Review: Hantek DDS 3X25. Anyone own one?

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Thanks dajones!  Intended to do that to, will put that on my to-do test lists.  Any more ideas, are very welcome.

I confirm dajones posts, there is a persistent jitter of 5-8ns most obvious in the square wave output.  I haven't tried mitigating it, or trying a whole suit of tests, and will post a more detailed review later as I find time.

: /

I was HOPING that it was just 'my unit' that was having this problem.

You might want to take a look at the "Sync-Out" problem.

If I set my unit to 2.5MHz, and display the output signal on one trace, and the Sync-Out on another trace ( on the scope ), I see that
they are in step and not much jitter on the sync line. If I bump this up or down in frequency by a small factor ( 2.51MHz or 2.5000000.001 or 2.4999 )
the Sync-Out signal gets so jittery there doesn't seem to be any timing relationship between the two signals at all.

[alm]

Its a big problem with the Rigol's inherent noise and the potential for artifacts caused by the FFT itself, as we've discussed on eevblog in the past.  Its a reason I'll post scope images more than discuss it [ its also easy to do with the 1052E], you can see the signal vs harmonics+ noise for yourselves.  I also analyzed the maximum amplitude on FFT to see whatever harmonics are there and sometimes, not always, pick up a few distinct frequencies spiking over noise. So far the noise floor and/or specific frequencies are <= 1-5 mVrms for a fundamental at 1.4Vrms.  That's ~ <= 0.36%. 

That would be around -50dB, much better than the specs, but nothing extraordinary for DDS. 0.36% is at the very limit of the 8-bit dynamic range of the Rigol, so I would be suspicious. Setting the vertical scale to dB (assuming the Rigol supports that) would make it easier to see, although it doesn't change the dynamic range obviously. I would also set the sweep speed to a higher setting to get more horizontal resolution on the FFT for looking at the first few harmonics. For more accurate measurements, something like a notch filter might help.

Glad that it appears to perform better than expected, except for the jitter issue. I wonder what kind of change takes place above 2.5MHz, different DAC frequency? 200MS/s and 4kS waveform memory means that the full memory depth can only be used up to 50kHz, so they have to be down sampled above that. Maybe there's some rounding/dithering error there? At 2.5MHz, there will only be 80 points per period, so even minor changes will be significant, especially for something like 2.6MHz, which is not a divisor of 200MHz. Any idea if there's some periodicity to the jitter? If they run the DAC at 200MHz, and alternate periods of 38 and 39, that would generate some jitter.

The manual is useless, as expected (good thing you don't need one), so it provides no clue how it changes the output frequency and what it does with the extra points.

After looking through the manual, I wonder if the arbitrary waveform capability is as bad as it looks? From what I see in the manual, you're forced to edit each individual point individually (if it has more features, it's not mentioned in the manual). I thought the Rigol software was bad, but this seems completely useless. Like Rigol, the compensate for this by leaching on the software that their competitors make available for free. Guess you can't expect them to write their own software for this kind of money.

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Hi Alm,

As always, your posts require a lot of thought for a reply to very insightful points.  A prelim.

The AWG software is crude as you begin with a bitmap image with 1000+ points, moving each point with a mouse will take a long time, so you are right, using some other makers editor is the likely solution, limiting the 3x35's software for touch ups and sending it to hardware.

This Hantek uses Tek and CSV format.  This allows importing other images.  Also, the Rigol exports to CSV so captures can be used too.  I haven't given the AWG component a detailing, so only know these superficially.  I am still characterizing its built in waveforms, but I have tested AWG output and so far so good. 

Clearly, the manual's spec sheet, listed on this thread, is wanting.  But the great news is that the device is performing >= spec sheet, and we are discovering others specs, many are good and less good, i.e., jitter.

