Hi. Just a quick follow-up to the previous video where I showed how you can make your own do-it-yourself Emi probe for 10 bucks including the little amplifier and a lot of people pointed out the irony of making a $10 probe and then using it on like $1,000 or $1,500 spectrum analyzer to make it work. And yeah, well, fair enough, But a lot of people ask, can you actually use this a $10 EMI probe or any Ami probe on a regular oscilloscope? I Use the FFT function to turn your oscilloscope into a spectrum analyzer. and yes, you can, so let's take a quick look at that.

And also there's other ways to do a cheap spectrum analyzer as well. And I've got on order a one of those USB SDR software-defined radio spectrum analyzers. So I hope to do yet another follow-up video on that. Okay, so what I'll do first is just get a baseline right across the crystal on this gigatron board here just so that we can compare it with various scopes.

Here we go: I've got a 100 megahertz pan. reasonably low frequency if you're looking at the far field. emissions are in like a regular EMC compliance test. If you took your product to an EMC test house, then depending on the type of product, a typical frequency range might be from 30 megahertz to one gig.

but you can definitely get a decent look at things with just like a hundred megahertz span. and stuff like that depends on the product that you're working with. Let's get that up. Put that right over the crystal like that and we can freeze that.

So there you go. Let's see if we can get a similar response with a similar Peaks and noise floor and whatnot. But really, when you're doing these sort of near-field HRE field magnetic or electric field probing, you're not really doing a quantitative measurement as so like an absolute quantitative value. You're really looking at the spectrum and it's just seeing if any Peaks actually pop out here and it's something you know.

You move this over your board and you have a look in real-time and see if anything just pops out like that and then you go aha what friend you go in there, you measure the frequency, determine what frequency that is, and if that's going to be an issue, that's why it doesn't really matter what size are loop you used here, whether or not it's calibrated in quote marks I mean the professional probes? Yes, I had to dip the end in yellow because I peeled it back. it didn't stick very well By the way, need a couple of more coats on that? I Need to get the the liquid dip one instead of the spray one anyway. So although these are professional ones might come with characteristic, our plots like this: it shows you the coupling lost performance over frequency in this case. it's a three gigahertz span here.

But really, the calibration in quote marks doesn't really matter for these things. You're just looking at a sort of like a relative signal just jumping out of the noise floor. Basically Okay, so let's just try a typical scope here: I've got the brand-spanking-new Our Keysight for Channel 1000 X-series 200 megahertz analog bandwidth for channels. It's got a reasonably nice FFT Function doesn't have a huge number of points on this thing.

what is it? 64 K point FFT I think But it's going to do the business now. This isn't the best scope if you're looking at low amplitude signals. It does have a 500 micro volt per division range, but that's not true. 500 micro volts per division.

It's just software magnified. You might be able to see that in that the pixels are actually doubled, but fortunately you don't need a like a really good low signal level front-end scope because that's what our amplifiers for. This is a 20 DB amplifier one the cheap $7 one from eBay This one happens to be 30 DB You can get 40 DB once if you're worried about the noise fluoroscope impacting it. just get a higher gain preamp.

That's it. So if you want to get these on eBay just search for RF pre amplifier and there's like dozens of different models. Do a set our pro but just one to one because we haven't got our X Ten probe here and we'll just set it to at like 200 millivolts per division. and I'll put the probe over that crystal again and Zak the same location that we had for the spectrum analyzer and look at that and stay down a hundred millivolts per division.

This is not low amplitude stuff, even with a 20 DB gain amplifier. If you get a higher gain amplifier, it's going to be higher again. but you know if I put it elsewhere on the board like directly over the room. For example, 200 millivolts per division.

some really high level stuff that's over the RAM I'll just show you that on the board here. see that's over the room address decoder. You can see that signal really changing in real time. It's great.

that's what you can do probing, but of course we can't see much in the time domain so we have to turn on our FFT. You can switch it to the frequency domain exactly like we get over on the spectrum analyzer so we can see the frequency Peaks cuz that's what we're really interested in. Alright, now we can actually leave the analog signal on if we want this and generally switch that off because it just adds clutter. and if we put it over the crystal like this, then we can start to see some spikes in here.

So we use our controls here. Let's have a look at the FFT We're at a hundred megahertz span, so there's ten divisions on there. so it's ten megahertz per division. Doesn't actually tell you that down here.

That's ten megahertz per division. Just gotta use your noggin. And our center frequency is 50 megahertz. So we're just using a hand in window and vertical units in DBS Doesn't matter.

You might have seen me use DB micro volts on the spectrum analyzer. I Just prefer to work in that for this sort of thing. It doesn't really matter it. We don't really care about absolute values on this near field type measurements, really.

