New Analog Scopes? - Page 1
Forum section: electronics / testgear

author: nicknails
author_rank: Regular Contributor
timestamp: March 12, 2013, 12:16:43 am
content: Does anyone still make decent analog scopes? I am looking for a couple new scopes at my work and I prefer analog scopes, mostly because of they're triggering. I have a couple Rigol cheapies and the triggering annoy that crap out of me. It seems that no one makes anything decent with storage capabilities anymore. I have 3 old analog Hameg's that I like, but they're starting to crap out on me.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 12, 2013, 12:44:11 am
content: QuoteHuh?Pretty much any digital scope, however cheap and crappy has better storage capability than any analogue storage scope ever made...If you want a good analogue scope, look for a used Tek 2465A/B - one of the best analogue scopes ever made.

author: c4757p
author_rank: Super Contributor
timestamp: March 12, 2013, 12:45:58 am
content: Quote from: mikeselectricstuff on March 12, 2013, 12:44:11 amSeconded with enthusiasm.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 12, 2013, 12:52:53 am
content: Holy crap - just looked at RS and they have 17 models of analogue scopes from 3 manufacturers - a couple over a grand!Who on earth buys this stuff nowadays?

author: c4757p
author_rank: Super Contributor
timestamp: March 12, 2013, 01:01:56 am
content: Maybe some schools want to keep a few CROs around. Probably cheaper to just pay for the thing new than to take the chance that a used one is broken and will need expensive troubleshooting time and repairs.

author: Hydrawerk
author_rank: Super Contributor
timestamp: March 12, 2013, 01:09:35 am
content: GW Instek still produces decent analog scopes, but I would not buy any analog scope today.http://www.gwinstek.com/en/product/productdetail.aspx?pid=3&mid=6&id=60

author: nicknails
author_rank: Regular Contributor
timestamp: March 12, 2013, 02:02:41 pm
content: Mike, I meant analog scopes with storage capabilities. I know every DSO on the market has better storage capabilities than anything analog.I've always used analog and the few DSO's that I've used totally suck at triggering. Maybe it's because we have bottom rung Rigols.On a side note, any good guides out there for refurbishing Hameg scopes? If I can clean or replace the pots, they'll probably work much better.

author: Nack486
author_rank: Contributor
timestamp: March 12, 2013, 02:18:11 pm
content: Quote from: Hydrawerk on March 12, 2013, 01:09:35 amWe have the 6520 in the school lab. Haven't gotten the chance to work with it myself but it seemed decent (well, at least compared to the other scopes we have...). The question is, again, why would you need an analogue oscilloscope these days? I understand using analogue multimeters (you can see peaks) but you got me thinking if there's an actual advantage using the old scopes.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 12, 2013, 02:23:54 pm
content: Quote from: nicknails on March 12, 2013, 02:02:41 pmSucked inI what way ?Triggering isn't something that's hard to do so not sure what the problem would be. Digital scopes generally have a lot more options, like pulse width etc.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: March 12, 2013, 04:25:10 pm
content: Quote from: nicknails on March 12, 2013, 02:02:41 pmI don't know what DSOs you have used but the DSOs I work with have triggering capabilities far beyond any analog scope.Maybe the DSOs you have used where just shit?

author: PaulAm
author_rank: Frequent Contributor
timestamp: March 12, 2013, 05:14:32 pm
content: If youreallyneed an analog storage scope, Tek 7934s were in production to 2000, so they're not that far out of date.Given all of the neat tricks you can do with a DSO with a decent sample memory, that is really outmoded tech though.

author: nctnico
author_rank: Super Contributor
timestamp: March 12, 2013, 06:30:10 pm
content: Quote from: mikeselectricstuff on March 12, 2013, 12:44:11 amThose are getting really old. Better look for something more modern like the Iwatsu SS-7847A (Lecroy LA314H).

author: Tepe
author_rank: Frequent Contributor
timestamp: March 12, 2013, 06:55:20 pm
content: Quote from: nctnico on March 12, 2013, 06:30:10 pmTEquipment has it for a mere $12319.50

author: Anquietas
author_rank: Regular Contributor
timestamp: March 12, 2013, 10:11:02 pm
content: Quote from: Tepe on March 12, 2013, 06:55:20 pmWho spends that much money? I would assume that adapting a working system to a new scope is much less costly than getting a "new" old one to fit into the prefabricated slot (all things considered) in the system...

author: GK
author_rank: Super Contributor
timestamp: March 12, 2013, 11:28:28 pm
content: Quote from: Nack486 on March 12, 2013, 02:18:11 pmTry looking at an audio-modulated RF envelope on a typical DSO for a start.

author: Hydrawerk
author_rank: Super Contributor
timestamp: March 13, 2013, 01:21:38 am
content: typical DSO=TDS220Yes, but today we have better digital phospor scopes with 1 000 000 waveforms per second (DSOX3000 series). There will be no problem with looking at audio-modulated RF envelope.

author: nctnico
author_rank: Super Contributor
timestamp: March 13, 2013, 01:34:49 am
content: Quote from: Tepe on March 12, 2013, 06:55:20 pmI sold mine for € 475,- a couple of years ago.@Hydrawerk: The TDS200 series is so crappy that anyone mentioning it should get banned for a week!

author: w2aew
author_rank: Super Contributor
timestamp: March 13, 2013, 01:38:06 am
content: Quote from: Hydrawerk on March 13, 2013, 01:21:38 amThe problem with many DSOs looking at an audio modulated RF envelope has little to do with waveform update rate - it has to do with the aliasing / under-sampling of the carrier when the horizontal scale (sweep speed) is slowed enough to clearly observe the audio patterns. Some DSOs give you ability to change the sample mode to +/-peak to try to compensate.Still, an analog scope does excel in this application.

author: Hydrawerk
author_rank: Super Contributor
timestamp: March 17, 2013, 02:04:56 pm
content: Metrix (Chauvin Arnoux) produces some decent oscilloscopes, but I have never used them. The older Hamegs looked better...http://www.chauvin-arnoux.com/display.asp?1917

author: Hydrawerk
author_rank: Super Contributor
timestamp: March 17, 2013, 02:17:01 pm
content: Unfortunately, this machine is not produced anymore.

author: Lukas
author_rank: Frequent Contributor
timestamp: March 17, 2013, 04:25:56 pm
content: Quote from: w2aew on March 13, 2013, 01:38:06 amThis ain't a problem if you implement sampling at low sampling rates right. Let's assume that the ADC always runs at full sample rate. At low sampling rates you have many superfluous samples. What to with them?1. just take any nth and discard the others and get aliasing2. store min and max and loose statistical information3. average: brings down the noise level, but you loose high frequency content4. take a random sample: you don't get aliasing and retain statistical information (where the signal spent a certain amount of time)HP published an article on this in one HP Journal issue, don't remember which.Anyway you don't have to care about this when using a recent DSO such as the Agilent DSOX series, which give you an analog-like display.Concerning analog scopes:If you need high performance and flexibility and don't have a massive amount of money, a used analog scope is pretty much the sole option. I paid less that 100€ for my tek 7834 with Plugins. With a bit of adjustment (reduced scan, fast storage mode) you get 500MHz single shot bandwidth. The other extreme is the 7a22 plugin with gives you sensitivity down to 10µV/div at a bw of 1MHz. That's unbeatable value for money, even it would have cost 1000€.

