Question about analog oscilloscopes vs digital oscilloscopes

[tggzzz]

My point to Wuerstchenhund (or rather, rubbing his nose in it!) in my previous post is that it's completely wrong to push a DSO on the basis of the precision of its measurements.

Precisely. Overstated claims in one area bring into question the validity of claims in other areas.

Use the best available tool for the job.

[Martin.M]

when the space is not enough to use an DSO + RMS Multimeter, use simply an analog scope 

[tggzzz]

i already have a decent digital scope on its way, Im just trying to build my learning lab without having to spend too much. So if an analog scope is useless when i have a decent DSO than i can cross it out on the list so it can go towards getting other things instead.

Don't trust any tool too much. Use it, ensuring you work out where it is lying to you - and whether such lies are of any significant to you.

Only after you have determined that the tools at your disposal are inadequate for your jobs, will you be in a position to know what you need next.

Fundamentally, if you have to question the need for a tool, then you have already answered the question (you don't need it).

[GK]

Analog oscilloscope technology, for all sakes and purposes, is as dead as the dodo, so some of the more strident pro-DSO zeal that invariably infects these threads doesn't come across as much less  than anything posted by the other side.

An analog scope has been my traditional go-to instrument for any RF work (from LF to ~50 MHz) due to the freedom from aliasing and the ability to display AM and SSB modulation envelopes unmolested. It's taken DSO technology a long while to match the performance of analog in this regard, so if you're a HAM or a radio enthusiast procrastinating over which kind of secondhand shack scope to blow your limited budget on, the question of analog versus digital is still relevant. Just for example a $50 20MHz analog scope would serve you better for AM radio restoration than, say, Rigol DS1102CA.

Suppose you want to view the SSB modulation envelope of a 20m (14 MHz) transmitter. Your modulation frequency is 400Hz. To view two full cycles (a period of 5ms) on the scope screen you'll need a horizontal timebase setting of 500uS/Div. To satisfy Nyquist, to resolve the 14MHz carrier without aliasing the sample rate must be 28M samples per second. That requires a memory depth of 5ms / (1/28M) = 140,000 points. Very few DSO boat anchors will do this.

I've got a Rigol DS1202CA (200MHz, 2Gsa). It's completely useless for this kind of work (but that is OK, because this isn't what I bought it for). It's supposed to have a memory depth of 10k-points in single channel mode and 5k-points in dual-channel mode. Until this even I hadn't ever bothered to verify this claimed spec, but this evening just out of curiosity I tabulated the displayed sample rate for each timebase setting and calculated the memory points. This is in single channel mode and maybe I'm missing something because at no setting do I get 10k and it only does 5k on the lowest three decades.



Some Tek 545B goodness for comparison  :


 

[tggzzz]

Suppose you want to view the SSB modulation envelope of a 20m (14 MHz) transmitter. Your modulation frequency is 400Hz. To view two full cycles (a period of 5ms) on the scope screen you'll need a horizontal timebase setting of 500uS/Div. To satisfy Nyquist, to resolve the 14MHz carrier without aliasing the sample rate must be 28M samples per second.

Err. No. Provided you have a good sampler, you could sample that at 800Hz.

How well would your DSO handle a QAM constellation diagram, especially with AGWN?

Some analogue scopes are famed for their overload performance, which is absolutely critical when looking at settling times. See Jim Williams for examples, of course!

[Martin.M]

you mean scopes like this?

[GK]

Suppose you want to view the SSB modulation envelope of a 20m (14 MHz) transmitter. Your modulation frequency is 400Hz. To view two full cycles (a period of 5ms) on the scope screen you'll need a horizontal timebase setting of 500uS/Div. To satisfy Nyquist, to resolve the 14MHz carrier without aliasing the sample rate must be 28M samples per second.

Err. No. Provided you have a good sampler, you could sample that at 800Hz.

Clearly not what I was talking about. And no, the DS1*02CA series and a great many other DSOs do not have a "good sampler".

How the Rigol renders a 400Hz 100% AM modulated 20m carrier, the only difference between the two screen shots is a slight variation in carrier frequency. If you carefully adjust the carrier frequency you can actually get a pretty reasonable looking static modulation envelope displayed, but that's a contrived test condition that has little relevance to real-world usage.