I'd bet the "variable" clock design creates more jitter than needed.   But jitter is a weakness in DDS designs for more than just the clock; one reason the Instek 1003 is nice, its more solid a signal reference, none measurable by the Rigol.  It not a problem for design or testing work if your design isn't picky about duty cycles, or operates at speeds under the jitter variation, in this case 8ns or 125 MHz.

http://www.eetindia.co.in/ART_8800549886_1800002_AN_4307fcee.HTM
http://electronicdesign.com/article/communications/jitter-and-its-measurements3781.aspx
http://www.maxim-ic.com/app-notes/index.mvp/id/377

Interestingly, few devices specify jitter, and reading on it more, seems like even the measurement standards are evolving.

Aside, maybe the 'waveform distortion' spec really meant MHz not kHz, because that -50dBc is so coincidental.

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Here's the key component review in pictures.

First pair of images are the Instek 1003 response to its maximum output, basic sine waveform and FFT spectra and next followed by the Hantek sine and spectra.   You can see the absence of any visible harmonics, prior to magnification, to be show later.

Next pair is a square wave from Instek vs Hantek Sq. wave.  CurA marks the 17th harmonic, at 51MHz, and CurB marks the location of a large spurious harmonic, visible with magnification, on the noise floor.

The noise floor of sine wave magnified  including a spurious high frequency component.  2.48mV/1Vrms gives the noise ~ 0.248%.  The spurious high frequency is about 12mV or 1.2%, its ~ at 250MHz.

The jitter close up, at 5.20ns.

Hantek's maximum frequency at 75 MHz sine, with FFT spectra, clean at 75 MHz, with the Rigol at highest gain, and image stabilized with averaging [I use a 1052E unmodded, bandwidth of 50 MHz.]

Sample AM modulation.

Magnified noise floor on FFT at 40 MHz sine, from the Hantek.  Note the 5mVrms spike at 458 MHz, CurB.

Sample of my AWG output, a sine wave with negative and positive voltage spikes, and its spectra.

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Sample FM Modulation image.

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Comments on bolded items:

Yep, the harmonics are measurable to the limits of the Rigol's capacity.  So at worse the Hantek is doing in the neighborhood of no more than 0.4%, about the 1/8 bit resolution of the Rigol.  I looked at the distribution in dB too, but converted I can't go below~ -50dB.  I also swept the timebase from end to end, looking for trouble.  I checked views with all the various FFT windows: Hanning, Hamming, Blackman, to get the best view.  The pics are just representative of the best and worst.

Although the jitter is there, I think its effect is a bit overemphasized, it only matters when circuits are sensitive or nearer the jitter's frequency, such as using it to clock a ADC.  Since it appears fixed, it becomes more rate limiting at high frequencies, at 2.5 MHz the jitter represents 5ns/400ns a 1.25% variation in say, the duty cycle of a square wave clock.  But at 25 MHz, its 12.5%.  Can't hurt when used as a signal generator for input emulation knowing this restriction.

Formally, its effect can be thus:



It can drive an ADC ~ 100kHz before the noise begins to rise above the ENOB limits of 50dB.

http://www.analog-europe.com/en/understanding-ac-behaviors-of-high-speed-adcs.html?cmp_id=71&news_id=222901444&vID=35


I think the jitter is a pickup of the maximum clock frequency, 5ns ~ 200MHz, as the manual states, its just an educated guess.  Being the maximum DAC clock speed, the Nyquist frequency is 100 MHz, so that's the ceiling on waveform generation.

There does seem to be periodicity to the jitter, if you switch the acquisition mode to 'average' the jitter completely disappears, so its appearing at a fixed interval, like its frequency modulating the clock period.  

Yes, the manual is very superficial.  There is no access to adjusting the clock period directly.  As you pointed out before, the software has a demo mode, why they didn't make it available for download for promotion purposes is curious, but methinks they were afraid of criticism of its dullness and thus, kill 3x25 sales.

Your AWG comments spurred me to examine it in detail.  When selected, it takes the existing waveform on the screen, be it sine, sq, ramp etc., and enters editor mode.  You can thus, mess up the waveform easily, as in the photo I left of a sine wave with spikes on it.