author: Gunb
author_rank: Regular Contributor
timestamp: March 17, 2013, 11:19:00 pm
content: Quote from: mikeselectricstuff on March 12, 2013, 12:52:53 amThere're still reasons for analog scopes, especially where storage is not needed. For audio measures I prefer to use my good old Hameg 407 combiscope with 40MHz bandwidth. The cathode ray is faster than most digital scopes, so wfm/s isn't an issue. Did you try to see an AM on a scope with low wfm/s? No problem with analog scopes. So, I would miss it if it wouldn't be on my desk, although I've got 3 digital scopes, too.Kind rgdsGunb

author: Gunb
author_rank: Regular Contributor
timestamp: March 17, 2013, 11:22:03 pm
content: Quote from: Lukas on March 17, 2013, 04:25:56 pmI agree, and 1000,-€ can be less money for what you might get, even for a used analog scope.RgdsGunb

author: zaoka
author_rank: Frequent Contributor
timestamp: March 18, 2013, 12:50:26 am
content: http://www.testequipmentdepot.com/hameg/oscilloscopes/hm400.htm

author: EEVblog
author_rank: Unknown
timestamp: March 18, 2013, 02:12:57 am
content: Quote from: nicknails on March 12, 2013, 12:16:43 amHameg make "combi" analog and digital storage scopes. So why not just get a modern digital scope when you need storage, and just a regular analog when you need/want analog?And why are analog scope superior to digital scope when it comes to triggering?Dave.

author: EEVblog
author_rank: Unknown
timestamp: March 18, 2013, 02:15:16 am
content: Quote from: Hydrawerk on March 13, 2013, 01:21:38 amYes,20 YEARS AGO!A "typical" DSO has advanced just a tad since then...Dave.

author: Gunb
author_rank: Regular Contributor
timestamp: March 18, 2013, 09:43:43 am
content: Quote from: EEVblog on March 18, 2013, 02:12:57 amHameg does not offer combi scopes anymore, think this times are over. They only offer one last analog scope with a bandwidth of 40MHz but announced to cease production soon - no market anymore.I would also tend to buy a digital scope today but of better quality with sufficient bandwidth and wfm/s if communication electronics is an issue, but then it might become an expensive aquirement.From a few ham radio guys I know that they often search especially for analog scopes for their purposes, and bandwidth is more important than storage functionality. In this case sometimes you can get very professional scopes as the Tek 465 with various options for less money compared to an equivalent digiscope.There's no limit caused by the screen resolution with CRT as with TFT displays and the dead time is depending on the beam return, no processing time of data which causes limited wfm/s.But generally I agree, there have to be special applications for buying an analog scope today.Only my personal opinion, don't kill me for that, pleaseKind regardsGunb

author: Gunb
author_rank: Regular Contributor
timestamp: March 18, 2013, 09:58:03 am
content: Quote from: nctnico on March 13, 2013, 01:34:49 amOH YES!This is the scope that you had to fix with glue on your desk not to follow you like a dog when pulling the probe wire to hard!!! The screen was sooooo slow that you fall asleep when watching it too long.The reason why I decided to buy my good old Hameg HM407 combi scope in the 90s - fast CRT with digital option, much better than the TDS220 and it's ugly brothers and sisters.I think, that was also good reason for Agilent to produce digiscopes with CRT instead of using first generation of LCDs/TFTs as my 54622D.I've never understood why people liked this Tek series and spent much money for this Gameboy design !?!?

author: Unknown
author_rank: Unknown
timestamp: March 18, 2013, 12:20:15 pm
content: Don't knock on the TDS-220, it was a decent scope... in the mid-nineties. I believe it was (one of) the first affordable scope with a decent sampling rate (1 GS/s for 100 MHz BW). The competitive Agilent models of that time were stuck in the ~100 MS/s range, although with much more memory.The TDS-220 was intended to replace the analog scope for low-end service work. The fast sampling rate and peak detect mode made aliasing less likely, and analog scope users don't really need a long memory, 2.5k is plenty for a few screens full of data.Of course it's not very competitive to modern low-end scopes, just like a computer from that era is not very competitive to a modern computer. DSO technology was still in a fairly early stage back then, so naturally you see much more improvement going from a TDS-220 to a DSOX-2000 than from a Tek 2467 to an inferior modern analog scope (since the 2467 was essentially the end of the line for analog scope development).Quote from: Gunb on March 18, 2013, 09:43:43 amThe screen resolution of a reasonably modern analog scope is quite limited. To reduce the tube length, many later (from the seventies onward) feature an expansion mesh that blurs the trace. Nowhere the infinite resolution you might imagine. For very sharp traces showing tiny details, go for the older, mainly tube-based, analog scope. Nothing of this newfangled transistor stuff. The accuracy from a CRT is also quite limited, maybe 4-6 effective bits over bandwidth if you digitize them (they tried this in the early days of digital scopes).

author: EEVblog
author_rank: Unknown
timestamp: March 18, 2013, 12:41:48 pm
content: Quote from: alm on March 18, 2013, 12:20:15 pmYes, the TDS-200 series was the industry game changer. Overnight, affordable scopes went from crappy equivalent time sampling, to real time sampling on all timebase settings. And the industry never looked back, real time scopes became the norm. So hats off. But itwasalmost 20 years ago now!

author: GK
author_rank: Super Contributor
timestamp: March 18, 2013, 12:45:17 pm
content: I often find myself switching to an analog scope when the resolution of a DSO proves insufficient. A recent example was a low level burst of RF oscillation over part of the cycle of a repetitive low frequency signal. Completely invisible on the DSO (buried in the "digitization" noise) but clear as bell on the old Tek.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 18, 2013, 01:49:14 pm
content: The other thing is trying to look at 50Hz hum on a repetitive pulse train,or similar signal,which is a common problem in Electronic repair.The classic case I always quote,(ad nauseum),is looking at an analog video signal at field rate in order to find both hum & other artifacts at low frequencies.Most 1990s DSOs (& many inexpensive modern ones) are incapable of doing this,as they reduce their sample rate too far at long time/div settings,so that they run into problems with aliasing,due to the high frequency components of the signal.The last one we were shown at my old work would have worked well for NTSC,but still had problems with aliasing due to the PAL4.433MHz chroma frequency.As the last analog 'scope we bought had major problems,we ended up taking the flawed DSO as the best compromise replacement.Tek took the faulty analog back.

