Analog Oscilloscope vs. Digital Oscilloscope

[djcrunkmix]

Hi guys,

I am a novice electronics enthusiast. After watching Dave's review of the good ol' Tektronix 2225 50Mhz scope here:

 

I thought, I'd get myself an analog scope. I bought one from eBay for $250 USD. The model I found was slightly more advanced - Tektronix 2440 w/300Mhz bandwidth.

I was a little bit disappointed with the fact that I cannot really "properly" learn how to use an oscilloscope without getting a really old school one like Tek 2225. To my surprise, the Tek 2440 is a digital scope with storage capabilities and tons of math functions.

My question now is how do I view the tracing (from left to right) of the cursor? Is it not available in digital scopes? When I switch my horizontal axis to larger time scales, I get something like this:



Triggering is in "Roll" mode.

Is this how digital oscopes work? They seem to have a memory buffer where the waveform gets saved and displayed. Do analog scopes also have a buffer?

I think I am going to sell this one and get the exact model as Dave has recommended...i.e. Tektronix 2225. I really like the tracing of the cursor...

Thanks for the advice

Neil

[c4757p]

Switch the trigger mode out of "roll", to "auto". Roll just displays the signal rolling out of the right side of the screen with no triggering. Auto will lock the signal to a trigger point so it stands still.

Yes, that is how digital scopes work. The signal is read into a buffer, then displayed digitally. Analog scopes do not have a buffer (except for analog storage oscilloscopes, which are rare). They display the signal in literal real time - the signal pretty much just goes through an amplifier right to the vertical deflection plates of the CRT. (If you're curious, look up a schematic for one of the very old, simple vacuum tube-based scopes like the Heathkit ones. The circuits are very basic and you can see the pattern: Signal -> Amplifier -> Vertical deflection. Ramp generator -> Amplifier -> Horizontal deflection.)

FWIW, you were only off by 0.2% on your model number!  I have a 2445A and it's a quite sophisticated analog scope.

[c4757p]

I think I am going to sell this one and get the exact model as Dave has recommended...i.e. Tektronix 2225. I really like the tracing of the cursor...

If you're in the $250 range, I recommend the 2400 series of analog scopes - shame they had to make the model numbers so similar  You get higher bandwidth plus some useful "analog+digital" features - mine has movable cursors for taking measurements, automatic trigger level, a full automatic configure like the "auto" button on many newer digital scopes (which you should not be using  ), a digital frequency counter (this is optional, though), and a few other things that make it just as easy to use as a digital scope.

[djcrunkmix]

Switch the trigger mode out of "roll", to "auto". Roll just displays the signal rolling out of the right side of the screen with no triggering. Auto will lock the signal to a trigger point so it stands still.

Yes, that is how digital scopes work. The signal is read into a buffer, then displayed digitally. Analog scopes do not have a buffer (except for analog storage oscilloscopes, which are rare). They display the signal in literal real time - the signal pretty much just goes through an amplifier right to the vertical deflection plates of the CRT. (If you're curious, look up a schematic for one of the very old, simple vacuum tube-based scopes like the Heathkit ones. The circuits are very basic and you can see the pattern: Signal -> Amplifier -> Vertical deflection. Ramp generator -> Amplifier -> Horizontal deflection.)

FWIW, you were only off by 0.2% on your model number!  I have a 2445A and it's a quite sophisticated analog scope.

LOL..yes. I was like, that looks older than the internet. Must be analog. Close enough model number... 

I think I am going to sell this one and get the exact model as Dave has recommended...i.e. Tektronix 2225. I really like the tracing of the cursor...

If you're in the $250 range, I recommend the 2400 series of analog scopes - shame they had to make the model numbers so similar  You get higher bandwidth plus some useful "analog+digital" features - mine has movable cursors for taking measurements, automatic trigger level, a full automatic configure like the "auto" button on many newer digital scopes (which you should not be using  ), a digital frequency counter (this is optional, though), and a few other things that make it just as easy to use as a digital scope.