I'll report on uploading a CSV file later.

That would be around -50dB, much better than the specs, but nothing extraordinary for DDS. 0.36% is at the very limit of the 8-bit dynamic range of the Rigol, so I would be suspicious. Setting the vertical scale to dB (assuming the Rigol supports that) would make it easier to see, although it doesn't change the dynamic range obviously. I would also set the sweep speed to a higher setting to get more horizontal resolution on the FFT for looking at the first few harmonics. For more accurate measurements, something like a notch filter might help.

Glad that it appears to perform better than expected, except for the jitter issue. I wonder what kind of change takes place above 2.5MHz, different DAC frequency? 200MS/s and 4kS waveform memory means that the full memory depth can only be used up to 50kHz, so they have to be down sampled above that. Maybe there's some rounding/dithering error there? At 2.5MHz, there will only be 80 points per period, so even minor changes will be significant, especially for something like 2.6MHz, which is not a divisor of 200MHz. Any idea if there's some periodicity to the jitter? If they run the DAC at 200MHz, and alternate periods of 38 and 39, that would generate some jitter.

The manual is useless, as expected (good thing you don't need one), so it provides no clue how it changes the output frequency and what it does with the extra points.

After looking through the manual, I wonder if the arbitrary waveform capability is as bad as it looks? From what I see in the manual, you're forced to edit each individual point individually (if it has more features, it's not mentioned in the manual). I thought the Rigol software was bad, but this seems completely useless. Like Rigol, the compensate for this by leaching on the software that their competitors make available for free. Guess you can't expect them to write their own software for this kind of money.

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More tests of the Hantek.

The first image is a small clock output pickup from the sync output.  This contamination could be the source of the jitter.

The next 2 are simulated RC discharge outputs.

AWG:

The Hantek wave drawing software has very few timsaving options but as is, its very useful.  Its as easy as drawing with a mouse; its better with a pen stylus.  Users need to save work as soon as done, because if another waveform is selected by error, the drawn waveform is deleted without warning.

I imported Rigol 1052E waveforms into the Hantek.  The CSV files are not drop in compatible.  To get the correct format, save any Hantek CSV waveform, open it and overwrite its data points with the datapoints of the Rigol, just insure data is on the same scale and format, which can be done easily with Excel to format a column's properties.

Hantek cannot import wfm files saved by the Rigol.  I'll report if externally generated wfm files can be converted to CSV without incompatibilities.

That said, the Hantek can generate complex waves, but the AWG output is limited to 100kHz tops. depends on the complexity of the Arb and the MCU capacity to output it fast enough to meet the frequency you enter.

Below are samples of simulated cardiac waveforms I drew, these are typically complicated after heart attack types, which requires good frequency response to reproduce.

The first show a realistic rate of 60 Hz, or beats per minute, using the Rigol 1052E roll mode for sweep.

The same cardiac waveform running at 100kHz and 10kHz, all without noticeable distortion.

Other AWG output:

Noise burst detail, zoomed in from a single pulse.  These were captured at 1Gs/s at 10us and zoomed in to 1us.
Noise burst, as a pulse at 10us.  

Finally, a complex waveform, mix analog digital with various levels.  

The complex waveforms are challenge to get the 1052E to sync properly, but it did with with rock stable accuracy with manual tweaking.

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You're welcome.  Shafri, maybe this thread has to be moved to reviews, as it began as an inquiry, but it became a review.

I'll rewrite the specs into a table format so its summarized.  Although I have a few more tests to run, frequency stability being one, I think based on what is posted to date, I could summarize it:

The Hantek DDS 3x25 is a solid function generator with arbitrary waveform capability, far better in performance than most analog function generators, in its price range or with similar specifications.  It one of the lowest cost 25 MHz capable DDS function generator on the market, and likely the only one with AWG capability.

The 3x25 is down -3dB at 25 MHz, but is usable to 75 MHz, at -12dB, for sine wave only, with the same distortion+ noise limits.