author: Gunb
author_rank: Regular Contributor
timestamp: March 18, 2013, 01:52:46 pm
content: Quote from: alm on March 18, 2013, 12:20:15 pmI wrote about former high end scopes like the Tek 465 that you could get for a small budget and of course I'm speaking NOT about scopes where the trace is blurred.And I can guarantee that even the trace of my HM407 standard scope is still very well, many other owners confirmed that, too.If I would buy an older scope at ebay I first would try to visit the owner to investigate the device.Quote from: alm on March 18, 2013, 12:20:15 pmYes, I mainly talk about pure analog tube-based scopes, the Agilent example related only on the faster screen - besides it also has got a tube. And of course the resolution of the CRT is higher, NEALRY limited by the width of the trace only. If we're talking about a 320x whatever pixel display you first have to zoom in if more samples are stored in the memory as displayed. The sample rate limits the physical resolution additionally, and related to this example more than 320 samples can't be displayed at once. Or how for example do you show 10kPts on a screen consisting of 320 pixels horizontally without zooming in??? Easier to see the glitch without zooming on an analog scope, there's no pixel limit. Checked a few times.If a glitch occurs between two screens you won't see it on a digital scope, but on an analog scope. On a digital scope you need high wfm/s to increase the probability to catch the glitch, on an analog scope set up with high time of persistence you can see it the first time it occurs.Quote from: alm on March 18, 2013, 12:20:15 pmBits over bandwidtch of an analog scope? Don't know where the bits should come from when talking about analog scopes like the Tek 465. Strange.Back to the TDS: didn't say anything about the sample rate or trigger capabilities but the bad slow display and it's cheap impression. Only my personal opinion

author: Gunb
author_rank: Regular Contributor
timestamp: March 18, 2013, 02:21:14 pm
content: FYI: Attached some useful information. Old but still informative related to the scopes we're talking about.Kind rgdsGunb

author: nicknails
author_rank: Regular Contributor
timestamp: March 18, 2013, 02:35:29 pm
content: Quote from: EEVblog on March 18, 2013, 02:12:57 amWhen I'm using an analog scope, for the most part I don't have to touch any trigger settings (unless I'm in single shot mode). Whatever my signal is shows up typically without any fiddling. I can bounce between different points on my board without even touching the scope.When I'm using the DSO, the trigger settings are incredibly sensitive. If my waveform changes a little bit, the signal on the screen goes nuts until I adjust the trigger level up or down a hair. It's just an annoyance. If I bounce between different points on my board, I have to stop to adjust the trigger levels and settings.Maybe it's just because I'm using low-end equipment. I have a Rigol DS1022C and a DS1102E.

author: c4757p
author_rank: Super Contributor
timestamp: March 18, 2013, 02:43:20 pm
content: I agree, but I think it is specific to the model/brand. My DS1102D is also insanely touchy, and my Tektronix 2445A triggers on anything without any adjustment at all, but the new Agilents in the school lab feel more like the Tek.

author: robrenz
author_rank: Super Contributor
timestamp: March 18, 2013, 03:10:41 pm
content: Quote from: GK on March 18, 2013, 12:45:17 pmYeah, like this:

author: Unknown
author_rank: Unknown
timestamp: March 18, 2013, 03:33:40 pm
content: Quote from: Gunb on March 18, 2013, 01:52:46 pmThe 465 features an expansion mesh. Customers complained about the blurry trace when it came out. Just compare it to the tube-based 500 series (and I believe some of the early 400 series) to see the difference.Quote from: Gunb on March 18, 2013, 01:52:46 pmThe 465 is all transistors, its only tube is the CRT.Quote from: Gunb on March 18, 2013, 01:52:46 pmThis depends on the edge rate. You can barely see the edges of a fast-rise square wave with a high duty cycle. Good luck catching that low duty cycle glitch. Finding them would require turning off the lights and cranking up the contrast. The exception to this is the MCP CRT that Tektronix only used in the 2467 and 7104. These where specially designed for these kinds of jobs, and had a kind of analog image amplifier. Consisting of tiny channels, kind of like pixels.Quote from: Gunb on March 18, 2013, 01:52:46 pmIt gives an indication of accuracy. You can calculate the accuracy from the ENOB if you feel like it, but ENOB is easy to compare to a digital scope. There was a project where they digitized the image of a CRT, but even after correcting for all of the distortion, the results where still quite horrible compared to a decent ADC. Shows that the CRT has resolution, but not accuracy.

author: Gunb
author_rank: Regular Contributor
timestamp: March 18, 2013, 04:23:40 pm
content: @alm:just have a look into my attached file above, that's what I'm talking about. And that's still valid concerning the TDS as well as current cheap digital scopes.Tek465 was only an example, I know a few people still using that device without any complains - don't have it, so I can only repeat what they are telling me.I've replied to the question if buying an analog scope still makes sense - and because of the facts in the attached document I would recommend to buy a used Hamegwith CRT or similar in good condition FOR SPECIAL purposes only. In general I would prefer a digital scope.Quote from: alm on March 18, 2013, 03:33:40 pmMaking an analog signal digital - with what? Who made it under which circumstances? Which scope was used for that purpose? Can it be generalised for every input amplifier of any scope manufacturer? Who can guarantee that the used ADC for conversion wasn't the part which made it horrible first?It's a fact, that an 8 bit ADC has got a resolution of 256 causing quantization noise. It's also a fact that any voltage level between two steps is assigned to the same quantized value. At this point the analog scope can show more resolution than the digital one, implied that the electronic of the scope is better than the required resolution.By the way I didn't talk about accuracy andverticalresolution, that's a new discussion you're starting now.I've discussed thehorizontalresolution and the fact that the CRT can display more details concerning the x-axis as described in the attached PDF above - seems to be a simple fact.

author: Unknown
author_rank: Unknown
timestamp: March 18, 2013, 10:55:49 pm
content: Quote from: Gunb on March 18, 2013, 04:23:40 pmThis is an attached ZIP file with presumably a PDF inside. It is served with the wrong content type, forcing me to download it, then unzip it, and read the PDF. As opposed to just clicking on the attached PDF. Probably not your fault but the fault of the forum/server administrator, but I don't feel like jumping through hoops right now.Quote from: Gunb on March 18, 2013, 04:23:40 pmThis was a Tektronix project. They attached a digital camera to a CRT to digitize it. Distortion was terrible. Real digital scopes (with a front-end that directly drives an ADC as opposed to a CRT) perform much better. No argument on the resolution, but don't let you fool that into thinking the accuracy is there. It's not.Quote from: Gunb on March 18, 2013, 04:23:40 pmThe vertical amplifier of an analog is definitely a weak link in the distortion performance. Just because the eye is a terrible judge of distortion does not mean the signal is undistorted, especially as the frequencies go up.Quote from: Gunb on March 18, 2013, 04:23:40 pmAssuming you can't use the zoom function on your DSO. Otherwise any modern DSO with 1Mpoints+ of sample memory will have much more horizontal resolution than an analog scope, but of course not conveniently in one screen.

author: nctnico
author_rank: Super Contributor
timestamp: March 18, 2013, 11:53:07 pm
content: Quote from: Gunb on March 18, 2013, 01:52:46 pmNot quite true. An analog scope also has dead-time because of the horizontal retrace and it needs to find something to trigger on unless its in free run but then you'll see just blurs. Some digital scopes (like the one I have) have a special mode in which it captures waveforms continuously without any dead time.In my experience a DSO can display a signal better than an analog scope but it takes more effort to set it up properly. Getting a blur to show on an analog scope is easy but that doesn't mean its a meaningful measurement.

