Author Topic: Oscilloscope bandwidth - is jump from 100MHz to 200 MHz significant?  (Read 23662 times)

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Offline IDEngineer

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Re: Oscilloscope bandwidth - is jump from 100MHz to 200 MHz significant?
« Reply #25 on: February 12, 2020, 04:29:35 pm »
Just so, but it is worth knowing the conditions under which you do need more bandwidth, and the consequences of having less bandwidth. There is no substitute for bandwidth.
I'd argue the other way. In many circumstances you can mentally compensate for insufficient bandwidth. But you cannot "fake" your way to a missing third/fourth channel - they're either present or not. Sure, theoretically you can use two scopes with a shared external trigger... but then you still can't compare phase on a single screen across all four signals.

Bandwidth rolls off gracefully. A lack of channels is a brick wall. IMHO always buy four channels, and then get as much bandwidth as you can afford. (Of course there will always be edge cases where this rule doesn't apply, I'm talking about the generic "I need a single scope for all around use" situation.)
 
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Online tggzzz

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Re: Oscilloscope bandwidth - is jump from 100MHz to 200 MHz significant?
« Reply #26 on: February 12, 2020, 05:07:48 pm »
Just so, but it is worth knowing the conditions under which you do need more bandwidth, and the consequences of having less bandwidth. There is no substitute for bandwidth.
I'd argue the other way. In many circumstances you can mentally compensate for insufficient bandwidth. But you cannot "fake" your way to a missing third/fourth channel - they're either present or not. Sure, theoretically you can use two scopes with a shared external trigger... but then you still can't compare phase on a single screen across all four signals.

Bandwidth rolls off gracefully. A lack of channels is a brick wall. IMHO always buy four channels, and then get as much bandwidth as you can afford. (Of course there will always be edge cases where this rule doesn't apply, I'm talking about the generic "I need a single scope for all around use" situation.)

Well, that's a necropost!

The answer is "it depends on what you are doing", and what other equipment you have. You aren't limited to a single tool.

Basically I've found that in the analogue domain 2 channels plus a trigger are neccesary and sufficient. But in the digital domain 4 channels are woefully inadequate;  you often need ~16 channels.

So, use the right tool for the job:
  • use an (expensive) scope to do measurements in the analogue domain. Only a scope can assess logic signal's integrity and you simply cannot mentally fill in the "missing" bandwidth
  • thereafter flip to using a (cheap) logic analyser in the digital domain. You will have far more than 4 channels, and triggering/clocking/filtering are a far better way of ignoring irrelevant signals
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline IDEngineer

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Re: Oscilloscope bandwidth - is jump from 100MHz to 200 MHz significant?
« Reply #27 on: February 12, 2020, 05:19:58 pm »
You aren't limited to a single tool.
That's just the point: Beginners (who are often the ones asking questions like "What scope features should I buy?") don't always have a lab full of equipment. For you and me, sure. But I remember when I was a teenager just starting out... my "bench" consisted of a scope and a multimeter. Period. No 16+ channel logic analyzers, no multiple scopes at the ready. For folks like that, buying their first and (for a while) only scope, I think more channels is more important than a little more bandwidth.

Just my $0.02. YMMV. Standard disclaimers. Etc. There's no obvious correct answer to questions like this, I was trying to genericize the best possible.
 

Online tggzzz

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Re: Oscilloscope bandwidth - is jump from 100MHz to 200 MHz significant?
« Reply #28 on: February 12, 2020, 05:55:13 pm »
You aren't limited to a single tool.
That's just the point: Beginners (who are often the ones asking questions like "What scope features should I buy?") don't always have a lab full of equipment. For you and me, sure. But I remember when I was a teenager just starting out... my "bench" consisted of a scope and a multimeter. Period. No 16+ channel logic analyzers, no multiple scopes at the ready. For folks like that, buying their first and (for a while) only scope, I think more channels is more important than a little more bandwidth.

Hint: look at my .sig!

Anyway, lucky you. I started out with a multimeter, some switches, some LEDs, some potentiometers, and components de-soldered from surplus equipment.

That was sufficient to create this, and later a 6800-based computer with 128 bytes of RAM and a 16-byte ROM made from 16-to-1 multiplexers. I debugged that with a logic analyser made from LEDs and resistors, and used a scope once to check the signal fidelity of the 6800's clock input.

So spare me the lectures about not having much.

