Question about analog oscilloscopes vs digital oscilloscopes

[joeqsmith]

Here is another fairly decent article on filtering if interested.   
http://cp.literature.agilent.com/litweb/pdf/5988-8008EN.pdf

Well a high enough sample rate is just one requirement; probably (actually not really probably) a great deal more potentially significant than whether or not the rise-time/bandwidth relationship between two scopes with the same specified -3dB bandwidth differs by 0.35/RT to 0.4 or 0.5/RT 

[GK]

I wrote "a kinda hot thing". And you appear to have missed my following sentence:

"Far from the pinnacle of DSO technology, but a good and well optioned performer in its price bracket".

But that's the point, in terms of real-time performance it simply wasn't. Not in 1998, and a lot less in 2003.

The real-time performance is only one performance parameter. For the going price in 2003, compared to a host of alternative and immediately available offerings for the same $ on loan for evaluation from the distributors that we compared it to, it was exactly what I wrote.
   

Any DSO with a 1GHz analogue bandwidth and an 8GSa/s sample rate is pretty damn "high-end" from a general hobbyist/home lab owners perspective (which was the context of the discussion), be it a 13 year old design or a current production model. 

I guess the various owners of LeCroy LC Series scopes in this group would beg to differ, and these scopes often go for way below the $1k mark (nothing for the broke student, but well into hobbyist territory, which also are pretty much the only people that buy these old scopes today).

I qualified my statement with the word general; obviously in vain  .  If the hobbyist in general had ample opportunity to go out and simply buy a practical 1GHz/8MSa/s DSO for "way below the $1k mark" then the RIGOL threads around here would not run into 100 pages. Everyone would say "go buy a Lecroy XXXXX", not "go buy a RIGOL DS1054Z"!

But this is taking the discussion off track. I simply used the LT344 vs the 7904 to raise a technical contention with tggzzz's assertion that "A DSO and analogue scope with the same bandwidth should indeed show the same signal" as these are "same bandwidth" scopes that I handily have first hand experience with.

But they aren't the same BW scopes. The LT344 doesn't have 500MHz real-time bandwidth, that's merely the analog bandwidth of the front end. A DSO's usable BW however is determined by not just the FE but also the acquisition system BW, and for the LT344 in real-time mode the latter is <250MHz.

Yes they are the same bandwidth scopes - the 500MHz analog bandwidth combined with RIS makes the LT344 a 500MHz scope (with limitations). And FFS I know that the LT344 doesn't have a RTS bandwidth of 500MHz and is Nyquist limited to <=half that. That was the whole freaking point

And yes we really did buy a LT344 "brand new" in 2003. If it was already out of production for a year or two as you claim then it would have been stock that the distributor was keen to shift, which is likely why I recall the favorable price vs performance standpoint. "Obsolete" or not it satisfied our requirements.

That is well and fine, but again, I was just addressing your "Far from the pinnacle of DSO technology, but a good and well optioned performer in its price bracket" statement. In terms of real-time performance for a 500MHz DSO, the LT344 was sub-par already the day it came out. Which makes a comparison as real-time scope against a 500MHz analog scope rather pointless.

The utterly elementary, uncontroversial technical point that I made w.r.t. bandwidth (analogue) and sampling rate and high frequency waveform reproduction has absolutely no contingency whatsoever to the technical caliber (one way or the other) of the LT344 (or any other DSO for that matter) 13 years ago, today, yesterday or at any other point of time in history.
 

[Someone]

Any DSO with a 1GHz analogue bandwidth and an 8GSa/s sample rate is pretty damn "high-end" from a general hobbyist/home lab owners perspective (which was the context of the discussion), be it a 13 year old design or a current production model. 

I guess the various owners of LeCroy LC Series scopes in this group would beg to differ, and these scopes often go for way below the $1k mark (nothing for the broke student, but well into hobbyist territory, which also are pretty much the only people that buy these old scopes today).

I qualified my statement with the word general; obviously in vain  .  If the hobbyist in general had ample opportunity to go out and simply buy a practical 1GHz/8MSa/s DSO for "way below the $1k mark" then the RIGOL threads around here would not run into 100 pages. Everyone would say "go buy a Lecroy XXXXX", not "go buy a RIGOL DS1054Z"!