author: Gunb
author_rank: Regular Contributor
timestamp: March 19, 2013, 12:24:23 am
content: Quote from: alm on March 18, 2013, 10:55:49 pmWho ever said I would?Quote from: alm on March 18, 2013, 10:55:49 pmNobody denied that, but it's possible to investigate how good the amplifier is, of any scope. But that's an issue of analog as well as digital scopes. There's still an analog input stage.Quote from: alm on March 18, 2013, 10:55:49 pmAha! I can't use the zoom?! Really? I mean, when using a scope with an ADC of 1GS/s at max I assume that you understand that the time between two samples is 1ns, right? So you're zoom can't resolve more than showing you samples in a distance of 1ns, what happens between is not displayed, but interpolated if not switched off. An analog scope using 1ns can show any value between because there's no sampling but a continous steering of the beam. Disadvantage: you can't store it. Think about it.

author: Gunb
author_rank: Regular Contributor
timestamp: March 19, 2013, 12:54:06 am
content: Quote from: nctnico on March 18, 2013, 11:53:07 pmOh man, I've already mentioned that issue a few times before, you should read all my comments before starting from the beginning.Quote from: nctnico on March 18, 2013, 11:53:07 pmYou see just blurs - aha - I can see a baseline in AUTO mode or nothing until a trigger level is reached in NORMAL mode. And your digital scope behaves different in AUTO or NORMAL mode? - strange! So you want to tell me that your digital scope DOES NOT need something to trigger? Funny! All my 4 digital scopes either run free or only if triggered.Quote from: nctnico on March 18, 2013, 11:53:07 pmAh, and what "magic" scope is that? I mean even the top scopes in the market have limited refresh rates, I'm curious what scope you're using!Quote from: nctnico on March 18, 2013, 11:53:07 pmSo, when I switch on my analog scope I don't see " a blur" - did you learn that term today? When I set my analog scope to 1mV/DIV and do the same with both digital scopes, the analog one has a nearly noise free beam deflected from left to right, my Rigol DS4012 produces so much noise caused by it's own ADC that 1mV/DIV is ajoke! The HMO is very fine, the noise level is nearly perfect and much better than most Agilents because of better ADCs.I've got a few scopes to compare - you also? And for me it's not a question of what I believe but what I see.Did you ever work with analog scopes and know what you're talking about? I can't really imagine.I recommend to read the doc I've attached above and try to understand it!

author: nctnico
author_rank: Super Contributor
timestamp: March 19, 2013, 01:40:36 am
content: I have a TDS744A scope with 'Instavu'. That should display up to 100k wfms/s. Ofcourse Rigol won't compare to an older real high end scope with a low noise input but that is no reason to say every DSO is crap. And yes I have used analog scopes. Actually my previous scopes could be used both analog and digital. But in the end I never really used the analog mode. In my experience the digital mode showed a much clearer image than the analog mode.About digitizing CRTs: that is done in some high speed oscilloscopes with a scan converter tube.

author: EEVblog
author_rank: Unknown
timestamp: March 19, 2013, 01:56:56 am
content: Quote from: robrenz on March 18, 2013, 03:10:41 pmI have a video uploaded and queued that shows how you can easily miss stuff on an analog scope that gets shown easily on a digital scope.(common mode noise is the example I used)Whether or not you want that stuff shown is another argument entirely, but it does show that analog scopes have disadvantages when it comes to this sort of stuff too.

author: BravoV
author_rank: Super Contributor
timestamp: March 19, 2013, 02:03:01 am
content: Its just a matter of time that analog scope will be gone one day, that is the undeniable fact.

author: Lukas
author_rank: Frequent Contributor
timestamp: March 19, 2013, 06:00:59 am
content: Quote from: Gunb on March 19, 2013, 12:24:23 amThat's only true for single shot signals. Even cheap Chinese are able to determine the timing relation between the sampling clock and the trigger to a resolution of 25ps, which gives you a timing resolution of 25ps when acquiring long enough.

author: Gunb
author_rank: Regular Contributor
timestamp: March 19, 2013, 08:42:54 am
content: Quote from: BravoV on March 19, 2013, 02:03:01 amOf course, and I wouldn't buy a new analog scope today. But that was not the issue, it's a fact that there are special purposes where a formerexpensive analog scopemightbe better than cheap digital scope of today. Or do you know a new 500MHz scope for a moderate price of less then 1000,- EUROsthat you can use for ham radio?That was my argumentation from the beginning without lowering the benefits of digital scopes, own myself a few.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 19, 2013, 08:49:56 am
content: Quote from: Gunb on March 19, 2013, 08:42:54 amIf you're on a limited budget, a cheap DSO plus a cheap old (originally expensive) analogue scope will give you the most functionality for your money.A DSO needs to have high update rate and an intensity-graded display to fully replace an analogue one - I think the Rigol 2000 is the cheapest new option unless you get a very good deal on a used Agilent 5/6/7000 or tek DPO

author: Gunb
author_rank: Regular Contributor
timestamp: March 19, 2013, 09:05:34 am
content: Quote from: Lukas on March 19, 2013, 06:00:59 amNo it's generally valid even for cheap Chinese scopes and it doesn't depend on single shot.- ADC with a sample rate of 1GS/s enables 1ns time interval between two samples - as given in my example- ADC with a sample rate of 4GS/s enables 25ps time interval between two samples - as you mentioned.But it doesn't influence the fact that a screen of limited pixels for example 800 pixels on the abscissa cannot display more than 800 pixels at once. Either the scope displays only each - lets assume - 10th sample of the sample memory on screen by transferring it to the display buffer or you have to zoom in until you see the samples in the distance of your 25ps, in this case your timebase is very small.That's how all digital scope work, cheap Chinese ones as well as expensive Agilents, Teks or whatever.In REFRESH mode digital scopes use double buffering, where one part of the memory is filled up with samples whilst the other part is displayed, which leads to the famous wfm/s limitation. Manufacturers as Agilent use special ASICs for generating high wfm/s with parallel processing where cheap scopes for hobby purposes use simple FPGAs which result in lower wfm/s.In SINGLE SHOT mode the scope fills up the complete memory with samples and stops. Depending on the chosen timebase the ADC might work with its highest sample rate, in my example I assumed an 1GS/s ADC, so the memory is filled with samples in a distance of 1ns - you can't fill it up with a higher sample rate than the physical limits of the ADC offers - even not with cheap Chinese scopes. And you can easely check that by switching off the interpolation & zoom in until you see the samples. Measure the time interval between two subsequent samples, just that simple. Done a few times.And we're not talking about random sampling, that's another construction and works for periodical signals only.

author: Gunb
author_rank: Regular Contributor
timestamp: March 19, 2013, 09:07:38 am
content: Quote from: mikeselectricstuff on March 19, 2013, 08:49:56 amExactly, I agree. Finally someone who understands what we're talking about.