Thanks I shall look into it. Also, I love the facepalm icon:   

[c4757p]

The facepalm icon is very useful here - you're in electronics now. Give it a couple weeks and you'll have a permanent palm print in your forehead. Not to mention a few soldering iron marks 

[c4757p]

LOL..yes. I was like, that looks older than the internet. Must be analog.

Look at some mid-late 90s test equipment - you'll be surprised how "old" a lot of the equipment looks to a new eye. A lot of the newer stylings are quite recent.

[Spawn]

I got a Tek 2221A 100MHz digital storage oscilloscope, with cursor to measure various things, you can turn off its storage mode and use it as normal analog oscilloscope. Unit itself is same size as a 2225.

Here a picture of its console to give you a idea (the picture is not mine)

[c4757p]

Looks nice. I'd miss my dual timebase and four channels though.

[codeboy2k]

found a 2445A for $160 , including shipping. 

http://www.ebay.ca/itm/Tektronix-2445A-Oscilloscope-/251179698826?pt=LH_DefaultDomain_0&hash=item3a7b7a0a8a

Needs a little work though...

[BravoV]

Needs a little work though...

Haha.. almost got heart attack seeing the pictures of that poor thing. 

Yeah.. little work in this case here is not to fix it but to desolder the precious unobtainium U800 chip that is still sticking at the main A1 board, presumably not toasted of course.   

[EEVblog]

As someone else mentioned, roll mode is not the correct mode to use for general digital storage scope operation.
As you found out, you have a purely digital scope with the 2440, not an analog scope.
There are "combi" scopes that have switchable true analog and digital storage modes, but they aren't that common (the 2221 shown is a good example), and sometimes not obvious! Check out the Hameg 1507 below and try and figure out what type it is...

Nothing special about the 2225, apart from the 500uV/div mode. Any basic analog scope will let you learn the basic.

Dave.

[Hydrawerk]

I got a Tek 2221A 100MHz digital storage oscilloscope, with cursor to measure various things, you can turn off its storage mode and use it as normal analog oscilloscope. Unit itself is same size as a 2225.

Here a picture of its console to give you a idea (the picture is not mine)

I would miss the autoset button.

[c4757p]

The what? Why?

[Wuerstchenhund]

I was a little bit disappointed with the fact that I cannot really "properly" learn how to use an oscilloscope without getting a really old school one like Tek 2225.

Don't know why you think this is the case but that's not true. While it's certainly not a bad way to get introduced to scopes through an analogue scope, it's not the only way. I have learnt on both analogue scopes (because this was the predominant type of scope at that time) and DSOs, and I say You can learn the basics with any decent DSO as well (just keep the hands off from the automatic functions!), and once you're done with the basics you may want to learn the more advanced analytical stuff and then an old analoge scope won't cut it anyways.

To my surprise, the Tek 2440 is a digital scope with storage capabilities and tons of math functions.

Nice scope! 500MSa/s are a bit low but as a first scope this should do well.

I think I am going to sell this one and get the exact model as Dave has recommended...i.e. Tektronix 2225. I really like the tracing of the cursor...

I will certainly get burned for saying this but...

You apparently got a very nice 300MHz DSO there, and now that you have it I think it would be silly to sell it just to get an old analog banger 'for learning'. It's like passing your driving test and then getting a hearse to 'learn the basics' before driving a car. At the end of the day, a scope is a tool, and to make use of this tool you need to understand what it does and learn how to use it. Analog scopes were great in their days (and it certainly doesn't hurt to have one as a secondary scope if that's what you want), but their time is gone. And while knowledge in handling an analoge scope is not a bad thing, the main aim for you as a starter should be to learn the basics. And you can do that as well on your scope.

[djcrunkmix]

Thanks for the advice. I think I am going to buy another one One can never have too many scopes. 

[Hydrawerk]

The what? Why?

"Autoset" button can be found on Dave's HM1507 scope above.

[c4757p]

Thanks for the advice. I think I am going to buy another one One can never have too many scopes. 

I've decided to stop at two before I go completely oscilloscope-crazy.

The what? Why?

"Autoset" button can be found on Dave's HM1507 scope above.