Mr W seems to be in a special world where Lecroy products are available at huge discounts to the open market, not that they'd share with us how to get these amazing bargains. When us regular people compare eBay or other auction prices the traditional rule of "you get what you pay for" still applies.

[G0HZU]

It seems like every scope thread like this gets trashed by the sausage dog one way or another...

FWIW I still have a Tek 465 on my workbench and it one of only a few select items that never leaves my workbench. My background is RF and I've got some decent (and fairly modern) RF test gear here. But the 40 year old Tek 465 is still very useful when doing quick/casual sanity checks on a modulated RF waveform or a LF waveform that may have issues with RF instability in parts of the waveform.

Wuerstchenhund: Besides, I wouldn't exactly consider clinging to yesteryear's test gear a sign of intelligence 

That probably places me into the moron category because I still have (and use) a 50 year old HP8405A 1GHz vector voltmeter and a 50 year old HP431C/HP478A 10MHz-10GHz RF power meter.

[joeqsmith]

Inappropriate post removed. We don't do provocking eath other on this forum, I don't have time to sort the shit storms out it causes

Simon

[Rupunzell]

Consider this image of Jim Williams, five years later for a moment:
http://www.edn.com/design/analog/4442194/Remembering-Jim-Williams--5-years-later

"Despite Linear Tech making high-performance analog chips, Williams used classic test equipment, like vintage Tektronix oscilloscopes and old HP equipment. That may have been inspired from his work at MIT as a young man, keeping the lab equipment working and designing custom circuits. Paul Grohe, a friend and fellow application engineer at Texas Instruments notes, “Jim’s love of old hardware may be due in part to the fact that you can still fix those old scopes. The new stuff is full of hybrids and proprietary chips that can only be repaired at a factory service center.”


It appears the current generation of electronic folks who are digital/software/code centric simply do not have an appreciation of this analog stuff, appreciation of how rational state of the art test gear designs from the golden era really is and the fact many of these classics are timeless.

Being the owner-user of an hp 8505A vector voltmeter and numerous other vintage test gear that required understanding and ability from the user, not just knowing how to access each and every feature on the display or writing code to drive each and every measurement.
 
Study the working of the hp 4815A vector impedance meter circa 1967.. and be surprised is inside and requirements for accuracy. What can be learned from this classic impedance measurement instrument?
http://people.wallawalla.edu/~rob.frohne/Radio%20Schematics/HP%204815A%20Manual.pdf


Bernice

[Martin.M]

hello Bernice,

I think the friends here will only roll their eyes when we begin to talk about vintage scopes
It will be a good idea to move that to my tread of restoration pictures here in the forum.
We are not modern. 

greetings
Martin

this picture is for remembering to something from yesterday.

[Rupunzell]

After staying away for 6 months, little if anything has changed. It appears each and every time the topic of Analog Real Time CRT based O'scopes -vs- DSO, the same tiresome items appear, same individuals, same attitudes resulting in much of nothing except the war of words, egos and similar. Life is too short for individuals who are learning resistant and entrenched an blinded by their individual myopia. 

Facts are folks, both have their place depending on the specific needs. Using the correct tool for the requirement IS what should be done, not falling into the fantasy one is always better than the other.



Bernice

[Fungus]

Consider this image of Jim Williams, five years later for a moment:
http://www.edn.com/design/analog/4442194/Remembering-Jim-Williams--5-years-later

"Despite Linear Tech making high-performance analog chips, Williams used classic test equipment, like vintage Tektronix oscilloscopes and old HP equipment. That may have been inspired from his work at MIT as a young man, keeping the lab equipment working and designing custom circuits. Paul Grohe, a friend and fellow application engineer at Texas Instruments notes, “Jim’s love of old hardware may be due in part to the fact that you can still fix those old scopes. The new stuff is full of hybrids and proprietary chips that can only be repaired at a factory service center.”

Sure, he would have has a collection of the best vintage equipment, a large collection of probes to go with it, a shed full of spare parts to keep them running, the knowledge to pick the right probe for a job, the knowledge to set the controls properly, the knowledge to interpret the results shown on the screen, etc.

The average electronics newbie? Not so much.

Telling newbies they should be scouring eBay for used Teks? Very bad advice.

[nctnico]

Facts are folks, both have their place depending on the specific needs. Using the correct tool for the requirement IS what should be done, not falling into the fantasy one is always better than the other.

