Author Topic: Do I really need a 4 channel scope?  (Read 8918 times)

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Online EEVblog

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Re: Do I really need a 4 channel scope?
« Reply #25 on: September 18, 2015, 02:56:18 am »
I have an old Tektronix 2213A 60 MHz analog scope, couldn't I use that if I needed two more channels?

In some situations yes, but most of the time with modern scope you are single shop capturing and analysing the waveforms. You can't do that with an analog scope.
 

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Re: Do I really need a 4 channel scope?
« Reply #26 on: September 18, 2015, 02:57:45 am »
That's exactly my thought on why I don't want to get the 1054Z. The 1054Z doesn't have enough bandwidth.

Most general use for scopes don't need high bandwidth. 100MHz is plenty.
It's common to have a cheaper 2nd hand old high bandwidth scope (even analog) for high bandwidth signal integrity work.
 

Offline nbritton

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Re: Do I really need a 4 channel scope?
« Reply #27 on: September 18, 2015, 03:11:28 am »
Before getting the oscilloscope above, I was in a similar scenario as you: torn between the more featured DS2000 but only with 2 channels, or aiming for the budget DS1000Z and its 4 channels. I ended up getting the best of both worlds with a DS4014, but only because the circumstances conspired to close the deal.

How did you manage that one, the DS4014 costs $2300. For $2077 you could have bought two DS2072A and one DS1054Z! I do have the money for a 4000 series, but are 4 channels really worth that much?
 

Offline sarepairman2

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Re: Do I really need a 4 channel scope?
« Reply #28 on: September 18, 2015, 03:16:19 am »
I want a cthulu channel oscilloscope. i want an infinity oscilloscope that uses transmission line effects in 3 axis
 

Offline FrankBuss

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Re: Do I really need a 4 channel scope?
« Reply #29 on: September 18, 2015, 05:46:58 am »
Unless you need the portability, I would rather have a separate DSO and a computer-interfaced logic analyzer. When working on 16 signals, it's rather nice to be able to use a keyboard to quickly label your signals and to use the mouse to scroll and set move flags. An oscilloscope already has enough buttons and wheels on it. You might need an MSO for a specific reason, I suppose.
I develop digital electronics, but often it is really useful to see one or two analog channels together with the digital signals, for example to see the exact time when an ADC output changes. You can't do this easily with a computer-interface logic analyzer and a separate scope. For me MSOs are necessary.
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Offline fivefish

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Re: Do I really need a 4 channel scope?
« Reply #30 on: September 18, 2015, 06:00:09 am »
Monitoring the differential input and differential output signal (for example, balanced audio)... there goes your 4 channels.
 

Offline TMM

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Re: Do I really need a 4 channel scope?
« Reply #31 on: September 18, 2015, 06:00:30 am »
That's exactly my thought on why I don't want to get the 1054Z. The 1054Z doesn't have enough bandwidth.

Most general use for scopes don't need high bandwidth. 100MHz is plenty.
It's common to have a cheaper 2nd hand old high bandwidth scope (even analog) for high bandwidth signal integrity work.
Worth noting that even if you mod the 1054z to 100MHz, running 4 channels at 250MSa/s can be a bit iffy if you are looking at 25MHz+

I had a DS1052E, sold it and bought a DS1054Z. 4 channels is great and since most of the work I do is low frequency (<1MHz) the sample rate isn't an issue. The things I miss about the 1052E were alternate triggering and having a dedicated trigger input. Sometimes I'm looking at 4 channels of analog where two channels are >1MHz and two channels are <10KHz. Without alternate triggering, I'd be better off having two 2-channel scopes instead.
 

Offline MarkF

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Re: Do I really need a 4 channel scope?
« Reply #32 on: September 18, 2015, 06:49:27 am »
That's exactly my thought on why I don't want to get the 1054Z. The 1054Z doesn't have enough bandwidth. I would like to display up to the 9th harmonic of a 25 MHz square wave with negligible attenuation, this would require a minimum bandwidth of 225 MHz. The MSO2072A (hacked to 300 MHz) has a calculated system bandwidth of 228 MHz, this would be perfect. Psychologically the 1054Z feels like a toy due to its price point and cobbled together features and functionality. If I bought it, I think in the back of my head I would always be wishing I had more scope. It would drive me crazy.
Sounds to me like you've already made up your mind.   Get the MSO4034.  You won't be satisfied with anything less.
 