It can be found typically for $150, but Saelig still has it for $100, +10 s/h.  Its a sleeper, so it can be found for a steal.

good work!

[saturation]

I've completed frequency accuracy and stability measurements using a 4ppm B&K 1870 frequency counter.  Conditions: 70F, 25% RH, ~ 1025 mBar.

Specs of the test equipment:

http://www.bkprecision.com/products/model/1870/handheld-frequency-counter-12ghz.html


Hantek Tests:

After 24 hours stability is 2.00 ppm.  1 hour stability is 0.60 ppm.

Accuracy against the B&K, rated at 18.01 <= 200 ppm.

This is better than specifications mentioned in the manual, and stable for ~ 24 hours.

[DaJones]

The Hantek DDS 3x25 is a solid function generator with arbitrary waveform capability, far better in performance than most analog function generators, in its price range or with similar specifications.  It one of the lowest cost 25 MHz capable DDS function generator on the market, and likely the only one with AWG capability.

Man, I don't understand how you can say that!

The thing glitches like crazy for square waves above 2.5mhz ( except a few stable spots like 10mhz ).

The sync out line has no timing relationship to the output signal except at those rare "stable" spots.

The sync out line glitches every 20us ( 50khz ) and will glitch any output waveform other than sine waves.

I could NEVER recommend this to anyone, except maybe as a source of sine waves, and as long as you
didn't need to use the sync out line at all.

If you did your stability test at one of the "stable" spots ( like 10mhz ) you might want to try it again at 10.1mhz.

[saturation]

Hi dajones:

I'd glad you brought that up.

You are correct, the sync output is adequate to about 1MHz, then its heavily distorted, and the signal is increasingly useless; I can analyze stable waveforms with various combo of the Rigol's trigger options to about 3 MHz but its easier to just trigger on the channel signal, and the output is very stable to 75 MHz on sine at -12dB and ~ 25 MHz most everything else, at -3dB output.

For others interested, I did not test the pattern generator and digital output.  The input trigger works as expected.  Hantek allows you to adjust the phase angle of the output 0-360 degrees and there is a DC voltage offset.  Note, the output is LVCMOS, and swings only 3.5Vpp.  What I've done in the past is use a non-inverting opamp at the output stage with sufficient gain-bandwidth product for the needed frequency, you can optionally use the phase angle to adjust for any shifts caused by the amp.

I weighed all the pros and cons, and for me the pros win out.  But your need may differ, particularly if you need the sync signal output, its not good.  I'll add scope grabs when I've time.  

I gave it good marks because I don't think you can find a variable sine wave source for 75 MHz for $150, or even Seilig's $100, much less the typical functions of an analog, not DDS, function generator for that price.  The output is very stable, but the jitter is a problem in certain designs requiring strict duty cycles.

Most $150-200 FG output ~ 3MHz, albeit they may have clean signals through the bands, analog FG suffer from frequency variations, between 0.1-1.0% / hr even when already at operating temps.  Of top analog FG brands, many are more stable, but far most costly, and no where in ppm stability.  Likewise, the harmonic content is very variable too.

http://www.eevblog.com/2009/04/24/eevblog-5-instek-function-generator-review/

The DDS variants change the field for FG, but the starting price for >3 MHz is at least 2-3x the cost of the Hantek.

If you have a good FG to recommend with stable clean outputs, link them here.  One recent post was a surprise, the Velleman.  But again, its under 3 MHz:

https://www.eevblog.com/forum/index.php?topic=1869.msg31157#msg31157

Its one reason I posted my raw screens, so you can decide for yourselves its value, its the equivalent of a revised spec sheet.

I'll post my scopes images of the issues you raised later on.

The Hantek DDS 3x25 is a solid function generator with arbitrary waveform capability, far better in performance than most analog function generators, in its price range or with similar specifications.  It one of the lowest cost 25 MHz capable DDS function generator on the market, and likely the only one with AWG capability.

Man, I don't understand how you can say that!