Hint: nobody drives in a model T Ford for their daily commute. Advising young engineers to stick with old and clunky equipment isn't helping them.
I grew up with analog scopes too but using one nowadays? I really see no reason to do so because a DSO can do everything an analog scope can and does it much better.

[Jwalling]

Facts are folks, both have their place depending on the specific needs. Using the correct tool for the requirement IS what should be done, not falling into the fantasy one is always better than the other.

Hint: nobody drives in a model T Ford for their daily commute. Advising young engineers to stick with old and clunky equipment isn't helping them.
I grew up with analog scopes too but using one nowadays? I really see no reason to do so because a DSO can do everything an analog scope can and does it much better.

I'd say "I really see no reason to do so because a DSO can do everything an analog scope can and more and does it much better."

Jay

[G0HZU]

But isn't this a thread about 'looking' at the display so see fluid changes in a waveform? The OP wasn't interested in storage of the waveform.

So this is a human factor question. A traditional analogue scope is a wonderful tool for 'observing' erratically modulated RF waveforms, eg human speech fed into an AM or SSB transmitter for example.

You can get a wonderfully fluid display from pretty much any analogue scope from the last 50-60 years assuming it has enough bandwidth.
I really don't think I would reach for a DSO here if there was an analogue scope next to it. The old CRO will do a very good job here.

If you actually wanted to capture the modulation and post process it rather than just look at it then the analogue scope can't help at all and the DSO would be the tool of choice.

[coppice]

Facts are folks, both have their place depending on the specific needs. Using the correct tool for the requirement IS what should be done, not falling into the fantasy one is always better than the other.

If these older machines are so indispensable for certain applications, I wonder why nobody makes them any more? You would think there would be a market for them.

[nctnico]

But isn't this a thread about 'looking' at the display so see fluid changes in a waveform? The OP wasn't interested in storage of the waveform.

So this is a human factor question. A traditional analogue scope is a wonderful tool for 'observing' erratically modulated RF waveforms, eg human speech fed into an AM or SSB transmitter for example.

If you actually wanted to capture the modulation and post process it rather than just look at it then the analogue scope can't help at all and the DSO would be the tool of choice.

The thing is that just looking at something usually doesn't result in quantifyable measurements. It can look OK but it is really? With a modern DSO you can use the FFT function to look at modulated signals and quantify whether it is within limits or not.

[Wuerstchenhund]

Mr W seems to be in a special world where Lecroy products are available at huge discounts to the open market, not that they'd share with us how to get these amazing bargains.

Only in your mind. In reality, there are lots of good 2nd hand deals out there for those that aren't lazy:

500MHz 4Ch for less than $600:
http://www.ebay.com/itm/LeCroy-Waverunner-LT354M-Oscilloscope-500MHz-1-GS-s-DSO-/231903891732
http://www.ebay.com/itm/LeCroy-Waverunner-LT354M-Oscilloscope-500MHz-1-GS-s-DSO-/231910736019
(BTW: these have 4M sample memory, not 250k as stated in the text!)

There was also one with a few scratches on the protective transparent plastics screen (which isn't difficult to replace) for $460, so pretty much DS1054z money. There's no serial decode but as compensation you get 500MHz BW, 1GSa/s on all channels, and (depending on which software options are enabled, which isn't clear from the text) advanced FFT with up to 1Mpts, jitter/timing analysis, history, statistics and a ton of other math and analysis functions.


1GHz and 8GSa/s for a bit over $1k:
http://www.ebay.com/itm/Lecroy-LC584AL-1GHz-and-8GS-s-in-perfect-working-condition-/272224857602
(BTW, all the software options for that scope can legally be enabled for a few bucks/free, as LeCroy has made them available to hobbyists years ago!)


