I want to know what good for is that Bandwidth in a DSO

Thread Starter

q12x

Joined Sep 25, 2015
1,467
- I want to know what good for is that Bandwidth in a DSO !
With examples! What is BEST used for? Why is so important?
I mean... I know I heard some guys, on youtube videos and even here on the forum, who have old types osciloscopes, before these DSO models appeared, in 2000 I guess or so, they told me theirs worked at very low bandwidth. Like 10 or 5MHz.
Also I was reading a post of a romanian compatriot that bought the lowest bandwidth DSO from the list, for a bit more cheaper price than on the original website. That DS1054Z at 419 USD, he got it at 401 USD from here in romania as a 'cheap' offer. (Is still not cheap for me)
The actual page: https://www.rigolna.com/products/digital-oscilloscopes/1000z/
1665779578618.png
Thank you !
 

Papabravo

Joined Feb 24, 2006
19,612
The bandwidth of the amplifiers in any scope, analog or digital, is related to the highest frequency signal that you can reliably observe. If you are doing mostly audio work the 1 MHz.(1E6 Hz.) is plenty fast enough for signals in the 20 to 20 kHz range.

If you are working with RTL, DTL, and Early TTL logic a 10 MHz scope was the minimum useful device.

As logic speeds increased that was raised to 200 MHz.

For work on RF circuits for the cellular industry may a 2 GHz. device might be required.
 
Last edited:

Thread Starter

q12x

Joined Sep 25, 2015
1,467
Thank you @Papabravo , excellent explanation and examples !!!
So higher MHz matters. Damn. And all the prices are MHz dependent. Double damn.
I was curious if you or anyone else here, have some second hand GOOD oscilloscopes for sell, and in what price range.
Like for one like me. Or old brand new stock is even better, but with reduced prices than the new stuff. Or websites that you know for sure they have lower prices. Ebay and Aliexpress excluded since they have the same prices like everywhere else, I check it numerous times and I know it already.
 

nsaspook

Joined Aug 27, 2009
10,708
Thank you @Papabravo , excellent explanation and examples !!!
So higher MHz matters. Damn. And all the prices are MHz dependent. Double damn.
I was curious if you or anyone else here, have some second hand GOOD oscilloscopes for sell, and in what price range.
Like for one like me. Or old brand new stock is even better, but with reduced prices than the new stuff. Or websites that you know for sure they have lower prices. Ebay and Aliexpress excluded since they have the same prices like everywhere else, I check it numerous times and I know it already.
Spend a little more on a modern DSO with signal decoding and capabilities.
 

Papabravo

Joined Feb 24, 2006
19,612
The first installment loan most people get is for a car. In my case it was for a Tektronix 2236 100 MHz portable scope with a VF display for digital readout of voltage, time and frequency. Pretty cool for 1980,
 

WBahn

Joined Mar 31, 2012
27,903
No one can recommend what a suitable scope for you is unless you tell them what it is you want to use the scope for. As Papabravo pointed out, if you are interested in audio, then you can easily get by with an old Heathkit scope with a 2 MHz bandwidth.

Perhaps the better way to come about it is to establish what your budget is for a scope. Then find the best scope you can for that price. Then ask if that scope will actually meet your needs right now and perhaps for a bit into the future. You aren't committing to this being the last, best scope you will ever have. If that scope is good enough, buy it and be happy with your new toy. If it isn't, the use the knowledge you gained in determining if that scope was good enough to go find a scope that IS good enough. How much more is it than your budget currently allows? If you did have that money, would you be willing to spend that much on a scope? If so, how long will it take you to save up the difference if you are aggressive? Then get to saving, looking forward to the day that you will get to play with your new toy.
 