The thing glitches like crazy for square waves above 2.5mhz ( except a few stable spots like 10mhz ).

The sync out line has no timing relationship to the output signal except at those rare "stable" spots.

The sync out line glitches every 20us ( 50khz ) and will glitch any output waveform other than sine waves.

I could NEVER recommend this to anyone, except maybe as a source of sine waves, and as long as you
didn't need to use the sync out line at all.

If you did your stability test at one of the "stable" spots ( like 10mhz ) you might want to try it again at 10.1mhz.

[Mechatrommer]

Just noticed this tonight (no affiliation) on clearance for $99USD:
http://www.saelig.com/CL/CL001.htm
Not sure if this means they are discontinuing them...

its discontinued, not sold anymore. maybe i was thinking too long, gotta find another source or any info on the newer product?

this thread is perused:
1) sine wave: 1.5Vrms?@3MHz, 0.2Vrms?@75MHz? is it enough/good as an external clock for an mcu? or for mcu work?
2) arbitrary good to 100kHz only? or can be more? like 1-3MHz is possible?
3) what is "sync output" for?

my fingers are tinggling, should i hit the $150 3x25?

[saturation]

Hi Safri,

Its at least sold out by Seilig, you still have many eBay sellers and other vendors in Asia, there are many out there I see on google, find one close to you in Malaysia.

I wouldn't be surprised if the item is discontinued by Hantek, it might be why its so cheap; it was designed with bugs in it that isn't worth repairing or recalling; that's why I think its a steal, the parts of it that work well provide what I reviewed here.

To answer your questions:

1. 3.5Vpp is ~ 2.5Vac rms.  -12 dB for 2.5Vac rms = 0.63Vac rms.  I'm not so sure -12dB is the Hantek roll off or my Rigol's.  I'll recheck and post a correction if I can confirm its source.

The clock output is stable to 3MHz.  As you go faster, that jitter will eventually cause inconsistent clocking, but when that happens depends on your circuit.

It is possibly good enough for non-LV CMOS circuits, because the maximum output of 3.5Vdc can be made by adjusting the voltage offset and is above the switching level of TTL and CMOS.

2. Arbitrary depends on how bizarre your waveform, I can get many stable waveforms over 3 MHz, and easily under 100kHz, but its best to monitor the output on your scope as you ramp the frequency up. That's because waveforms beyond just sine requires more frequency response from the hardware.

3.  

Sync output sends a logic level output that's the same frequency as the output signal.  

You can use it as an alternate trigger signal for a scope, if none of the scope's options work.
You can synchronize multiple devices to output simultaneously.  For example, you can cascade multiple signal sources together than have trigger Input and Sync output, taking the sync output of one device to the trigger input of another, and daisy chain multiple devices, to simulate multiple simultaneous synchronized inputs to your design.  This is not as straightforward as it sounds, because as you daisy chain these devices, there is always some trigger input delay so you need to manually adjust the phase shift on each device as the sync signal propagates down the line of signal sources.

Because the sync out of the 3x25 is unreliable, you can't daisy chain 3x25s, but you can trigger it. Also, if you need the sync signal for any other reason, it doesn't work past 1MHz.

Just noticed this tonight (no affiliation) on clearance for $99USD:
http://www.saelig.com/CL/CL001.htm
Not sure if this means they are discontinuing them...

its discontinued, not sold anymore. maybe i was thinking too long, gotta find another source or any info on the newer product?

this thread is perused:
1) sine wave: 1.5Vrms?@3MHz, 0.2Vrms?@75MHz? is it enough/good as an external clock for an mcu? or for mcu work?
2) arbitrary good to 100kHz only? or can be more? like 1-3MHz is possible?
3) what is "sync output" for?

my fingers are tinggling, should i hit the $150 3x25?

