The Siglent SDG2042X Thread

[ton4eff]

I tried with different trigger frequencies and every single option available, but it behaves the same. The problem is in my SDG2042X generator not a trigger problem with the scope, because with my other generator there is no such a problem with exactly the same settings.  And you can actually hear the sound from the receiver becoming different when I switch to external trigger.

[ebastler]

I tried with different trigger frequencies and every single available option available, but it behaves the same. The problem is in my SDG2042X generator not a trigger problem with the scope, because with my other generator there is no such a problem with exactly the same settings.  And you can actually hear the sound from the receiver becoming different when I switch to external trigger.

You misunderstood, I am not claiming it is a scope problem. I actually tried this before I posted: When I set 14.0 ms sweep duration on the SDG2042X and 14.1 ms period of the external trigger, the SDG produces stable sweeps. When I set 14.0 ms period of the external trigger signal (or less), the sweep becomes intermittent.

Edit: Fixed the sentence above...

[tautech]

But when I try to trigger from external source, the signal starts to disappear and it doesn't work as it should anymore. I tried 2 different external generators as a trigger source and the result was the same. Of course the external trigger signal is with the same amplitude and frequency as the internal one. Any ideas how to fix this?

Q.
Are you meeting the Trigger Input spec as specified on P10 in the datasheet ?
https://int.siglent.com/u_file/download/22_07_28/SDG2000X_DataSheet_DS0202X-E02G.pdf

[ton4eff]

@ebastler Yes, 14.1ms trick works, thanks for the tip, also with 7.1ms for example! I'm using 14ms, because my scope has 14 horizontal divisions and this way I know that the sweep is centered exactly around the span. I'll try to investigate further this issue, because I think that this is not a solution, but only passing around the real problem. Or I'll just have to try to live with this... 
@tautech, I think yes AFAIK, I did try with different signal levels (TTL and CMOS). Also tried to change the offset, phase etc... No luck.

[ebastler]

@ton4eff, glad to hear that this works. I don't think what you are encountering is a bug -- you could call it a question of design philosophy:

You have defined in the SDG that a complete frequency sweep takes 14.0 ms. So what should the function generator do if a new trigger edge arrives while the sweep is still in progress? Maybe your Rigol DG1022Z is designed to abandon the current sweep early and start a new one. The SDG seems designed to complete the current sweep and ignore that premature trigger.

The solution seems easy and quite clean: Just set the sweep duration slightly shorter than the trigger period. If for whichever reason your trigger period needs to be 14.000 ms, just set the sweep duration in the SDG to 13.999 ms.

[ton4eff]

@ebastler, Thank you for your time! My knowledge with these units is limited, I have to admit... But allow me to disagree. If it's a design philosophy, why it's working with the internal trigger source properly? I particularly and thoroughly compared the external trigger sources with the internally generated signals and made them exactly equal. One is my Rigol DG1022Z and the other is old but very trusty HP3325A. 

[ebastler]

If it's a design philosophy, why it's working with the internal trigger source properly?

Because the internal trigger source automatically re-triggers right after the sweep has completed. Not (significantly) later, and certainly not sooner.

With automatic internal retriggering,  there is no independent timing source for the trigger period. It is directly derived from the sweep period in this case and always exactly in sync.  So there can be no missed triggers.

I particularly and thoroughly compared the external trigger sources with the internally generated signals and made them exactly equal. One is my Rigol DG1022Z and the other is old but very trusty HP3325A.

But making them "exactly equal" is the problem! You have created a "race condition": You try to ensure that the next trigger comes at exactly the same time when the sweep has been completed. But if the trigger arrives only a few µs earlier, the SDG will ignore it. So a little bit of jitter in the trigger period may cause some triggers to be missed randomly. Or a trigger period which is a few µs too short will systematically cause every other trigger to be missed.

You might have a bit of a mental block here. Maybe give it a rest for now, sleep on it and revisit the question with a fresh mind tomorrow.