Offline ebastler

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Re: Do I really need a 4 channel scope?
« Reply #33 on: September 18, 2015, 06:59:53 am »
I would like to display up to the 9th harmonic of a 25 MHz square wave with negligible attenuation, this would require a minimum bandwidth of 225 MHz. The MSO2072A (hacked to 300 MHz) has a calculated system bandwidth of 228 MHz, this would be perfect.

That's a surprisingly specific requirement. I'm curious what application is defining that specific need? Or is it "reverse engineered" from the spec of the MSO2072A?
 

Offline nbritton

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Re: Do I really need a 4 channel scope?
« Reply #34 on: September 18, 2015, 07:51:01 am »
I would like to display up to the 9th harmonic of a 25 MHz square wave with negligible attenuation, this would require a minimum bandwidth of 225 MHz. The MSO2072A (hacked to 300 MHz) has a calculated system bandwidth of 228 MHz, this would be perfect.

That's a surprisingly specific requirement. I'm curious what application is defining that specific need? Or is it "reverse engineered" from the spec of the MSO2072A?

I inferred it by studying the Fourier series of a square wave, the summation of the first five odd harmonics (fundamental, 3rd, 5th, 7th, and 9th) is the first waveform that accurately approximates a true square wave. I settled on 25 MHz because I'm going to be working with computer equipment and it's what I can afford, it also happens to be the fastest square wave that the Siglent SDG1025 can drive.
« Last Edit: September 18, 2015, 08:12:51 am by nbritton »
 

Offline Berni

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Re: Do I really need a 4 channel scope?
« Reply #35 on: September 18, 2015, 09:41:30 am »
In practice i use more of a rule of thumb.

For checking signal integrity like overshoot you tend to need a scope with x10 the bandwidth of your signal. While for just looking at what the signal is doing about 3x to 5x is enough.

A 25MHz square wave will look a bit better on the actual scope because the bandwidth will slowly roll off after its spec, not just suddenly drop off a cliff. So you do get some harmonic content past the bandwidth, just that its attenuated more and more as you go out, making the signals edges round off rather than show this ringing on the top.

Now this does not mean oh i have buses going at 100MHz so i absolutely must buy a 1GHz scope. I seen some pretty horrible digital signals fed in to some of my digital circuits. Yet the thing still kept on working fine. So if the signal looks clean on a low bandwith scope in most cases it is good enough. And if there is weird stuff happening you usually just need to fix the clock signal (Twist a wire with ground for it, use a shielded wire, add some termination resistors or pF caps to fine tune the ring away etc). Where you want to have a really high bandwidth scope is when you are making a product and you want to make sure all your signaling is well within the integrity requirements of the chips. So that variation in chip quality or temperature and other conditions for sure wont cause it to fail due to crap signal integrity.

As people said buy what you need now and then if you need the bandwidth buy an extra old scope off ebay. A 500MHz scope is not hard to get cheep on there if you don't mind it being old. (I recently bought for 6 grand a  4GHz Agilent scope that is still being manufactured)

« Last Edit: September 18, 2015, 09:45:04 am by Berni »
 

Offline Galenbo

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Re: Do I really need a 4 channel scope?
« Reply #36 on: September 18, 2015, 10:00:27 am »
What will I not be able to do with a 2 analog + 16 digital channel scope?
I think most things are "possible", but there's also the "easy" and comfortable aspect of it.

For signal conditioning, isolation and converting, I like it that I can look at 4 steps of the process at 1 time.
Changing 1 component value has an effect in the whole line, and you don't know immediately where a new problem can pop up.
The probes can stay where they are.
If you try and take a cat apart to see how it works, the first thing you have on your hands is a nonworking cat.
 