2GHz, 16GSa/s and 32M sample memory for $1600:
http://www.ebay.com/itm/LeCroy-WavePro-960-Series-2-GHz-4-Channel-Color-LCD-Display-Digital-Oscilloscope-/252392028295


4Ch 500MHz 5GSa/s 24Mpts plus lots of very advanced waveform analysis functions and serial decode for a wide range of standards for less than $1500:
http://www.ebay.com/itm/LECROY-WAVERUNNER-6050A-500MHz-QUAD-5GS-s-DIGITAL-OSCILLOSCOPE-/231965700171
www.ebay.com/itm/LECROY-WAVERUNNER-6050A-500MHz-QUAD-5GS-s-DIGITAL-STORAGE-OSCILLOSCOPE-/231977345364

All within the price range of your average hobbyist gear, with best regards from my "special planet"   


However, in case you were talking about new gear, I guess you missed that I explained, many times btw, that the best way to get bargain prices for kit from any big brand is to go through the manufacturer, talk to their sales staff and start negotiating. Base price for scope plus a range of options thrown in is pretty easy to achieve. There often are also demo scopes which often go for a lot less than 70% of the original price, plus they usually are loaded with options.

If you go through resellers (which want their slice of the cake) then worst case you'll pay list price and best case you get a few bread crumps.

This of course doesn't work everywhere, i.e. countries where the manufacturer has no office, in which case you'd have to go through the importer. If you happen to live at such a place, bad luck.

So no, it's neither "my special world" nor a secret.

When us regular people compare eBay or other auction prices the traditional rule of "you get what you pay for" still applies.

That rule pretty much always applies, but if you can't find any bargains then maybe, just maybe you're simply not looking hard enough? There's no such thing as free lunch, and if you want to find good deals, no matter what brand you're looking into, you have to do your homework.

If you can't be arsed to do that then you'll pay premium. It's as simple as that.

However, all this is unrelated to the topic of this thread. If you truly want to talk about how to find bargains then I'd suggest you start a new thread.

[joeqsmith]

    Pretty much every post I make is intended to provoke members. 

Inappropriate post removed. We don't do provocking eath other on this forum, I don't have time to sort the shit storms out it causes

Simon

[chris_leyson]

Telling newbies they should be scouring eBay for used Teks? Very bad advice

I would second that.
I have two TEK 7854s, I have to re-cap the second one, but for 35 year old kit they're OK they do what I require from a scope but they need constant adjustment or repair. For higher frequency work I have the option of a 7L12 spec-an plugin or I use HP54610 (750 MHz BW) depending if I'm working in the frequency or time domain. Both scopes under sample so they are good for repetative signals but no good at all for capturing single shot transient events. As for FFTs on sampling scopes, OK for a quick look but I can get an extra 30dB dynamic range from a traditional swept analyzer. It all depends on what you want to measure.

[G0HZU]

But isn't this a thread about 'looking' at the display so see fluid changes in a waveform? The OP wasn't interested in storage of the waveform.

So this is a human factor question. A traditional analogue scope is a wonderful tool for 'observing' erratically modulated RF waveforms, eg human speech fed into an AM or SSB transmitter for example.

If you actually wanted to capture the modulation and post process it rather than just look at it then the analogue scope can't help at all and the DSO would be the tool of choice.

The thing is that just looking at something usually doesn't result in quantifyable measurements. It can look OK but it is really? With a modern DSO you can use the FFT function to look at modulated signals and quantify whether it is within limits or not.

You might also want to look in the time domain at the RF envelope to see how an ALC/AMC circuit is performing when fed with human speech.  Sure, it's just a quick/casual 'visual' measurement in real time but the CRO is very good at this.

[Wuerstchenhund]

It seems like every scope thread like this gets trashed by the sausage dog one way or another...

Yeah, I get that for some (mental) oldtimers in here facing reality might hurt. I also get that personal attacks are clearly an easier way to deal with it than facts and arguments (not that this is surprising, after all the world currently has to deal with the fall-out caused by a bunch of people that were completely oblivious to facts and arguments). 

But still, reality is on my side as clearly no-one really makes analog scopes any more, which wouldn't be the case if they were really so useful as the analog scope proponents claim them to be. Maybe manufacturers are all idiots, but I'd guess more likely they know that in the real world they just wouldn't sell.

Wuerstchenhund: Besides, I wouldn't exactly consider clinging to yesteryear's test gear a sign of intelligence 

That probably places me into the moron category because I still have (and use) a 50 year old HP8405A 1GHz vector voltmeter and a 50 year old HP431C/HP478A 10MHz-10GHz RF power meter.

Great for you. So you really wanna suggest that this is a sign of intelligence?