Thread Starter

q12x

Joined Sep 25, 2015
1,467
Speacking from fv pov, I'm more an automation type of guy. Im less into radio or mobile phone/tablet. So going on your last idea, I made a quick search for crystals to check their MAX fv and they are at max 300MHz.
I go and look at the wi-fi and bluetooth as well and here is what I find. I only hunt for the maximum frequencies in this search.
1665817669734.png
Also like @nsaspook mentioned, "Spend a little more on a modern DSO with signal decoding and capabilities." But that will jump up the price with probably another 1000$. So thats no bueno. But it will be very nice to have these options, mmmm. Especially in automation.
- Beside >signal decoding<, what else is very important to have? Especially for automation line.
I then go into 7400-series frequency list and I couldnt find any concludent answer, and absolutely nothing from Wikipedia, which was shockingly odd. The same for TTL logic IC's. Nothing. Hmmm. It must be up to 200MHz as papabravo said. Im not sure if logic IC's are quartz dependent, because if they are, then it will jump them to 300MHz. I know MCU are quartz dependent. But CPU ?
1665819361595.jpeg
These NXP are MCU and CPU. Then the Microchip:
1665819582359.png
Ok... haha.
In general CPU fv:1665820016876.png
What is using a CPU for such (4.3GHz) high fv if not a quartz?
Im doing a bit of homework here live. Haha. I want to get a better idea of how things tick, literally. Haha.
So the conclusion is simple.
The optimum DSO for --ME-- is in accordance with the highest crystal fv, so a 300MHz. For the moment and as my first professional DSO.
 
Last edited:

WBahn

Joined Mar 31, 2012
27,903
What does the highest frequency AT-cut crystal frequency have to do with using a scope for working with automation?

What matters is the frequency content of the signals YOU want to look at.

As for how high frequencies are generated, this is commonly done using a relatively low reference oscillator and then a phase-locked loop driving a voltage-controlled oscillator (VCO) that has a divider circuit that is compared to the reference oscillator. Just as an example with made-up numbers, let's say that the reference oscillator is 10 MHz and the divider is 4096 (e.g., a 12-bit counter running at the output frequency). Then if the VCO output is 4.096 GHz, it will compare equal to the reference oscillator. If the output is a little slow, it will be less than 10 MHz and the PLL circuit will increase the voltage to the VCO to raise the frequency back up (it's more involved than than this, since it is a "phase" locked loop, but the general idea should be enough for this discussion).
 

Thread Starter

q12x

Joined Sep 25, 2015
1,467
Im making an idea right now, I really dont know these things. I mean, I am forming an idea by looking more close to them.
I really dont know what I need or what is best. Im not so specific either. Im an 'experiementalist' so today im on one side of things but tomorrow I may change. I dont want to cry often after (IF) I buy this thing.
 

Ian0

Joined Aug 7, 2020
6,714
There are plenty of signals in projects that you are working on that you perhaps don't need to look at.
For instance, on a 200MHz microcontroller, the 200MHz signal is made inside it by a phase locked loop. You might only need to see whether the crystal that supplies the reference frequency is oscillating, and that might be only 20MHz.
For RF, you rarely need to look at the carrier waveform. You are probably more interested in its spectrum so if you are doing radio a spectrum analyser would be much more useful.
if you are just using a radio module (either 433MHz or 2.4GHz) with a microcontroller, you might want to look at the data stream going in or out, but it is unlikely you might want to look at the RF waveform
Unless you are working with really high speed micros, I'd bet that you would never go beyond the capabilities of a 50MHz scope.
 

WBahn

Joined Mar 31, 2012
27,903
Im making an idea right now, I really dont know these things. I mean, I am forming an idea by looking more close to them.
I really dont know what I need or what is best. Im not so specific either. Im an 'experiementalist' so today im on one side of things but tomorrow I may change. I dont want to cry often after (IF) I buy this thing.
Then go for a cheap, used one and start using it to find out what it is and isn't useful for. You'll find that in a lot of cases, you might WANT to measure signals that are at frequencies higher than your scope can deal with, but that with some cleverness you can get the information you need while looking at a much lower frequency signal.

After a while, you'll have a much better idea of what bandwidth and other features you really NEED.
 

Thread Starter

q12x

Joined Sep 25, 2015
1,467
Well, I already have a DSO138 for experimenting so far. I have it for 3 years or so.
1665826121022.png
What I dont like on it: It has a very unclean waveform, full of jag and stairs and noise. Not at all clean.
Then, I recently find out it is not suitable to measure logic IC's, so under its minimum limit of 10us.
I dont use it THAT much so a better osciloscope will most probably catch dust for a good percentage of time.
But it will be cool to have one though.
 