Oh, it's more of a comparative thing and trying to find peaks in the value here. Anyway, move this up and we can change our scale here. Let's move that up there we go, and of course we can change our horizontal to get more resolution. You can see the resolution FFT resolution there 122 kilohertz.

so that would be equivalent to our spectrum analyzer there, which we were using a hundred and twenty kilohertz resolution bandwidth filter there, so maybe some averaging or something like that. Get it a little bit better and then we can go in there with our cursors and then we can measure our frequency. Bingo! Six Megahertz. That's our fundamental clock of course, Twelve megahertz and so on.

Now, because it's hard to actually show these two side-by-side what I've done is actually screen captured the spectrum analyzer and in my video editing software here I can overlay it. That's kind of cool. It's got a similar sort of shape, but you can see that the peaks are the same and if you have a look at like this one here, for example, it's sort of like you see that that's the lower amplitude to all the others. some of them are a bit higher.

but and stuff like that, this one is correspondingly low like the spectrum analyzer one. So it's doing the business. And as I said, all you care about is those Peaks popping out as you go over the board. you might compare board PCB revisions for example.

So you might go aha like I've got this big spike here, for example, might come out so you might realize that you goofed up the PCB layout. so you might Rhys pin your board, tighten up the loop area to actually get that down, or do whatever measure you want to do. and then you retest it and you should be able to then see that particular spike drop by X amount of DBS or whatever so you don't need a quantitative value. doesn't really matter to get a comparative difference when you make changes on your design.

That's what it's all about. So you can see how even a low-end scope like this with its FFT functionality is more than good enough for the job of doing this. You don't need an expensive spectrum analyzer. you can just do it.

make your own probe for like five bucks. Buy another $10 preamplifier Bob's your uncle. Let's actually add a 50 ohm Terminator to that and see what difference that makes. So there you go.

It does get a little bit closer perhaps to our response over here and you can actually see the general trend. So really, the every gene is probably the best. just love the average in effect. Mm-hmm yeah.

and if I just dial that back to a similar sort of like amplitude relatively speaking to what we've got on the two screens here, you can see yeah, it's It's doing quite a reasonable job and if we try a scope with it sort of notoriously poor. FFT Functionality: The venerable Roy Gold Es 1054 Z which is otherwise and is still an excellent bang per buck scope. Let's see what we can do with that. As you can see, we can actually get that to do the business as well even though it's you know.

update rate and it's a number of Fft points isn't great, but yeah, let's have a closer look. 18.8 Killer DB Volts She just got serious and as you can see there, it kind of works where it are the same ten megahertz per division. Here you can see some spikes in there, but it's not terrific. But the trick with this is is that you'll notice over here it's got trace.

Now the latest firmware. The original firmware only did FFT based on the the trace data ie. the displayed data, but if we actually change that, that's why the resolution isn't that great. but if we change that to memory, there you go.

Bingo! That does it on the entire memory and you'll notice that we get the expanded frequency range now as well. and that's much better. But it's It is 16 K points, but it still does the business. Yes, the updating is slow on this thing, but like it is still actually usable, it's just not as great.

16 K points versus 64 K points. There's a big difference, but the information is there, so that's the main thing. One of the annoying things about the RAI goal though is that you can't turn off Channel 1 for example, because then your data just vanishes so you've got to actually have Channel 1 on the screen. and if you go into the math function here and you and it's like half display which is the split display and if you go into the full display, it's like so there we go.

We can't actually get rid of it like that because it's the displayed window moving that out so it's still actually capturing the data in there. It's possible to do the business with there I go. It's just a bit slow and clunky. that's all.

Just trying to change the offset on this is just an exercising in frustration. It'll eventually come good. but hey there it is. So we can actually go into the curses here and we can actually change our units to Hertz Six megahertz and our 12, etc etc.

does a reasonable job at the 16 K points isn't great and the slowness of it, but apart from that you can coax it into working no problems. Now let's have a look at the siglent SDS 1202 XC This is a two hundred megahertz our bandwidth scope and it gives a pretty darn good account for itself as I mean exclusive mode at the moment I Really like the split screen mode is really nice. super fast updating of course are the FFTs is faster than the Rye goal but you know, not super quick and I like how you can overlay them on top. it really like the contrasting colors with the white the yellow there really works or you can just go exclusive like that and we can actually improve that because we're normal display at the moment.

but if we go in and do some averages that is pretty jazzy. that's doing the business very nicely. I Like that, but there are some scopes that are just absolutely useless. this oh one XDS 3202 which actually has a 12 and 14 bit convertor in it.