author: nctnico
author_rank: Super Contributor
timestamp: March 19, 2013, 11:54:04 am
content: Quote from: Gunb on March 19, 2013, 09:05:34 amYou won't find a new analog or digital 500MHz scope for less than €1000,- so that argument is pretty moot. However there are lots of TDS500 and TDS700 series scopes on Ebay in that price range which have 4 channels and 500MHz bandwidth. If you are handy you can buy a cheaper defective one with the well known and documented problems and fix it.Quote from: Gunb on March 19, 2013, 09:05:34 amYou obviously never heard of peak detect which every decent DSO has. You really should learn how to use a DSO properly because you sound like someone trying to argue a vinyl record is better than a compact disk.

author: Gunb
author_rank: Regular Contributor
timestamp: March 19, 2013, 01:14:38 pm
content: Aha, so so. OK, after you let off the steam:1st : because you seem to be unable to read right, I spoke about ausedscope,not a new one2nd: I spoke about ananalogscope,not a digital one3rd: don't know why you explain to me what I've tried to explain to the opener of that thread, but it's pretty much your opinion4th: because you assumed - I did never claim that DSO are crap - you should read my comments more accurate5th: you're argumentation with your high price scope has again nothing to do with my initial statement: buy a used analog scope for less than 1000,- EUROs where your digital might not have enough ressources and be happy. Your Tek is even used beyound 1000,- €, so it's not discussable.6th:PEAK DETECT has nothing to do with the maximum sample rate of the ADC.WOW! What do you want to do with "Peak detect"? Increasing the physical limit of the maximum sample rate of an ADC???No?Then again your comment is off-topic, because that was my last comment about.Nearly any scope manual remarks to use peak detect when usingslow timebasesto revealsmall fast glitchessince thesample rate is also reduced.And? It's just a different option, but cannot overcome the maximum sample rate of an ADC.Don't know your problem, Mr. Recordplayer, but it seem's that you either have a problem to read things right or understand what they're about.You're really a funny guy. First you started with "there's not dead-time" although anybody using DSOs knows that wfm/s is exactly about it, thenyou compare cheap Chinese scopes with your nice still powerful high end device, that you still can't get for cheap, and now you try your luck withthe "peak detect" optionWhat comes next, the color of the probe?By the way: Agilent's manual for the 54622D explains for people like you very precise when peak detect can be helpful. Maybe your biggest mistake is that you relate to your powerful Tek than to these cheap Chinese models.Look at the attached diagram taken from Agilent. Even peak detect won't help you making the glitches visible, on an analog scope you might see it - and that's where the discussion started since the beam is usually much faster returned than the signal processing of a cheap & slow DSO. In this case an analog scope might be an advantage, in other cases not.And because it becomes more & more interesting to me to get your expert's opinion: the second jpeg I've attached shows a screenshot taken from my 54622D where I admit that it does not have a brand new ADC, but it's good for an example.The ADC has got a sample rate of 200MS/s at max, i.e. a resolution of 5ns/DIV. I switched off the interpolation between so you can see that samples appear in an exact time interval of 5ns according to the sample rate.Now tell me please how peak detect can reveal what's between two subsequent samples? I doesn't matter if switched on or off - there's simply no difference because working with the fastest timebase of the scope and the highest sample rate.There's no gap between two samples when using an analog scope, since the beam is continuously deflected. Must not, but might reveal more details in this case. Only compromise with a DSO: take one with a faster ADC to reduce the gap between the samples to a smaller time inteval.So, before telling me what I don't know, answer my questions, please.Kind regardsGunb

author: Unknown
author_rank: Unknown
timestamp: March 19, 2013, 05:23:36 pm
content: Quote from: Gunb on March 19, 2013, 12:24:23 amAnalog input stages for DSOs are generally better. They don't have to have the (relatively) huge voltage swing to drive the plates of a CRT, just the inputs of an ADC. This reduces much of the thermal problems they had with analog scopes.Quote from: Gunb on March 19, 2013, 12:24:23 amThis is a completely different argument, and is about bandwidth, not resolution. A digital scope with a sampling rate of 1GS/s will generally have a bandwidth of about 100 MHz. So the signal from the front-end will be pretty much identical between t and t+1ns. This is also what sampling theory tells us. Any signal you will generally use a 100 MHz scope for will be well below the Nyquist limit of 500 MHz.In an analog scope, the beam will be bandwidth limited by the vertical amplifier and CRT. So it will produce a smoothed version of the signal, with the higher frequencies attenuated. Kind of like interpolation.A signal with significant changes on time scales < 1 ns will have frequency content beyond 500 MHz. Are you really expecting your 100 MHz scope to give usable results at those frequencies?

author: Lukas
author_rank: Frequent Contributor
timestamp: March 19, 2013, 05:58:13 pm
content: Quote from: Gunb on March 19, 2013, 09:05:34 amThere isn't a big difference between random sampling and real time sampling + TDC for subsample trigger resolution. When switching to "dot mode" and enabling persistence a real time scope becomes equivalent to a random sampling scope, hence the time resolution is determined by the trigger TDC.Take a look at the DSOX2000 datasheet: horizontal resolution 2.5ps Pretty much every DSO has a time resolution better than it's sample rate, no matter if real time or sampling.

author: Gunb
author_rank: Regular Contributor
timestamp: March 19, 2013, 10:10:06 pm
content: Quote from: alm on March 19, 2013, 05:23:36 pmAh, OK, that might be the reason why a friend of mine at R&S told me that they've developed a low noise input stage linear over the complete 500MHz bandwidth taking a few years to design a special ASIC for their digital scopes - funny, it could be so simple. Maybe they should have asked you?!Quote from: alm on March 19, 2013, 05:23:36 pmWow! Now even you've understood what I'm talking about all the time! Great, now you should understand that there's also a horizontal resolution caused by the sample rate of an ADC! Fine!Oppenheim/Schafer might help.Quote from: alm on March 19, 2013, 05:23:36 pmOh, now we start with Nyquist, why not! I assume you mean 50MHz, not 500MHz in your example above. And yes, when you relate to a simple sine, 50MHz is maximum, but if you want to distinguish a sine from a ramp, then even about 20MHz is allowed for the signal.But independent from Nyquist you're allowed to oversample a signal with more then twice of the highest frequency, right? And what else could be the advantage even if you're scope is limited to 100MHz bandwidth? Right Sir, the gap between two samples becomes smaller, so probality to catch a small pulse between subsequent samples is growing!And that's exactly the reason why a scope as for instance the Rigol DS4012 with 100 MHz bandwidth and a 4GS/s ADC reveals more details then a scope with only 1GS/s and the same bandwith.Nyquist is not the only criteria.Quote from: alm on March 19, 2013, 05:23:36 pmOh no, how many times do I have to emphasize thatI'm not talking about the VERTICAL resolution? Is it really so difficult to understand?Quote from: alm on March 19, 2013, 05:23:36 pmHä?Just for you: take an 80MHz signal, sample it with 1GS/s and again with 4GS/s, both scopes have got 100MHz bandwidth. Then follow my steps above: switch off the interpolation and take a screenshot as I did above with the Agilent.I tell you, what you'll get:- one screenshot where samples will have a distance of 1ns with the 1GS/s ADC- one screenshot where samples will have a distance of 0.25ns with the 4GS/s ADCAnd now you're allowed to guess where the probality to see a small glitch of 0.5ns is higher? Correct, the scope with the 4GS/s ADC!!! Well done, boy!And that has nothing to do with the bandwidth or Nyquist!Just interfere a sine with small glitches and use both scopes to see the difference. Difference between theory and practice - my eyes are not too bad to see the difference.