EDIT: Ignore the frequency counter that's showing ~10MHz - it doesn't work properly at this timebase-to-frequency ratio.

[System Error Message]

Typical engineer handwriting

Thanks though for the info, so it seems AM Radio still prefers analog scopes. I dont plan on doing AM or old TV radio but its good to know applications that prefer analog scopes.

[vk6zgo]

what i want to do is measure variances in a DC supply voltage when under various different loads*. I want to learn to build an ultra stable DC PSU. One of the common causes of failures for something like a router (such as router freezing or not working) is almost always the PSU.

*Rather than sitting there,waiting for a  random different load to cause a variance,the logical thing is to switch in  various loads,in a controlled manner while your DSO,CRO,or whatever is already operating.

OK,you might miss the "one in a million " occurrence,but you will pick up the vast majority of problems.

[nctnico]

Suppose you want to view the SSB modulation envelope of a 20m (14 MHz) transmitter. Your modulation frequency is 400Hz. To view two full cycles (a period of 5ms) on the scope screen you'll need a horizontal timebase setting of 500uS/Div. To satisfy Nyquist, to resolve the 14MHz carrier without aliasing the sample rate must be 28M samples per second. That requires a memory depth of 5ms / (1/28M) = 140,000 points. Very few DSO boat anchors will do this.

Hint: peak detect

[GK]

Thanks though for the info, so it seems AM Radio still prefers analog scopes. I dont plan on doing AM or old TV radio but its good to know applications that prefer analog scopes.

Just to be clear this is not outside the capabilities of DSO technology; just not the kind of DSO you're likely to pick up for the price of an old analogue boat anchor.
 

[Martin.M]

the old boatanchor scopes have still their place.

When you make a mistake and put the hook in the high voltage you will understand that is sometimes better to use a glowing input 
Of coarse the time of them is gone, but they are still useful and can help. I am collecting them, so I love to work with a 556 ...

There are some specialities where modern DSO can get a problem to follow, by example: when your 545B is plugged with it`s 1A7 it will read 10µV/div. I want to see a normal DSO what can do that also.

greetings
Martin

[GK]

Suppose you want to view the SSB modulation envelope of a 20m (14 MHz) transmitter. Your modulation frequency is 400Hz. To view two full cycles (a period of 5ms) on the scope screen you'll need a horizontal timebase setting of 500uS/Div. To satisfy Nyquist, to resolve the 14MHz carrier without aliasing the sample rate must be 28M samples per second. That requires a memory depth of 5ms / (1/28M) = 140,000 points. Very few DSO boat anchors will do this.

Hint: peak detect

If the DSO has peak detect, yes, that may help. Incidentally, since I've never used my Rigol for this kind of thing I've never bothered to check/test if it has properly functioning peak detect. I just checked and it does and I am genuinely surprised at how well it works at resolving the above described modulation envelope, compared to what I've seen of other DSOs. Although the display update rate is crap and the resultant display is no where near as pretty when the modulation source is varying in amplitude rather than static.

 

[Gyro]

i already have a decent digital scope on its way, Im just trying to build my learning lab without having to spend too much. So if an analog scope is useless when i have a decent DSO than i can cross it out on the list so it can go towards getting other things instead.

Other than the DSO and stuff i already have (that includes bench PSU) the stuff left on my list was
analog scope
bench DMM
rigol DP832
analog discovery
a reflow soldering station like Dave mentioned in his tutorial video.

Essentially none of these i need immediately for starting up. If there is no use for an analog oscilloscope when i already have a decent scope (which costed about $1000) than i can cross it out my list and get something else on my list instead that would be useful or maybe buy more capacitors for fun.

Ah, ok, I hadn't realised that you already had a (rather good sounding) DSO on the way. In that case you probably owe yourself a boatanchor Analogue scope anyway, firstly to see why it always provokes such heated argument, and secondly for the sheer joy of owning and using one.

Clearly you should keep your spending priorities straight, but I wouldn't let that put you off keeping an eye out for a real bargain. As someone said, it's always useful to have a second scope for helping to fix the other one. From all your questions it's clear to me that you're desperately trying to find an excuse to get one anyway! 

If you have both, then you'll be ideally placed to take full part in the next heated debate... there should be another one coming along in about 3-4 weeks. 