[Mechatrommer]

yes its still available in ebay. and the bugs, dajones tried to highlight that clearly. but as you said, and i think, a 75MHz sine is a hard thing to find at the price, the DDS-3005 cost more than twice and no indication it can do 75MHz sine. as for other signal than sine (square, arb), i will treat them as extra features of the generator, so slower frequency should be acceptable for me, in fact imo 3MHz is pretty good already. but the 3x25's -12db concerns me, as your pictures indicate, its around 384mVpp @ 75MHz sine. so i'm rounding it to roughly 0.2Vrms, i was quoting Vdc (Vac/2 to my understanding, sorry if i'm wrong), but whatever! your pictures worth 1K words.

my only concern if its possible feeding the signal into the mcu clock and get the mcu MIPS'ping, you know what i mean? running. as jitter is concerned, perharps that related to how accurate the timing is? so far i dont think i will need a very accurate timing/clocking project, if i do maybe i should get more stable oscillator for the project. i just want to know what happen if the mcu is running at its highest speed (say if a PIC can run at max 40MHz, then i can tune the hantek to 40MHz sine and feed it to the PIC), thats all that i can imagine so far. or is it do i need an extra amplifying circuitry before fedding to mcu? i dont know, maybe i'm too newbie on this and have to make some study. you mentioned about "voltage offset" which is not very clear to me, but dont bother, i'll go figure that out. so the answer to my concern should be just as simple as "yes" and "no".

other than that, i would like to experiment with LCR meter as you've suggested in another thread, and other possibility within the reach of the generator. pretty much thats all. i'm not that complicated beast . OR just maybe this whole thing is just a delusion to me?

ps:
comparison between 3005 and 3x25 (html)
3005 manual (pdf)
3x25 manual (pdf)

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Yes, it is.  You are correct, its down ~ 384mV at 75MHz, but its still clean, harmonic free as I can measure  

You can easily amplify it for more gain using a op amp rated for that speed, made as a non-inverting amplifier, the chips are ~ $5.  For such high frequencies use dead bug style wide ground plane construction.  You can then control the output as you did before but with much higher output.

http://www.analog.com/en/amplifiers-and-comparators/operational-amplifiers-op-amps/ad8011/products/product.html

Yes, the Hantek 3005 cannot do 75 MHz, very few function generators can.  At 20 MHz, they run in the $400, of course, unlike the 3x25, all outputs work    Even second hand eBay RF sources cost more and not as stable.

I do not know if driving an MCU clock with the 3x25 will create issues because of the jitter, jitter becomes a problem the higher the clock speed is, so it depends how high you ramp up the clock speed.

If I need a good clean output, I use the Instek 1003, its the reason I bought it, and then the 3x35 is mostly as a signal source.

I do intend to use the sine wave as my highest output clock source, as you suggest.  A simple way to convert sine to square is simply clip the sine wave peaks:



Or use a Schmitt trigger, and adjust the threshold trigger voltage to vary the duty cycle .  This design just reuses the op amp you already have, so get several if you intend to do something like this [this example uses the 741 op amp, but op amps in general use the same design layout].

yes its still available in ebay. and the bugs, dajones tried to highlight that clearly. but as you said, and i think, a 75MHz sine is a hard thing to find at the price, the DDS-3005 cost more than twice and no indication it can do 75MHz sine. as for other signal than sine (square, arb), i will treat them as extra features of the generator, so slower frequency should be acceptable for me, in fact imo 3MHz is pretty good already. but the 3x25's -12db concerns me, as your pictures indicate, its around 384mVpp @ 75MHz sine. so i'm rounding it to roughly 0.2Vrms, i was quoting Vdc (Vac/2 to my understanding, sorry if i'm wrong), but whatever! your pictures worth 1K words.

my only concern if its possible feeding the signal into the mcu clock and get the mcu MIPS'ping, you know what i mean? running. as jitter is concerned, perharps that related to how accurate the timing is? so far i dont think i will need a very accurate timing/clocking project, if i do maybe i should get more stable oscillator for the project. i just want to know what happen if the mcu is running at its highest speed (say if a PIC can run at max 40MHz, then i can tune the hantek to 40MHz sine and feed it to the PIC), thats all that i can imagine so far. or is it do i need an extra amplifying circuitry before fedding to mcu? i dont know, maybe i'm too newbie on this and have to make some study. you mentioned about "voltage offset" which is not very clear to me, but dont bother, i'll go figure that out. so the answer to my concern should be just as simple as "yes" and "no".