Edit: Typos. I should probably also take a break...

[ton4eff]

You might have a bit of a mental block here. Maybe give it a rest for now, sleep on it and revisit the question with a fresh mind tomorrow.

OK, that's a good advise, I'll take it... 

[mawyatt]

If it's a design philosophy, why it's working with the internal trigger source properly?

Because the internal trigger source automatically re-triggers right after the sweep has completed. Not (significantly) later, and certainly not sooner.

With automatic internal retriggering,  there is no independent timing source for the trigger period. It is directly derived from the sweep period in this case and always exactly in sync.  So there can be no missed triggers.

I particularly and thoroughly compared the external trigger sources with the internally generated signals and made them exactly equal. One is my Rigol DG1022Z and the other is old but very trusty HP3325A.

But making them "exactly equal" is the problem! You have created a "race condition": You try to ensure that the next trigger comes at exactly the same time when the sweep has been completed. But if the trigger arrives only a few µs earlier, the SDG will ignore it. So a little bit of jitter in the trigger period may cause some triggers to be missed randomly. Or a trigger period which is a few µs too short will systematically cause every other trigger to be missed.

Very likely what's going on wrt the AWG sweep triggering.

Well diagnosed 

Best,

[ton4eff]

OK, I'll take the risk to embarrass my self further, but it's like a splinter in my mind... I now understand why the internal trigger works, it's actually generated by considering the end of the actual generated signal. I however think that the very idea of the external trigger source is to trigger independently of the signal. And there should not be any limitation of this matter (while it is in the units specs of course). Because now I can trigger with any signal I wish, except of the one which I need mostly...

[Martin72]

I would then correct that, for obvious reasons:

I found another annoying bug. 

[ton4eff]

@Martin72, I did corrected it, I hope now it looks better?

[ebastler]

I however think that the very idea of the external trigger source is to trigger independently of the signal. And there should not be any limitation of this matter (while it is in the units specs of course). Because now I can trigger with any signal I wish, except of the one which I need mostly...

You can use any trigger signal you like -- you just need to adjust the sweep duration in the SDG2042X accordingly.
(Namely, set the sweep duration a tad shorter than the external trigger signal's period.)

I understand that you have a given external signal and want (or need) to use that as the trigger. Use that signal, start by setting your SDG's sweep duration to the nominal period of the trigger signal, and then reduce the sweep duration until you no longer get any missing sweeps.

In my quick test, I could literally just stay 1 µs below the trigger signal's 14 ms period, and get reliable sweeps. Those were ideal conditions though: I used the second channel of the SDG2042X, connected to its AUX input on the back, to generate the "external" trigger. So the sweep duration and trigger period agreed exactly on the nominal timing, since they were derived from the same master clock. If your trigger period comes from a different time base, it may be systematically off a bit, or may exhibit some jitter. Just keep reducing the sweep time in µs steps until you get stable sweeps.

[ton4eff]

I just tried again, yes it works with 14.1ms and even with 14.05ms external trigger. That will do the job for my purpose. The first time I tested it even worked with 7.1ms. Now, for some reason it wont - it just jumps forward and backward at his will. And I still don't understand why it takes in consideration the sweep signal with external triggering source. It should trigger completely independently, that's why it's "external", right? I again sent a message to Siglent support, let's see what will be their answer (I don't have high hopes...). So, I'm sorry, but for now, I still think that there is a problem... 

PP: I just made another quick test, it seems that there is a problem with every external trigger frequency below 14.05ms.... I'll continue with the tests tomorrow...

[JDubU]

An internal trigger runs off the same clock as the sweep signal generator so they are guaranteed to always be perfectly synchronized.  The end of one sweep triggers the beginning of the next. No possibility of conflict between one and the other.