[System Error Message]

Well there are a lot of good advice and links in this thread. At least now i can totally ditch ebay which is very overpriced in the UK and very fake too. I havent used ebay for many months but since not only is the quality or legitimacy worrying but also they tend to be overpriced compared to other places. I even found electronics components from china much cheaper than ebay so while the quality and source may be the same at least the price is much less.

Definitely looking forward to trying things and making sure i only blow up what im working on and not the scope or test meters. Is it safe to blow up electrolytic capacitors?

[Fungus]

Is it safe to blow up electrolytic capacitors?

It all depends on the size of the capacitor, the over-voltage, the available current...

You probably won't die, if that's what you mean. Not unless you have a heart condition and die of fright from the bang. OTOH it can be really unpleasant; they make huge clouds of stink and fill the air with tiny bits of electrolyte-soaked paper that slowly settles all over everything in the room.

If you ever manage to blow one indoors by accident you'll be very careful around electrolytics after that - guaranteed!

Edit: If the metal case hit you in the eye it could be nasty. I've seen a dent in a wall from quite a small capacitor that exploded.

[nctnico]

Is it safe to blow up electrolytic capacitors?

No. Blowing stuff up can go horribly wrong.

[FlyingHacker]

Blowing up a selenium rectifier will leave your room smelling like garlic for weeks if not months.

[joeqsmith]

Is it safe to blow up electrolytic capacitors?

 

[guido]

I've done that once with a tiny cap, which was in the wrong way around. Then you never do that again and check >three times if all is in the right way around. Now that you're starting to ask questions on blowing stuff up, i'm wondering how long your new scope will last.

[robert_]

Blowing up a selenium rectifier will leave your room smelling like garlic for weeks if not months.

What smells like garlic is mostly SeH2, which happens to be very toxic and it is best avoided to produce any of that (same applies to any Se compound).

5: Analog scopes fill up empty spaces nicely. If you think your workbench is much too big then analog is the way to go. DSOs are simply too small for this and not very stackable.

Depends on the DSO. Modern low-end stuff is, but anything else is not exactly small. Both old and new, as soon as it gets anywhere mid-range or up, its gonna be large (which is good as it means a large display) and loud.

6. Most analog scopes dont have a fan, and if they do its not as hugely loud.
Now, my HP 1980B combines both analog and digital resulting in a device that is both analog and also hugely loud as it does have that 60mm 3-phase fan to blow out 200W of heat produced by approx. 2 square meters of PCB area packed incredibly full of THT components. It also has the digitizer option that can fill 512 poilts of storage in about 5 seconds with sequential sampling, or even single-shot at a few kS/s.
Also it is the first analog scope to feature an incredibly crappy user interface, only to be exceeded in unusability by the first HP greenscreen DSO.

[Jwalling]

Is it safe to blow up electrolytic capacitors?

Aluminum cans are not so bad (depending on the size, of course) but wear eye protection! Tantalums on the other hand, get out the blast shield and fire extinguisher! 

Jay

[robert_]

Worst component to blow up IMO: these golden-coloured aluminium case 50-100W resistors. Resistance wire is wound around a ceramic rod, put into the thickwalled aluminium case and potted with some bakelite-like substance, which decomposed under overload and produces a very high pressure, until something BAD happens.
At work we have the ceramic rod from one of these solidly embedded in the ceiling, missed someones head by just a few cm.

Smelliest part: a can of expired surströmming in a campfire. Apart from that, polymer electrolytic capacitors (such as sanyo SEP). Small but stinks at least 26db worse than any regular electrolytic.

[Jwalling]

Worst component to blow up IMO: these golden-coloured aluminium case 50-100W resistors. Resistance wire is wound around a ceramic rod, put into the thickwalled aluminium case and potted with some bakelite-like substance, which decomposed under overload and produces a very high pressure, until something BAD happens.
At work we have the ceramic rod from one of these solidly embedded in the ceiling, missed someones head by just a few cm.

I must admit that I've never seen one of those blow up! IIRC Dale made those, yes?

Jay

[System Error Message]

you guys are so enthusiastic, even more active than the computer networking forums lol, especially when it comes to tools, designs and blowing things up. Next thing we'll be discussing about buying uranium from amazon and enriching it.