Hi just a quick video and yes, this one will actually be quick. I'll try and do it in a single take. This is a followup to my last video which was the second delay line video where I was playing around with a delay line and I was putting a burst uh signal into it and we're measuring the delay and looking at the burst coming out of one of these power delay lines. Now somebody asked um I mentioned in the video that uh, you know there was the screen Jitters like this because the triggering wasn't set up correctly and I didn't bother because I was playing around with single shot I was single shot capturing it and you can go in there and you can view the waveform just fine.

So they wanted to ask how do we fix that trigger Jitter like that and it turns out I've already done a video on this. It's called trigger hold off and I go. It's about 20-minute video. It explains how to trigger like this, but but there's actually uh, three ways to uh, trigger off this thing and make it stable.

So let's take a look at them. now. why does it trigger? um I Be very brief because it's in my more detailed video. but basically, when you've got a burst, a swaave burst like this, we're triggering off the yellow waveform here and you'll notice that the Jitter is basically the same width as the packet of data like that.

And that's no coincidence because if we single shot capture this thing, this scope is just set for basic triggering. just Edge type triggering. um and uh, set up for you know it's triggering off the yellow waveform Source One positive going Edge absolute basic trigger. Now it's triggering at that point there.

you can see the triangle. There it is, but it doesn't know whether or not to trigger off that one or that edge or that edge or so on. It doesn't know which one of those to trigger on. and depending on when you run this thing, when you uh, run it like that and it's trying to get a trigger.

depending on when the rearm time of this scope is, you could actually get the trigger point being anywhere within that period there. It's not going to trigger in this Dead period because well, it doesn't transition through the trigger point there. there's our trigger level there. It's sort of set halfway between there, so it doesn't know which one of those to trigger off.

So that's why it can be. You can get trigger Jitter up to the width of that. so one way to. Oh, and and by the way, um, depending on the rearm time, that depends on the input fre the frequency you're inputting to this thing.

sometimes you can actually fluke it, but because we don't have much of a dead time in there if I actually change the number of Cycles here. if I reduce the number of Cycles then there's more chance you see how it becomes more stable. I've only got 16 Cycles now, or there's only six Cycles Now you see how it's more stable is because less chance that the rearm time is going to be within that period there based on the whole period there. it's just pure statistics unless you fluke the exact input frequency to make it stable.

So if I increase the number of Cycles, you'll see that the Jitter increases like that. And likewise, if I say increase the uh burst period. Like this, it has the same effect. It can actually make it more stable because the um odds of it uh triggering within there are quite short.

It's more likely that the rearm time is going to appear somewhere within that long Dead period. So if it appears, say, halfway between here by chance, then it's got to wait until the next Edge and you will get it to trigger off that very first Edge There, there's just more chance of that happening. So I'll change this. Uh, change this back to get ourselves a really horribly triggered waveform, shall we? So let's go in.

there. number of Cycles Increase those bang. Okay, so we're we want to trigger off this thing here. Now the way we do it is with trigger Hold off I've done a whole video on this.

so let's go into the mode coupling menu here and there's an option here called hold Off and this is available on analog Scopes as well as Dig and it's currently set to the minimum value of 40 nond. so I Won't go into the details but watch my other video if you want to see it. Now we can increase that value And because this burst here is 20 microc, if we if it's under 20 micros then it can still trigger on parts of that waveform we want it to delay or hold off. It's why it's called hold Off Trigger hold off, hold Off for that entire 20 microc period because if it happens to to trigger off the first uh Edge there then it needs to hold off for at least 20 micros to make it stable.

So if we increase this hold off value here, you'll find at 20 micros it will magically become stable. There we go: Four micros, 5 6 It's a bit touchy I Don't want to turn it too fast 10 We're still not stable, but as soon as we hit that 20 micros seconds here we go. we're almost there. Bam, There we go.

We're just over 20 micros and now we're stable at all time bases there and it's always going to trigger off that first period because the hold off trigger hold off is going to occur regardless of which random cycle the. the first time you run it, it might trigger in the center there or something like that, but after that it's going to rearm only during the Dead period so it will always trigger on that. very F If it rearms in this Dead period, it waits until that very very first cycle. Bingo There you go Tri that's using trigger hold off to stabilize your waveform and that's the uh, traditional way to do it.

Now the next way you can do it is using a more advanced trigger type that you can get on these modern digital. Scopes Let's trigger on a pulse width here. So we want to go down select pulse width there and we basically want to trigger on uh, we're triggering on the source, which is uh, the yellow waveform channel one again and we want to trig on the negative part of that. So we want to trig on the negative when it's greater than a certain amount of time.

So when when we get to that Dead period between the burst we want to trigger on that, you can see it's still unstable because it's set to two nanocs which of course is um, less than the one one period. Um, less than the individual. Uh, I'm feeding at a 10 MHz signal so it's less than that. So if we just increase that value here, let's oh, increase that 6 nond 8, 12, 15, 20 nond.

All we have to do is make it faster than that cycle time and Bingo There we go at about 60 OD NS There we go. We now have our nice stable waveform so you can do it using that pulse width trigger. and the third option for doing this because we're using in this particular case, an external function generator to generate that burst signal. Any good function generator like this will have a sync or a trigger output that will generate a trigger pulse at the start of that burst because we want to trigger off the start of that burst there.

And that's and this function Gen will actually generate a trigger pulse output during that burst period. So it it will like generate a gating or trigger pulse or synchronize ation pulse whatever you want to call it for that particular thing. So I've set it up, it'll output that synchronization pulse. A lot of function Gens might even be um, output that by default and there's various options for that.

You can have negative going positive going. So what we need to do go into our trigger menu here our source here. instead of being channel one, we don't want to trigger off our signal anymore. we want to trigger off our external signal.

Bingo There it is. and we can display that by turning on Channel 3. There there is that sink pulse. Check it out.

Exactly there Where as soon as it goes here, we want to trigger off that. and once again, we can use our trigger level here and we can cause that make that go unstable eventually because it's now triggering where trigger level is working off the external trigger pulse. But that's the third option to do it. So there you go.

Piece of cake for triggering on complex signal. Well, this isn't really complex, it's just a simple burst. So there're the basics once again. I've done a whole tutorial on trigger hold off which uses um, basically this same example and it shows analog and digital Scopes as well.

So if you like it, please give it a big thumbs up if you want to discuss it. jumping over to the Eev blog Forum Catch you next time.