An external trigger runs off a different clock so there is no inherent synchronization.  What should happen if the external trigger arrives while a sweep is still in progress?
Three choices:

1) Ignore that trigger and wait for the next trigger that occurs when the sweep is not in progress.
2) Stop the current sweep and immediately begin the next one.
3) Let the current sweep finish and begin the next one immediately.

[ton4eff]

OK, so it takes in consideration the sweep no matter if the trigger is external or internal...

[KungFuJosh]

Here's my dumb question:

Does running an external trigger have any delay introduced by the cabling?

[TheDefpom]

I am just speculating here, just to add another perspective.

One thing to consider is the pulse time of the trigger, not just the time between pulses, if the pulse duration is too short is may not be seen correctly as an trigger, OR it may require the pulse to be present for a certain duration of the trigger time, maybe 50%, or 90% etc.

I have not used external trigger on any of my test gear(or even read the page about it) so I am just speculating, but I have come across the need to have trigger pulse durations long enough to maintain the output during the timeframe between trigger pulses on other kinds of equipment, in the situation I am thinking of the trigger pulse had to be active whilst the output was wanted, if the pulse stopped short it cropped the output off too.

[ebastler]

Guys, this really is a solved problem. No need to speculate about cable delays (negligible) or pulse durations (ton4eff uses a 50% duty cycle square wave). It really seems entirely clear to me that the SDG ignores trigger edges which arrive while it is still performing an ongoing sweep.

The first time I tested it even worked with 7.1ms. Now, for some reason it wont - it just jumps forward and backward at his will.

A trigger signal with 7.1 ms period must work as well. In that case, every other trigger is safely ignored because the SDG is still sweeping. So it is equivalent to a 14.2 ms period.

If it "jumps forward and backward", that will be just on your oscilloscope: Because you trigger from the 7.1 ms signal, your scope will sometimes trigger on the active trigger edge, sometimes on the one that gets ignored. Set a trigger holdoff time of e.g. 10 ms on your scope to avoid this.

And I still don't understand why it takes in consideration the sweep signal with external triggering source. It should trigger completely independently, that's why it's "external", right? [...] So, I'm sorry, but for now, I still think that there is a problem... 

The one thing I agree with is the head-banging smiley...

The external trigger means that you can determine externally when a sweep starts, namely at the edge of your trigger signal. But you cannot determine externally how long the sweep takes -- that is still defined in the SDG2042X. And the SDG is designed to always complete a sweep once it was started. If another trigger edge arrives while the sweep is still ongoing, it is ignored. After the sweep is completed, the SDG will be ready for the next trigger edge to start the next sweep. It's really quite simple.

There is another way one could implement this, and that is probably what your Rigol generator does: If another trigger arrives while the sweep is still ongoing, stop the current sweep and start a new one immediately. This will avoid missed triggers, but will give you incomplete sweep ranges instead. I think there is no "right" or "wrong" implementation.

Edit: There is a third way, and maybe that is what you are imagining: Lock the internal ramp generator which creates the sweeps to the external trigger signal via a PLL. In that case, the external signal could define the starting time (phase) and the duration (period) of the sweep. The sweep range (center and span, or min and max frequency) would still be defined in the function generator, but the rate (slope) of the sweep would adapt to the external trigger. I am sure such sweep generators exist, but the SDG is not one of them -- and neither is the Rigol, I believe.

[ton4eff]

I agree, let's close the case. Now in the fresh morning everything makes perfect sense. The difference between the different generators is because they handle the external trigger in a different way. I appreciate the time and patience you have to explain a simple things like that to a noobs like me. But now we have a little bit deeper knowledge about the guts and brains of these new digital generators...

[ebastler]

If you feel that it all makes sense now, I agree, we can close the discussion. But if you should still have some nagging doubts that there is something not quite right with the SDG, please say so, and we can try to get to the bottom of it! I don't want to cut the discussion short if there are still open questions.