Offline Galenbo

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Re: Do I really need a 4 channel scope?
« Reply #37 on: September 18, 2015, 10:07:19 am »
I do have the money for a 4000 series, but are 4 channels really worth that much?
Are 4 channels AND big bandwidth needed at the same time?
If you try and take a cat apart to see how it works, the first thing you have on your hands is a nonworking cat.
 

Online tautech

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Re: Do I really need a 4 channel scope?
« Reply #38 on: September 18, 2015, 10:10:47 am »
Might be worth noting that, last I checked them out, Siglent has scopes that are locked to two channels but can be software upgraded to 4 channels for another ~$200.00 if/when you need it. If the scope isn't superfluous/obsolete by then.
Not that I'm aware of, link or model please.
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Offline retrolefty

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Re: Do I really need a 4 channel scope?
« Reply #39 on: September 18, 2015, 10:20:47 am »
 Well i'm an old fart that grew up with just two channels + external trigger scopes. Good enough for me so good enough for you kids. Heck they sent men to the moon when 2 channel scopes ruled the world. :-DD

 Seriously if 4 channels is desirable why not 6 channels, or 8? I'm sure there is a use case for someone out there. I would think that each added channel requires it's own ADC? if so each added channel carries a cost that should be factored in such a purchase decision?

 So to the OP I would advise him to get what he can best afford and if that lands him in two channel land then don't worry about it and just learn to master his new tool. One thing I know about scopes is that the person at the other end of the scope probe tends to be the limiting factor as far as effectiveness and usefulness of a scope no matter the number of channels and features.
 
 

Online Fungus

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Re: Do I really need a 4 channel scope?
« Reply #40 on: September 18, 2015, 10:23:35 am »
Yes!


(And if you're even asking this you're probaby going to be told to buy that DS1054Z anyway, which is a 4-channel 'scope, so  :-//)
 

Online EEVblog

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Re: Do I really need a 4 channel scope?
« Reply #41 on: September 18, 2015, 10:30:57 am »
I inferred it by studying the Fourier series of a square wave, the summation of the first five odd harmonics (fundamental, 3rd, 5th, 7th, and 9th) is the first waveform that accurately approximates a true square wave. I settled on 25 MHz because I'm going to be working with computer equipment

But do you really need to measure the actual signal fidelity to such detail? Most people don't.
Do you know that you can't use the normal probe ground lead to do that?, you need proper high frequency probing techniques.
For looking at 25MHz square waves, 100MHz bandwidth in practice is usually fine because scope bandwidth don't drop off like a brick wall.
 

Offline Howardlong

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Re: Do I really need a 4 channel scope?
« Reply #42 on: September 18, 2015, 11:32:00 am »
If you are doing digital and have an MSO then 2+16ch will do.

Almost all of my work is mixed signal embedded. If I were offered the choice of 2+16 or 4+0, all other things being equal, it's a really tough choice. Probably I'd go with 2+16. Certainly if your intention is parallel busses as you've mentioned in another thread, then definitely, 2+16 over 4+0.

For a while even quite recently I used 2+16 in the lab on a daily basis even though I had 4+16 available, the 2+16 was just a much more easy to use scope (the 2+16 is an Agilent 54642D Megazoom 500MHz/2Gsa/s, the 4+16 is an Agilent 54831D Infiniium 600MHz/4Gsa/s Windows based scope with a boot time to match). I had the 54642D trigger permanently hooked up to a 54622D, so I could get a couple more analogue channels if necessary on the odd occasion. The use case for that was usually when doing switch mode power supplies, although even four channels is often marginal when doing SMPS!

I too was brought up on 2ch CROs, when I could even get my hand on a scope at all that is, and you can do an awful lot with that, and usually you can do all that you need, it's just much more convenient with more channels, there's less manual pen+paper work involved.

It sounds like you may be having a case of what I call "analysis paralysis", and I don't mean that in a negative way, I suffer from this affliction regularly: just keep in mind that any scope is better than no scope at all!
 


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