Just to make it clear: there's nothing wrong with using old or even antique test gear if it suits you. But there's a lot wrong in talking beginners into sinking money into archaic pieces of test equipment no-one makes any more despite it's aleged aleged superiority, which is what happens pretty much every time the question re. analog scopes comes up. It's poor advice by any standards, and while it might massage your ego that another 'young one' could be saved to follow the old paths, it only serves to hurt beginners.

[G0HZU]

But still, reality is on my side as clearly no-one really makes analog scopes any more

The thread wasn't about who still makes analogue scopes. It's about how fluid the display is when looking at fast changing waveforms.

Can you suggest an affordable DSO that will provide me with a display as visually fluid as my Tek 465? The Tek 465 cost me about £50 back in the 1990s.

Wuerstchenhund: Besides, I wouldn't exactly consider clinging to yesteryear's test gear a sign of intelligence 

G0HZU:That probably places me into the moron category because I still have (and use) a 50 year old HP8405A 1GHz vector voltmeter and a 50 year old HP431C/HP478A 10MHz-10GHz RF power meter.

Wuerstchenhund: Great for you. So you really wanna suggest that this is a sign of intelligence?

Maybe you need to email the people of low intelligence at Keysight and the various NIST calibration houses that still use the HP478A power sensor (designed in the 1960s) as a transfer standard to calibrate modern RF power meters.

AFAIK some NIST calibration houses use the HP8405A vector voltmeter (designed in 1965?)  to cross check various atomic frequency standards over time. They may use something newer today but up until recently the old VVM was a classic tool for stuff like this. I bought it to measure/verify negative impedances for some study work but maybe you also need to email the people who use 1960s VVM technology (to cross check atomic standards) to tell them how dumb they are.

[tggzzz]

Facts are folks, both have their place depending on the specific needs. Using the correct tool for the requirement IS what should be done, not falling into the fantasy one is always better than the other.

Yup. Dogma is simplistic and annoying.

The only change I would make is to say "using the best available tool for the requirement". A working scope in the hand is worth two on ebay

[nctnico]

But isn't this a thread about 'looking' at the display so see fluid changes in a waveform? The OP wasn't interested in storage of the waveform.

So this is a human factor question. A traditional analogue scope is a wonderful tool for 'observing' erratically modulated RF waveforms, eg human speech fed into an AM or SSB transmitter for example.

If you actually wanted to capture the modulation and post process it rather than just look at it then the analogue scope can't help at all and the DSO would be the tool of choice.

The thing is that just looking at something usually doesn't result in quantifyable measurements. It can look OK but it is really? With a modern DSO you can use the FFT function to look at modulated signals and quantify whether it is within limits or not.

You might also want to look in the time domain at the RF envelope to see how an ALC/AMC circuit is performing when fed with human speech.  Sure, it's just a quick/casual 'visual' measurement in real time but the CRO is very good at this.

If I may interpret 'seeing fluid changes' as slow phosphor response then I have to say a DSO can do the same by adjusting the persistence time.

[Fungus]

500MHz 4Ch for less than $600:

+$300 shipping...

4Ch 500MHz 5GSa/s 24Mpts plus lots of very advanced waveform analysis functions and serial decode for a wide range of standards for less than $1500:

+$683.63 shipping...


(And let's hope customs don't spot it or it'll be 25% more on price+shipping)

[nctnico]

The shipping costs can be reduced if the seller is willing to use USPS. Otherwise a forwarding service can be cheaper.

[Wuerstchenhund]

500MHz 4Ch for less than $600:

+$300 shipping...

4Ch 500MHz 5GSa/s 24Mpts plus lots of very advanced waveform analysis functions and serial decode for a wide range of standards for less than $1500:

+$683.63 shipping...


(And let's hope customs don't spot it or it'll be 25% more on price+shipping)

These might be the shipping costs to your place (wherever that might be, since you didn't state location), not to everywhere. As to customs, here in the UK I pay 'just' 20%, not 25%, which is because VAT rates vary by country.

If you buy from abroad then shipping and customs need considering. If you buy products made abroad then you pay at least some of the cost to get the item into your country through the inflated sales price. That's just how it is with international trading.

Besides, it shouldn't be surprising that US buyers get some of the best prices, because this is pretty much true for the majority of technical goods and has been this way for a long time. If you don't live in the US then in generally you'll pay more, that's simply how it is.