author: nctnico
author_rank: Super Contributor
timestamp: March 19, 2013, 10:39:21 pm
content: You really have no clue about digital signal processing and what bandwidth actually means...

author: Gunb
author_rank: Regular Contributor
timestamp: March 19, 2013, 11:33:04 pm
content: Quote from: nctnico on March 19, 2013, 10:39:21 pmWe've got you to be teached by clever answers like this without proving the opposite, guy.Be glad not to know what I'm doing every day and where I workMaybe you've got oneof the products I'm designing on your deskBut: there are lots of well made Agilent app. notes that you can use for the beginningwhere many things you don't understand are described very well.RgdsGunb

author: Gunb
author_rank: Regular Contributor
timestamp: March 19, 2013, 11:42:11 pm
content: Quote from: Lukas on March 19, 2013, 05:58:13 pmAnd also: wrong again.If you would understand the datasheet right, you could have noticed that the 2.5ps have nothing to do with the sample rate provided by the ADC.If you would have read the manual of the DSO2000X series well, you could have noticed that Agilent specifies a sample taken each 500ps provided by the 2GS/s ADC, German manual, page 158, above. Sounds logical to meAnd there's a tremendous difference between ETS and real time sampling. First implies a repetitive signal to take samples from several periods with a small delay from period to period. Putting them all together results in a higher horizontal resolution. Can't be done with non-periodic signals.

author: PA4TIM
author_rank: Super Contributor
timestamp: March 19, 2013, 11:50:43 pm
content: Befor you digital guys kill each other, there is a reason I still use my real scopes ( my DSO is a Hameg 350 MHz and it it great, i had a 100 MHz Rigol and that was crap)This reasons for using my 547 and 7603/7704 are- they will probably outlive me- are easy to repair- heat my lab- the plugin system is great, i have a transtistor Tr plugin, slide-back plugin, uV plugins, differential plugins, TDR, 1 GHz, opamp plugin ect.- supersharp trace ( 547) with fery low noise- what you see is there, not the games a DSO can play- very sturdy and foolproof, things like 500V max input using a 1X probe instead of the pitty 50V of many DSOs.- for RF, like modulation they are great- when repairing high voltage stuff like tube amps I use analoge scopes- they (547) are pieces of pure analoge art- there are dual beams ( to bad I do not have a 556 yet)- easy to operate, knobs for everything- weight, you do not pull the scope from the bench that easy- XY mode, multitrace like curvetracingDisadvantages- big to huge- powerhungry- no on screen info, i like the measure data on my dso, beats counting devisions and doing the math.- the movement of the horizontal base is more easy then using the trigger, holdoff, delayed timebase ect.I use my Hameg about 80 % of the time, for the rest the 547 or 7603.Last week I repaired a satelite tuner, there was so much crap on the psu signal ( high switching peaks, digital garbage, ripple, the Hameg had troubles catching it. It was capable but needed a ot of fiddeling with the settings. Then I took the 547 and in 30 minutes all bad caps were found and replaced. I had that in the past with the Rigol, i made a CW decoder but it would not work right ( the analog part) the Rigol showed perfect pulses. Then I took the 7603 and then I did see the problem at once. Some pulses were lower in amplitude or chopped. The Hameg is a lot better at that point.The thing that made me trust dso's less however was a Trr diode measurement. The Rigiol shreenshot I had saved, later I used the same setup with the hameg and a 1 GHz analg sample plugin and the 7603. The Rigol was so far off it was almost scary.Both are 1n4148 reverse recovery time shots using the same setupBut I think a good DSO outperforms a good analog scope on most points and is general perfect usable. But then you talk out of the hobby budget. I rather have my 50 MHz acurate 547 as a 100 MHz lying Chinese toy scope. ( and i have the gear to check, most pro-toy teardowns are not against references, hell, some not even have a signal generator of function generator and still tell the toy performs well. Yeah, whit the standard crappy not enough BW probes but nice colors, a great giftbox and it powers up.

author: nctnico
author_rank: Super Contributor
timestamp: March 20, 2013, 12:22:56 am
content: No wonder the Rigol is so far off. It doesn't have 50 Ohm inputs (which you use on the Hameg) and its bandwidth is probably too limited for what you want to measure. You just choose the wrong tool for the job. If you measure a 50MHz square wave with a 100MHz scope you'll get something that looks line a sine wave but you can't tell what the signal really looks like. Its like trying to measure millimeters with a ruler which only shows centimeters. There is always a limit to the usefulness of a tool but that doesn't make it a bad tool.

author: PA4TIM
author_rank: Super Contributor
timestamp: March 20, 2013, 12:44:01 am
content: Dream on, ever heard of inline termintors ? I have done the same measurement also using a 100 MHz 7603 and that was more like the Hameg, a bit slower but as clean.The bandwidth has nothing to do with it. I have done a lot of BW testing so I know the differences, what you tell about squarewaves that look lile sines ? Look at my website, the pictures are there showing wath you tell. This has to do with things like for instance the phase offset between channels, the huge difference in Trr, much more as BW should give and difference in the trace going all over the screen. I have the same hoorible differences while doing load tests, had to use filtering ect to get a usable trace that still looked like shit from the noise, the Hameg draws it as sharp as a rothring pen. The analoge scopes too.I May not be an expert on how the digital stuff calculates and translates the signals but I think I can say I do know scopes and for most how to correct use them.Measured even things like input impedance over a few hundered MHz with a vna, measure that on a Rigol and you do not need a 50 Ohm input, unless you want to increase the imput impedance >:-), i have scoes to 5 GHz, tested probes to the limit ( that way I found out the Rigol 100 MHz probes are indeed 100 MHz, the scope is too, so do your math....A 100 MHz tek probe is more then 100 MHz, it is made for a 100 MHz scope and made to be sure a 100 MHz scope can use that 100 MHz.

author: Gunb
author_rank: Regular Contributor
timestamp: March 20, 2013, 01:05:50 am
content: Yes,and that's what I've also noticed: the RIGOL DS4012 isn't a cheap scope and it has got 1mV/DIV sensitivity, also my HMO2524 and the analog HM407. Both Hamegs have got extreme low noise levels, but the Rigol seems to be connected to a noise generator. It has got 1mV noise floor, so the 1mV/DIV can't be used for small signals. It's a good scope, but not usable for that purpose. So I prefer the HM407 in analog mode or even the HMO with its reference class ADC rather than the RIGOL.The trace width of both Hamegs does not even become bigger when changing to 1mV/DIV, can't see noise at all.That's why my initial recommendation was to extend a cheap DSO with an older analog scope of good quality if people have a limited budget only.