Thread Starter

q12x

Joined Sep 25, 2015
1,467
Does exist in this big world second hand oscilloscopes at lower prices than the new ones?
I never find them, maybe you can direct me to some websites that you may know. Doesnt matter what country they are. Just to be cheaper than the new ones.
 

dl324

Joined Mar 30, 2015
15,462
It has a very unclean waveform, full of jag and stairs and noise. Not at all clean.
That's a feature of virtually all DSO's because they sample waveforms and have finite resolution, so they quantize the input data. That's one of the reasons why Jim Williams preferred analog scopes.
not suitable to measure logic IC's, so under its minimum limit of 10us.
The DSO138 bandwidth is specified to be 200kHz. It would have trouble with 100kH square waves. You need something with a bandwidth of about a magnitude faster than that to view decent edges.
1665844250362.png
I dont use it THAT much so a better osciloscope will most probably catch dust for a good percentage of time.
I use a 1970's era Tektronix 7704A (200MHz) analog scope with 2 7A26 vertical amplifiers and a 7B53A timebase for my bench scope.

They're big, but you might be able to find a Soviet knock off of the Tek 76xx (about 100MHz). They might have copied the 7603 with the big screen... I like to use one for 7D20 (70MHz DSO) and 7D01 (16 channel logic analyzer) plug-ins.
 

Thread Starter

q12x

Joined Sep 25, 2015
1,467
The DSO138 bandwidth is specified to be 200kHz.
Good for you to bring up this specs. It didnt occur to me to look at the bandwidth of my "hercules" DSO138. So its a 200KHz, what a joke, hahahaha.... I know it in my soul this is waaay too porn of an DSO ! Ha.
1665846443118.png 10us like I said, see? Ha.
 

MrChips

Joined Oct 2, 2009
27,695
If you are on a tight budget a DSO138 is better than nothing at all.
Alternatives are a PC scope, a USB scope, or small/handheld/pocket scope.
My first oscilloscope which I still have is a 15MHz Tektronix 422.
 

dl324

Joined Mar 30, 2015
15,462
10us like I said, see? Ha.
That's only meaningful if you're viewing analog signals. For digital, you need to be able to view at least the 5th harmonic (multiple of the fundamental frequency) because a square wave consists of the odd harmonics of the fundamental frequency.
 

nsaspook

Joined Aug 27, 2009
10,708
Speacking from fv pov, I'm more an automation type of guy. Im less into radio or mobile phone/tablet. So going on your last idea, I made a quick search for crystals to check their MAX fv and they are at max 300MHz.
I go and look at the wi-fi and bluetooth as well and here is what I find. I only hunt for the maximum frequencies in this search.
View attachment 278460
Also like @nsaspook mentioned, "Spend a little more on a modern DSO with signal decoding and capabilities." But that will jump up the price with probably another 1000$. So thats no bueno. But it will be very nice to have these options, mmmm. Especially in automation.
- Beside >signal decoding<, what else is very important to have? Especially for automation line.
I then go into 7400-series frequency list and I couldnt find any concludent answer, and absolutely nothing from Wikipedia, which was shockingly odd. The same for TTL logic IC's. Nothing. Hmmm. It must be up to 200MHz as papabravo said. Im not sure if logic IC's are quartz dependent, because if they are, then it will jump them to 300MHz. I know MCU are quartz dependent. But CPU ?
View attachment 278462
These NXP are MCU and CPU. Then the Microchip:
View attachment 278463
Ok... haha.
In general CPU fv:View attachment 278466
What is using a CPU for such (4.3GHz) high fv if not a quartz?
Im doing a bit of homework here live. Haha. I want to get a better idea of how things tick, literally. Haha.
So the conclusion is simple.
The optimum DSO for --ME-- is in accordance with the highest crystal fv, so a 300MHz. For the moment and as my first professional DSO.
For most embedded systems you almost never probe directly the system clock. Typically a lower frequency clock source is phase-locked into the higher clock inside the processor.

A SDS1202X-E 200 MHz is under $400.
https://siglentna.com/digital-oscilloscopes/sds1000x-e-series-super-phosphor-oscilloscopes/

Some trace shots I've posted from mine. Well worth the money for a first value scope.
https://forum.allaboutcircuits.com/threads/pic32mk-mc-qei-example.150351/post-1617150
https://forum.allaboutcircuits.com/threads/pic32mk-mc-qei-example.150351/post-1618239
https://forum.allaboutcircuits.com/...nd-sensor-node-for-canbus.189388/post-1767408
 
Last edited:

MrChips

Joined Oct 2, 2009
27,695
My go to oscilloscope is a 100MHz Tektronix TDS220.
As spook says, you don't need to look at the 200MHz clock signal on an MCU.
On the STM32F407 project I am working on right now, the highest clock signal I am looking at is 42MHz MCO1.
Meanwhile, the MCU is being clocked at 168MHz.
 
Top