[ebastler]

Just one additional comment, in case you are wondering "What will the SDG2042X do after it has completed its 14 ms sweep, and while it is waiting for the next trigger to arrive?".  I just tried, and it will be emitting a sine wave at the prescribed start frequency of the sweep.

In the attached screenshot, CH1 (yellow) is the swept sine wave, CH2 (red) is the external trigger to the SDG, F3 (blue) is a bandpass filter on CH1, defined as a math function in the scope because I was too lazy to connect anything external. The SDG was set to a 14 ms sweep from 9 MHz to 11 MHz; the external trigger was set to a 20 ms period, deliberately longer than the sweep time.

The lower part of the screen shows a time-zoomed view, positioned (as seen from the little narrow rectangle in the upper window) at a time between frequency sweeps. The measurement results at the bottom, and the cursors in the lower window, show that CH1 receives a 9 MHz sine during this time, i.e. the chosen start frequency of the sweep.

[2N3055]

Just one additional comment, in case you are wondering "What will the SDG2042X do after it has completed its 14 ms sweep, and while it is waiting for the next trigger to arrive?".  I just tried, and it will be emitting a sine wave at the prescribed start frequency of the sweep.

In the attached screenshot, CH1 (yellow) is the swept sine wave, CH2 (red) is the external trigger to the SDG, F3 (blue) is a bandpass filter on CH1, defined as a math function in the scope because I was too lazy to connect anything external. The SDG was set to a 14 ms sweep from 9 MHz to 11 MHz; the external trigger was set to a 20 ms period, deliberately longer than the sweep time.

The lower part of the screen shows a time-zoomed view, positioned (as seen from the little narrow rectangle in the upper window) at a time between frequency sweeps. The measurement results at the bottom, and the cursors in the lower window, show that CH1 receives a 9 MHz sine during this time, i.e. the chosen start frequency of the sweep.

A side note, you can use built in frequency measurements for this, together with measurement gate.

[ebastler]

A side not, you can use built in frequency measurements for this, together with measurement gate.

Yep, that works as well and is probaby a bit quicker to set up, thanks. I wanted to try a more "visual" approach to make it clear what's being measured and what the emitted signal looks like -- on the full sweep time scale, the sine wave itself can obviously not be resolved visually.

[mawyatt]

Get a kick out of newbies that immediately claim somethings "broken/bug" because it doesn't "behave" the way they expect, without taking the time to understand the reasoning behind why things behave the way they do!!!

In case of the AWG the decision to allow the sweep to "always" complete could have been based upon this allows the AWG to always synch up with whatever trigger commands are presented and complete a full sweep ignoring everything trigger-wise during the full sweep. Whereas the other option is to allow the sweep to be retriggered during the sweep, thus not completing a full sweep, each method has it's merits!!

This reminds of when handing someone the keys to a Porsche 911. If the potential driver fumbles around trying to start the 911, then discovers the key socket is on the left of the steering column, and excerpts, "those idiot Porsche engineers but the key socket on the wrong side"

Only later do they discover that this dates back to the early days of Le Mans, when the drivers sprinted across the track at the race start, then had to put the cars in 1st gear, release the hand brake and insert key and start the engine all with the right hand (Le Mans rules required the cars be in neutral, with hand brake on). Porsche figured the left hand was doing nothing at the Race start while the right hand was sequencing thru the start up routine, and decided to locate the start key socket left of the steering column so the left hand could insert key and start the engine, all to save a second!!

Anyway, Porsche decided to keep this 911 design (as well as the upside down boxer Flat 6 sitting behind the rear axel) in remembrance of the "old days"

So maybe the concept of a complete AWG sweep regardless of re-triggers dates back to the old days of function generators, altho can't remember how those behaved, getting too old

Edit: Actually now thinking about the old analog function generators when sweeping, this may have been the mode of operation. Utilizing a simple RS Flip-Flop Externally or Internally Triggering the Set and Internally Reset with a Pot Controlled On-Shot Timer (555 ?) which creates the Sweep Period

Best,