other than that, i would like to experiment with LCR meter as you've suggested in another thread, and other possibility within the reach of the generator. pretty much thats all. i'm not that complicated beast . OR just maybe this whole thing is just a delusion to me?

ps:
comparison between 3005 and 3x25 (html)
3005 manual (pdf)
3x25 manual (pdf)

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3 more 1052E grabs.

-3dB mark is likely for the Hantek, 32 MHz.  White is at 0dB for comparison, see photos below.  I think this is correct because the 1052E is rated to ~ 50 MHz, which is its -3dB mark, and this response is consistent with the tested rise times, blue is from a test signal from the Instek 1003, yellow is the rise time of the Hantek:



The slower Hantek gives ~ bandwidth of 0.35/15.5ns ~ 22.6 MHz.
The faster Instek gives ~ bandwidth of 0.35/4.8nS ~ 72.9 MHz.  

The above suggests the Rigol is much faster the Hantek, so the roll off is most likely caused by the Hantek.

Other 2 photos below are:

Sine output and sync output, in sync up to 2.5 MHz.

Unstable sync output at 2.8 MHz.  Using persistent view to show instability.

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dajones initially reported about the inability of the 3X25 to provide a suitable sync signal, that I confirmed.

The manual states the output port is capable of ~ 50mA, at 3.5v.  That suggests it was designed for an impedance of ~ 70 ohms.  I measured the sync output port at nearly 50mA too.  

Thus, all you need do is terminate the sync output at 50 ohms, and you have a usable sync signal good to 25 MHz.  I've confirmed this.

I have not solved the jitter issue, its still there.

Yellow is the signal output, blue is the sync signal.



At 25 MHz, there is at least a 45 marked phase shift.  But a stable image can be made by adjusting trigger level.



So fairly small excursions can be sync'd, here's 8mVpp, the limits of the 3x25 before severe pixelation begins.

[alm]

The manual states the output port is capable of ~ 50mA, at 3.5v.  That suggests it was designed for an impedance of ~ 70 ohms.

My guess is that it's 50 ohm, like 95% of the generators. Should be easy to find out by measuring open circuit voltage and short-circuit current.

Thus, all you need do is terminate the sync output at 50 ohms, and you have a usable sync signal good to 25 MHz.  I've confirmed this.

Good find. Most generators are happier with a 50ohm load, unless otherwise specified. I expect the distortion and flatness spec were also specified for a terminated load. If you're unable to do this, back termination (termination at the generator's end) is usually preferable to none at all.

[saturation]

Hi alm, yes absolutely, just an estimate but it confirms the 3x25 provides enough mW to drive a low impedance load [ 3.5Vp ~ 2.5V rms, @ 50mA gives 50 ohms].  The manual does not say the sync output was too, but why not?  And I presume now the trigger input is 50 ohms too, and duh, I've been using it already driving it from the 50 ohm Instek 1003.  And yes, did so measure the output current.  Yes, reconfirmed voltage output for flatnes but only on select frequencies before its roll off.

Here are some additional images regarding the sync and signal stability.  I think they show the phase shift better and the solid Lissajou image demonstrates the overall stability between the 2 signals.

Blue = sync output

Yellow = output signal

The manual states the output port is capable of ~ 50mA, at 3.5v.  That suggests it was designed for an impedance of ~ 70 ohms.

My guess is that it's 50 ohm, like 95% of the generators. Should be easy to find out by measuring open circuit voltage and short-circuit current.

Thus, all you need do is terminate the sync output at 50 ohms, and you have a usable sync signal good to 25 MHz.  I've confirmed this.

