power applied, the SeeSii JDS6600, powered by my lowest noise wall wart, has a noise envelope of 8.36 mV. The FY6800 has 9.44 mV.  I think I can live with 1.1 mV extra noise.

[radiolistener]

One disappointment was that the SeeSii unit does not do AM modulation. I thought it did, but evidently I confused a FeelTek FY6600 review with a review of the JDS6600. That might not matter, as I also have a TinySA, which does AM and FM throughout its range. Crudely--the modulating waveform is a few stairsteps, rather than a smooth curve. But it works.

All FPGA based Chinese AWG have bad modulation implementation.
Not because it is impossible, it just happens that they implemented it with mistakes...

SeeSii claims their unit is "improved," and the manual claims 266 megasamples/sec, rather than the traditional 200. Who knows?

DAC904 max sample rate is 165 MS/sec. If they claim 266 MS/sec, they probably replaced DAC chip with R2R DAC on discrete components. It means that it's performance will be much worse than with DAC904 and dynamic range will be limited with about 40 dB. Because discrete R2R doesn't allow to get good linearity due to random delay for each data bit.

So, it's better to get AWG with overclocked DAC904 running at 200 MHz, than discrete R2R DAC running at 266 MHz.

[Wil_Bloodworth]

Are you still happy with the KKMoon FY6800?  I see they now have an FY6900 for ~$88 and am thinking of picking it up for the same reason you did.

Thank you,

- Wil

[DaneLaw]

Only got a Feeltech FY6900/60Mhz as dedicated arb DDS signal gen, with the price that Banggood was selling/clearing them at in their EU warehouse (75US delivered) in the first half of 2020.. it's been solid so far (+3years).. Do like that I can run it from USB, like on the scope's USB-out or power bank, or if you control it with a laptop/PC it will power from that single USB dateline..
Been wondering about dropping a battery in my unit.
FY6900 does have a shutload of signals, & outputs (7 BNC + a 4ch. TTL out/8pin) and around 65 programable arb waveforms that one can fiddle with in their PC software - with the price in mind - it's been hard to beat the last 3 to 5 years.

- if it's still a decent "buy" in late 2023 versus alternatives..I don't know, as other cheap budget signal gens have arrived from the likes of UnitT, Owon, and others, with even bigger screens and what looks like a more optimized interface, with a num-dial and all that pleasant jazz.

One disappointment was that the SeeSii unit does not do AM modulation. I thought it did, but evidently, I confused a FeelTek FY6600 review with a review of the JDS6600. That might not matter, as I also have a TinySA, which does AM and FM throughout its range.Crudely --the modulating waveform is a few stairsteps, rather than a smooth curve. But it works.

Yes, the TinySA does a very crude AM modulation, I recall it's merely 8 interpolation points on the basic TinySA-unit, while the TinySA-Ultra takes it up a notch to 128 points, so a lot cleaner.. the TinySA Ultra works surprisingly well as a handheld basic signal gen for the things it does, though its amplitude is far from linear when you get up in the higher end of its Ghz-span, - but that goes without saying, would be a threat if its secondary feature (signal out) did 0hz to 4.4/5.4Ghz with -123dbm to -18dbm level control with full linearity - but a good part up its signal-out-span, it performed quite well, according to my RF power meters.

The FY6900 modulation is another fish

Example with TinySA Ultra modulation..