So in terms of like you know, like resolution, it's actually quite a good scope, but it's FFT functionality is absolutely useless I can't even get it to match the parameters of the other scopes with ten megahertz per division, it's just you can't do anything with it and the road. And Schwartz HMO 1200 series Very cute little scope. It's giving an excellent account for itself. Look at this.

It's a little bit slow because I've got all the average in turned on I've got a hundred and thirty 1k points here. 128 K Cleo any window and that is a superb result. Look at that. Wow It does take its light a little bit more fiddling on this to actually I get what you want on the FFT window.

but that is that is beautiful. We can actually lower the points. There's our 65 K points 32k points Anyway, that's 16k points us the same as the Wry Goal for example, and we're getting a much better response on the road. And Schwartz here.

not only is it faster, but look at the noise floor is much better. It's those signals are really popping out of that. So I'm loving that. And we have a quick look at the GW in Stick GDS 1104 B because this thing has one Meg points FFT and look, this has to be the fastest updating of all of and that is insane.

Look at that. Unfortunately, it's a bit inflexible in that you can't actually turn off the analog Channel Otherwise, it actually vanishes. and if you try and change the position of it, if you go up off the screen, it's not just the display, it's actually the ADC window. So you start to see your signal vanish like that.

But one of the reasons is so fast where we are only on 10 K points mode. If we memory mode if we go to 100 K points, well look at that. Now we're talking 1 Meg points. It takes time for its first, but but even at 1 Meg points which is different, this is the sample memory.

This is not the FFT number of FFT points. This one actually takes a bit of fiddling around in terms of like selecting the correct thing here. but there we go. We've got it.

And you can see the ridiculously fine resolution in there. It's just nuts. Unfortunately, it doesn't seem to have an Fft averaging function. I've got the I've got the channel averaging function turned on if we go into a choir there.

I've got that done, but it doesn't look like it has a separate average for the FFT. Yeah, it's just all kind of like really messy. I'm not too taken by it. Let's have a look what a higher end scope can do one with not only a true 1 millivolt front end, but also a 10-bit ADC as well.

So this is a rode Schwartz RTB - double o for very nice scope. and look at the ridiculously fast updating on this. I've got the resolution bandwidth. You can just go in there and set that.

It's very nice. You can just like type it in and the span. It's beautiful anyway. like it is quick.

It is super burly fast look at that. but you might notice that. there's a lot of crap in there. So if you actually go into the wave for so I'll got our hand in waveform as per normal, that's our spectrum.

We can actually go in there even though I've got average in for the front end. Now it's actually got both on that screen together. You can see that so that's a real nice feature so you can have both turned on. We can just turn the spectrum off and bingo there's our average and look at all that beautiful detail just popping out of the noise there.

That's fantastic. You notice how it's like going up and down, up and down very slowly like that. I Believe this is like beating between the averaging because this has got two different types of averages. One is the FFT processing average which we've got down here.

the other if we go to the acquisition menu. I've actually got the input sampling in average mode, so if we change that back to sample mode, you'll notice that it's It's kind of like it's different now, but if we can do both, we can pull out extra detail now. I've got ten averages on both and we just pull out the extra detail there. It's very nice.

The other thing I Really like about this scope. not only the FFT detail we're getting in here, but look. I can just draw stuff. Look at that like just little things like just popping out on the noise like that one in there.

for example, like this little thing popping out in there, it's just. it's absolutely terrific. Smiley face? There you go. But of course that's a much more expensive scope than the other bottom of the range.

Once we've looked up, you can see that you know while the performance: II This is brilliant because it's got a 10 bit analog to digital converter, a true one millivolt at noise flaw, and really super fast FFT Processing with large number of points. we're really extracting the detail out of that. Actually more. You could argue more so than we were getting with the Reigle spectrum analyzers over here.

But and granted, this, this scope is actually much, much more expensive than this. My goal with spectrum analyzer, which is a bottom of the range, then granted. Dave CAD So there you go. These are.

you know, a reasonably low-end scope. A low bandwidth one can give a reasonable account of itself and can be fairly useful for troubleshooting boards like this. We can just go over there. we can see various Peaks You can see that they vanish.

You can manufacture different size our probes to get different sensitivities. You can really do live probe in with just your scope. Works a treat, no worries. but you've got to have a nice fast FF T mode and give it slow as a wet week and it's got a crap a resolution like the Rygel one for example.

It might be able to press it into doing the business, but it's not as nice as a high number of points FFT And you know, real-time updating. So and it works. A treat. you don't need thousand dollar or fifteen hundred dollar spectrum analyzer, but as I said, I've ordered one of those I'm SDI USB dongle things and in theory should be able to use this with a SDR dongle for a poor-man's spectrum analyzer.

But anyway, say that for another video if you like this one. please give it a big thumbs up. As always, discuss down below: catch you next time you.