Good find. Most generators are happier with a 50ohm load, unless otherwise specified. I expect the distortion and flatness spec were also specified for a terminated load. If you're unable to do this, back termination (termination at the generator's end) is usually preferable to none at all.

[Mechatrommer]

damned! i just hit it, buy it now from ebay chinese seller. wish me luck.

[saturation]

Please add your review when you get it! 

damned! i just hit it, buy it now from ebay chinese seller. wish me luck.

[Mechatrommer]

Please add your review when you get it! 

i dont think i can do any better than yours. and i'm not in rush, just want to make early preparation before i can start any project. maybe i will just have a rough look when the thing arrives. and to see if there is any prospect from pc programmability point of view. i hope i'll come out with something

[frogblender]

I took delivery of a DDS-3x25 a week ago.  After 1 hours of fiddling:

- Same ±5.5nS jitter on square waves as others have noted above.
- Sine wave generation seems OK.  Above 30 or 40Mhz it starts to become visibly distorted, but not horribly so.
- I haven't messed with sync out
- Software is not very good (me=Win7-32pro)
    - virtual frequency adjust knob (on the screen), when turned by the mouse, changes freq in ONE Hz increments - Useless above 100Hz.
    - many options grayed-out in the software, reason unknown.  Can't sweep.


I also bought a Hantek DSO5202B 200MHz scope, which is not bad at all for the price.  Although this is off-topic, I had a wild dream about using the generator and scope together as a Network analyzer (would give me a nice graph of amplitude and phase response as a function of freq for my device-under-test) - anyone have any ideas how to do this?   I also have this scope-and-generator-in-one:

http://syscompdesign.com/CGR101.html

which produces beautiful bode plots - but only up to 2MHz - I need something up to 10MHz.  Any ideas?

[saturation]

LARGE Hi res PCB photos are here, I did not take them, just found it by accident:

http://biot.com/p/

Small versions as teasers

[saturation]

Good you brought these up:

I don't have the unit at hand, but I recall the knob can be spun fairly quickly.  BUT, you'll find that is uses only the first 5th or 6th most significant digits, but software will allow you adjust in any position before it, and thus, will not result in any output.

Options are greyed out until you select the mode, then only the appropriate menu appears.  For example, until you select square waves, the subfunctions for square waves are not available, such as adjusting duty cycle.  The same thing for sweeping for AM and FM.

You can use a signal source and a scope in the X-Y mode of the scope, and evaluate Lissajou patterns.  It will provide  phase, amplitude and frequency relationship between 2 channels.

One advantage of USB scopes is that the raw data can be imported into software for presentation in any format, such as Bode plots. But if you were trying to test your hardware for its frequency and phase response for practical reasons, you now have basic tools to make that assessment.  For example, the syscomp image would appear as a very squashed line at 12kHz in phase, then a turn to equal proportions at X=Y amplitude, and begin to move from a circle to an ellipse as the phase shifted.

http://en.wikipedia.org/wiki/Lissajou#Practical_application

I took delivery of a DDS-3x25 a week ago.  After 1 hours of fiddling:

- Same ±5.5nS jitter on square waves as others have noted above.
- Sine wave generation seems OK.  Above 30 or 40Mhz it starts to become visibly distorted, but not horribly so.
- I haven't messed with sync out
- Software is not very good (me=Win7-32pro)
    - virtual frequency adjust knob (on the screen), when turned by the mouse, changes freq in ONE Hz increments - Useless above 100Hz.
    - many options grayed-out in the software, reason unknown.  Can't sweep.


I also bought a Hantek DSO5202B 200MHz scope, which is not bad at all for the price.  Although this is off-topic, I had a wild dream about using the generator and scope together as a Network analyzer (would give me a nice graph of amplitude and phase response as a function of freq for my device-under-test) - anyone have any ideas how to do this?   I also have this scope-and-generator-in-one:

http://syscompdesign.com/CGR101.html

which produces beautiful bode plots - but only up to 2MHz - I need something up to 10MHz.  Any ideas?