And on pretty much every other scope with any digital anything in it. I'm not convinced it has a purpose, though...

[Lukas]

Autoset might be of limited usefulness, indeed. Although, I once had a german Grundig MO53 (analog scope with digitally controlled timebase) which had an automatic timebase setting which set the timebase to display a few cycles in less than one second (!). I haven't encountered any DSO which this feature, despite it would only be a bit of software.

[c4757p]

I have one use for the autoset on my Tek 2445A - quickly getting out of weird modes. I'll admit to not being fully aware of every setting of the dual timebase and digital counter/timer module, and a quick press of "auto" cancels all of them.

[codeboy2k]

I'm not sure why so many people are against the autoset buttons found on most every digital scope these days.

I started in the late 60's /early 70's using simple scopes made with vacuum tubes, so I am certainly no beginner and know my way around the scopes settings, in other words, I know how to find a trace.

But the autoset in my opinion is just a time saver for me, when I switch from one signal to another that may be two very different signals.

It can make all the same decisions I can make regarding timebase, volts/div, offset, and trigger level, and much faster than me to get a stable image.

So I use it as a starting point, almost always. It's useful. 

Perhaps a beginner should hook the autoset button to a high-voltage spark coil under their seat cushion, until they have learned the other settings.
But I'm an old timer, I don't have much life left in me, I can use all the seconds I have been given

[c4757p]

I find it un-intuitive, in that if I press it, I don't know what I'm looking at. I have to take time to read off the scale indicators to know the difference between a 100uV signal and a 500mV signal, and between 1 MHz and 1 kHz. If I scale the signal manually, I quickly get a feel for the magnitude of the scales based on how much I had to turn the knobs.

If I have multiple different signals that I will be switching between quickly, I connect them to separate channels and just enable/disable the channels.

[EEVblog]

But I'm an old timer, I don't have much life left in me, I can use all the seconds I have been given

But don't forget to enjoy it!
The auto-set button has no joy...

Dave.

[Wuerstchenhund]

I'm not sure why so many people are against the autoset buttons found on most every digital scope these days.

Probably because when autoset first came up on some more advanced analogue scopes it was limited and often turned out to be no help. While the trace would generally end up somewhere on the screen the settings choosen by autoset often didn't lead to a useful display. And because it was slow it didn't really save time, and you had to press other buttons to find out what settings have been choosen so that you knew what you're looking at. It's not quite the same on somewhat modern DSO, where autoset acts relatively fast and almost always chooses at least very good settings, and on most DSOs the chosen parameters are already indicated on the screen so with a quick look you know what you're looking at.

I guess it's a similar thing as analogue vs digital scopes, where some are against DSOs because the first scope generations came with very low sample rates and memory, and were only good for repetitive signals and useless for finding glitches. That's probably also the reason why common belief is you can only learn using a scope properly with an analogue one.

I started in the late 60's /early 70's using simple scopes made with vacuum tubes, so I am certainly no beginner and know my way around the scopes settings, in other words, I know how to find a trace.

But the autoset in my opinion is just a time saver for me, when I switch from one signal to another that may be two very different signals.

Same here (except that I'm slightly younger  ). I know how to set my scopes up correctly but autoset is a time saver, especially with unknown signals.

[PA4TIM]

I use auto to reset the scope after setups that involved lots of settings, but never when measuring.
I had a 2445A, i gave it away when I got a DS1102E and two Tek 7000 scopes.
After the DS1102 I rather hated DSOs and it retired to a corner of the shack using only anlog scopes. But without the 2445A I missed cursormode so I ended up with a 350 MHz Hameg DSO and this is now the scope I use 99% of the time. It has taken me one year of therapy, but now I am able to tell ; "if I had to choose between analog of digital I would choose digital" 

[Martin.M]

hello friends,



this is a oftenly used analog scope of my collection. For faster moments there is a 7104 also...
and most used are still the glowing beauties, like 556, 549 and a little 323 for outdoor. 422 is also oftenly running.
No, I don`t need DSO.

greetings
Martin