author: madshaman
author_rank: Frequent Contributor
timestamp: March 20, 2013, 02:04:20 am
content: I may not know much but I know this, if someone made a new 10Ghz crt-based analog-only scope I could afford, I'd cry tears, then I'd happily pull out my wallet.In fact, I'm pretty sure that's what I want to try and build. Know idea how long the learning process and the attempts at construction of each part would take me, but that seems like a happy road. (And yeah, extending it by adding a high speed ADC, writing software, is logical next step)That aside, I use my analog scope (400Mhz) more than my digital one (200Mhz, 8-bit, 1GSa/s single shot), that might change over time. Right now it's mostly a subjective choice, I like using it more. Only one single problem: can't really scope circuit startup/shutdown or other kinds kinds of single shot events with an analog scope.

author: Lukas
author_rank: Frequent Contributor
timestamp: March 20, 2013, 05:59:02 am
content: Quote from: Gunb on March 19, 2013, 11:42:11 pmWhere did I say that?Quote from: Gunb on March 19, 2013, 11:42:11 pm500ps sample resolution vs 2.5ps time resolutionQuote from: Gunb on March 19, 2013, 11:42:11 pmOf course, my statement was based on repetitive signals. In single-shot applications the time resoultion is equivalent to the distance between the samples. When acquiring repetitive signals a real time scope behaves identically to a random sampling scope (with a high sample rate)To clarify my point: Time resolution of DSOs acquiring repetitive signals is determined by the trigger TDC, not by the sampling rate.

author: nctnico
author_rank: Super Contributor
timestamp: March 20, 2013, 07:24:46 am
content: Quote from: PA4TIM on March 20, 2013, 12:44:01 amA Trr measurement basically sends a step into the oscilloscope which is nasty. Depending on the frequency response you can get the effects shown on the Rigol. Agilent has an appnote on this:http://cp.literature.agilent.com/litweb/pdf/5988-8008EN.pdfIn short: it comes down to how the input filter is implemented. A sharp filter will cause ringing but prevents aliasing due to the sampling frequency.In most practical cases a scope (analog or digital) shows an interpretation of a signal anyway. A 1kHz 1Vpp sine wave will show fine on any scope but at higher frequencies and/or low amplitudes all bets are off. If you measure a signal with a scope you have to factor in its limits. IOW you have to know what the signal looks like and how your scope shows such a signal given its limits. In some cases a signal will show just garbage which means you need to get a better scope.

author: Gunb
author_rank: Regular Contributor
timestamp: March 20, 2013, 08:12:22 am
content: Quote from: Lukas on March 20, 2013, 05:59:02 amWhy do you mention it then - makes no sense to discuss off-topic?!Quote from: Lukas on March 20, 2013, 05:59:02 amAnd? Tell me how you get more samples than the ADC can provide at max - that's the issue I'm talking about - has nothing to do with your 2.5ps, absolutely nothing.Quote from: Lukas on March 20, 2013, 05:59:02 amAnd? Has nothing do to with the issue of that thread, and has nothing to do with my previous comments. Can't use ETS for most of my purposes since the signals I'm processing are seldom periodic. Again: that has nothing do to with my previous statements.

author: Unknown
author_rank: Unknown
timestamp: March 20, 2013, 08:40:16 am
content: Quote from: madshaman on March 20, 2013, 02:04:20 amNot going to happen. Try making a CRT with that kind of bandwidth. They were approaching the limits of what CRTs could do at the end of the analog scope era. The highest end analog scopes went up to a few hundred MHz, with a select few scopes going up to 1GHz. You can go higher, but then limited deflection becomes a problem. I believe a Soviet company designed a digitizer (basically a CRT with a video camera in front) with a few GHz bandwidth. The CRT was too long to fit into a standard 19" rack, something like 1m long. This would be extremely expensive, and also kind of bulky. I don't think much progress has been made in CRT technology since then, since the only analog scopes that have been designed since are low-end scopes.

author: Unknown
author_rank: Unknown
timestamp: March 20, 2013, 08:53:13 am
content: Quote from: Gunb on March 19, 2013, 10:10:06 pmThe Nyquist limit states the maximum bandwidth of the signal (it assumes bandwidth limited signals) that you can completely (!) reconstruct at a given sampling rate. This is half the sampling rate, so 500 MHz for 1GS/s.Quote from: Gunb on March 19, 2013, 10:10:06 pmIf the front-end limits the signal to 100 MHz, there is no pulse going to be smaller than 1 ns. You can't construct a 1 ns pulse from sine waves (Fourier series) with frequencies up to 100 MHz. Of course the front-end won't have a brick-wall response, which makes the issue slightly more complex.Quote from: Gunb on March 19, 2013, 10:10:06 pmHorizontal resolution is linked to bandwidth. What good is horizontal resolution of the high frequency components of your signal (necessary to actually see changes at those time scales) are attenuated?Quote from: Gunb on March 19, 2013, 10:10:06 pmWhy would you switch off interpolation? Interpolation is an essential part of sampling theorem. It says you can reconstruct (with interpolation) a signal.Quote from: Gunb on March 19, 2013, 10:10:06 pmIf there is a small glitch of 0.5 ns, it is not an 80 MHz signal, and the glitch most likely won't make it through the front-end unless it had a very large amplitude.

author: PA4TIM
author_rank: Super Contributor
timestamp: March 20, 2013, 08:59:31 am
content: Quote from: nctnico on March 20, 2013, 07:24:46 amRead the appnotes from Williams about scope mesurements. He often shows how to get it right and how to reognize faults in screenshots/setups.A step is not nasty, it is a way to seperate the boys from the men. But I know what causes the things the Rigol shows and that is not why I showed that pictures, the point is, my other scopes did not make such a mess out of it. Gunb tell it right, the Rigol has a build in noise generatorQuoteI agree, and the Rigol showed a very bad interpretation. Because I know what to expect while measuing, most signals showed as garbage and I measure a lot against the limmits, I knew I needed a better DSO and that became the Hameg.Do not forget we often compare horses and cows when it comes to scopes. Our beloved analoge sopes were often state of the art at that time and build with no cost spared. Specs were worst case numbers and you could trust then.They still make quality like this, but only a few members here have acces to DSO's that have that level. They costed a fortune back then, they cost a fortune now. I'm talking integrety off measurements, optimalision of input and other stages, quality of used components, ect. But because BW has gone skyhigh on the still very topmodels now, we wrongly compare the low BW budget models from today with the topmodels from back then, the only thing they have in common is that BW. The rest is at a totally different level. The toys do not even have real specs, they are just "avarage" or " typical" or "best" and often pure theoretical or just picked by marketing.Madshaman:Forget building a 10 GHz (analog crt) scope. There has been a 1GHz realtime Tek, the CRTs for those are extreme and very rare. You will not find a CRT that does 10 GHz without sampling. An analog sample scope only needs a 10 to 20 MHz baseunit.Try building a 10 MHz scope first, including triggering, several timebases and calibrated V/div input section. Then the right delay network, low noise amplifiers flat over 10 MHz and the high voltage part, 100 MHz scopes go over 10kV for the CRT, and defelection voltages go up too because they are related. Vertical and horizontal amplifiers from analog scopes are state of the art designs and even today used as examples in modern analog design literature. ( i have two books where the writers use Tektronix amplifiers from the 60/70's for this)