Doubly so since a cheap but useful LA can be bought for a few pounds.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
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Offline IDEngineer

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Re: Oscilloscope bandwidth - is jump from 100MHz to 200 MHz significant?
« Reply #29 on: February 12, 2020, 06:10:01 pm »
Hey, this isn't a pissing match. Obviously I wasn't born with a scope in my bassinette. {grin} I was simply pointing out that not everyone has a bench full of gear. True for you at one time, true for me as well, true for everyone. We all start somewhere.

We each have our opinions. We're sharing them here. That's the benefit of a forum like this. Hopefully the OP reads everything, considers his own situation, and makes a (more) informed choice for himself.
 
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Online tggzzz

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Re: Oscilloscope bandwidth - is jump from 100MHz to 200 MHz significant?
« Reply #30 on: February 12, 2020, 06:59:52 pm »
Hey, this isn't a pissing match.

Good.

Quote
Obviously I wasn't born with a scope in my bassinette. {grin} I was simply pointing out that not everyone has a bench full of gear. True for you at one time, true for me as well, true for everyone. We all start somewhere.

We each have our opinions. We're sharing them here. That's the benefit of a forum like this. Hopefully the OP reads everything, considers his own situation, and makes a (more) informed choice for himself.

After 1 year and 11 months, he has probably saved up enough money to buy a cheap LA.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline IDEngineer

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Re: Oscilloscope bandwidth - is jump from 100MHz to 200 MHz significant?
« Reply #31 on: February 12, 2020, 07:27:33 pm »
After 1 year and 11 months, he has probably saved up enough money to buy a cheap LA.
Good point. But such things at such prices were not available when I started out, and depending upon your age perhaps not for you either. {grin}

BTW, I wasn't thinking of a four channel scope as a logic analyzer. I was simply thinking of "signals" in the generic sense, whether analog or digital. A scope can certainly display four digital signals, but a LA cannot display analog signals. So in this sense more channels on a scope are more flexible. If you KNOW you're focusing on digital, maybe you don't need a true scope at all and can save a bunch of money.
 

Online tggzzz

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Re: Oscilloscope bandwidth - is jump from 100MHz to 200 MHz significant?
« Reply #32 on: February 12, 2020, 08:25:00 pm »
After 1 year and 11 months, he has probably saved up enough money to buy a cheap LA.
Good point. But such things at such prices were not available when I started out, and depending upon your age perhaps not for you either. {grin}

BTW, I wasn't thinking of a four channel scope as a logic analyzer. I was simply thinking of "signals" in the generic sense, whether analog or digital. A scope can certainly display four digital signals, but a LA cannot display analog signals. So in this sense more channels on a scope are more flexible. If you KNOW you're focusing on digital, maybe you don't need a true scope at all and can save a bunch of money.

With the exception of photon counting and femtoamp circuits, everything is analogue.

However, those values can be interpreted as digital signals. That's what LAs  and logic inputs do; scopes show you how close the interpretations are to being incorrect. Once you can be sure the interpretation is correct, much simpler and cheaper circuits can process the digital signals.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline sixtimesseven

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Re: Oscilloscope bandwidth - is jump from 100MHz to 200 MHz significant?
« Reply #33 on: February 12, 2020, 09:44:20 pm »
I would not break the bank to go from 100-200MHz.

Most experiments and insights for an beginner into analog could be gained with a 1MHz scope... Just pick your values and frequencies accordingly. E.g. doing the AoE coursebook, did you find something for which you actually need a digital 100MHz scope?

I started with a 30MHz analog Hameg scope which I got for 20 bucks, lasted me 2 years. After that I knew what I would need and bought me a digital scope... That was about seven years ago.... Now I have a 2GHz and a 5GHz scope on my bench, but thats more of a TEA issue :palm:

Anyway, you seem to be kind of in between. You did some stuff with simple entry level solution but you did not yet figure out whats really important to you. Otherwise you would not ask. So if I were you I would wait or buy something used which you can sell again. Those chinese scopes are great bang for the buck but their resale value is terrible...

For digital stuff on the other hand I would recommend a decent USB logic analyzer. I never used digital channels on my scope even when I did have them. If you do Arduino stuff and you do not yet have one, invest here first.
« Last Edit: February 12, 2020, 09:57:26 pm by sixtimesseven »
 

Offline IDEngineer

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Re: Oscilloscope bandwidth - is jump from 100MHz to 200 MHz significant?
« Reply #34 on: February 12, 2020, 10:00:02 pm »
With the exception of photon counting and femtoamp circuits, everything is analogue.
I thought about mentioning that earlier, but decided to not be pedantic. My OCD thanks you for the friendly scratch between the ears!
 


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