author: Gunb
author_rank: Regular Contributor
timestamp: March 20, 2013, 09:11:06 am
content: Quote from: nctnico on March 19, 2013, 10:39:21 pmSo, too tired of your bullish behaviour yesterday I take a last try to examine what I've already implied when joining the discussion at the beginning and where youstill got stuck:Requierements:- Scope with 100 MHz bandwidth- Square wave of 7MHz , 50% duty cycleLet's assume we want at least 5 harmonics:f0 = 7MHz (1. harmonic)f1 = 3*7MHz = 21MHz (2. harmonic)f2 = 5*7MHz = 35MHz (3. harmonic)f3 = 7*7MHz = 49MHz (4. harmonic)f4 = 9*7MHz = 63MHz (5. harmonic)- Since we've got 50% duty cycle we only will get odd multiples of the base frequency.- Since we're 37MHz away from the 100MHz cut-off frequency we are on the safe side getting all 5 harmonics with no/less than 3dB attenuation.Concludingly, our 100MHz scope is still sufficient concerning these facts. Are we still friends at this point?Now we go on with the ADC and the required sample rate. Nyquist says, at least sample rate has to be 2x of the highest frequency the signal consists of.So, with f4=63MHz we should have at least:- fsample = 2*f4 = 126MHz = 126MS/sThe old Agilent I'm using has got 200MS/s, so sufficient for the example above and exactly twice of the scope's bandwidth.Means also, a 100MHzsinewill be attenuated with 3db at the scope's cut-off frequency and if sampled not at the zero crossings you will even see something on screen.Of course, that's not sufficient for asquare wavewhere the harmonics are of higher frequency than 100MHz. In this case - as you also mentioned - you'll only see somethingthat looks like a sine, since harmonics are missing.Think, we're still friends at this point, right?BREAK: all these thing I've implied when joining the discussion, these are basics that everybody should know using a DSOBut that's where you've started and what I've alreay passed.With all that basics in mind, now the pointwhere I've started this thread:- 3 scopes: all with 100 MHz bandwidth,- supposed that the maximum signal frequency we want to use them for is 100MHz (cut-off, 3db attn.)scope 1 with ADC: 200MS/sscope 2 with ADC: 1GS/sscope 3 with ADC: 4GS/sThe 200MS/s ADC is absolutely sufficient concerning Nyquist for a scope with 100MHz bandwidth.So the question comes up:what advantage can there be to use a 1GS/s or even a 4GS/s ADC for a 100MHz bandwith limited scope?-> They're completely oversized according the requirements of Nyquist.-> but, if we don't think of Nyquist at this point and search for further advantages we notice that the gaps between two subsequent samples isonly determined by the ADC's sample rate, so:- the 200MS/s ADC will generate samples with a time interval of 5ns- the 1GS/s ADC will generate samples with a time interval of 1ns- and last but not least the 4GS/s ADC will generate samples with a time interval of 250ps3x sampled the same signal:- interpolation leads to smoother signals concerning higher sample rates- more details are aquired because of smaller gaps the higher the sample rate, independet of Nyquist.These facts you can try yourself with any DSO, are mentioned in nearly any app. note from Agilent, Tek, Hameg, ... whateverand are even part of the books about the basics of how to measure right with DSOs.Don't know, why it's so difficult to understand.Believe me, my friend, I'm busied with signal processing more than 20 years now, especially the hard cases where disturbed signalshave to be processed, but the issue we're talking about in this thread are of quite common nature, nothing special.Sometimes it might be useful trying to understand what other participants want to explain before keeping them for stupid.However, have a nice day,Gunb

author: Gunb
author_rank: Regular Contributor
timestamp: March 20, 2013, 09:26:42 am
content: Quote from: alm on March 20, 2013, 08:53:13 amBut you might see parts of it, and that has got an influence on the signal you sample.Why switching off interpolation? Only for making the argumentation clearer and to see that the gap between subsequent samples is smaller with higher sample ratesthan with ADCs of lower ones. You simply get closer to the original analog signal then.Some people seem not to know that. Interpolation is always approximation of the real analog signal, when you want to see the samplesitself for researching the samples in memory it can be useful to switch it off. Needed that a few times for DSP processing of weak disturbed signals for synchronisationof a digital matched filter algorithm. In this case interpolation is not useful because I'm calculating with the real samples in memory that I've to see and not the "falsified"connection between samples added by the scope for improving visualization.Kind regardsGunb

author: Unknown
author_rank: Unknown
timestamp: March 20, 2013, 09:36:05 am
content: Quote from: Gunb on March 20, 2013, 09:11:06 amAn important point is that the definition of bandwidth in sampling theorem (the highest frequency component in the signal) does not match the definition used in filters and test equipment (-3 dB point). 200 MS/s is sufficient to sample a bandwidth-limited signal with no frequencies beyond 100 MHz. If there are frequencies beyond 100 MHz, it will screw up the interpolation. This is why usually figures like 4-10x bandwidth are quoted for the minimum sampling rate of a scope with a Gaussian (-6dB/octave) response. Only about 2.5x is necessary for scopes with a sharper roll-off, the so called brick-wall response (which is not really like a brick wall, but much sharper), since less higher frequency components will make it past the front-end. Another factor is that interpolation algorithms are not perfect, so having some head room beyond the Nyquist frequency makes interpolation easier. The 100 MHz/1GS/s example comfortably meets these limits.Quote from: Gunb on March 20, 2013, 09:11:06 amNone if the scope is really bandwidth-limited in the Nyquist sense, and you use perfect sin(x)/x interpolation. In the real-world case the 1 GS/s scope will perform better for some signals, but 4 GS/s is unlikely to make much of a difference unless you have specific signals with a large amount of frequency content beyond a few hundred MHz that will make it past the front-end somehow.Quote from: Gunb on March 20, 2013, 09:11:06 amThere are no more details to acquire in a bandwidth-limited signal. And it's hard to see how components even approaching the 500 MHz nyquist frequency of a 1GS/s scope will make it past the 100 MHz front-end. Responses tend to fall off much sharper than 6 dB/octave if you go well beyond the rated bandwidth, in my experience.Quote from: Gunb on March 20, 2013, 09:26:42 amThe low frequency parts will not need > 1 GS/s to reconstruct.Quote from: Gunb on March 20, 2013, 09:26:42 amInterpolation also gets you closer to the analog signal. That's what the whole Nyquist-Shannon-Whosthatthirdguy (Whittaker?) sampling theorem is about.

author: Gunb
author_rank: Regular Contributor
timestamp: March 20, 2013, 09:40:26 am
content: @alm:I find it always funny that most of your statements exactly say the same I've mentioned beforeSo, what do you try to explain to me, then? Cut-off frequency and limited devation of filter curves?Think, it's not necessary to waste time with the basics.I agree that I don't go into the details as you do, that would blast that thread completely with moreand more discussions.I also agree in all of your above explanations, but especially that statement:Quoteis one of the major issues which fits my case and where the higher sample rateeven of the 100MHz version was helpful a few times.The application: few kilometers of long harness wire in the open field with signal replies of a about 100mV and disturbed by externalnoise and glitches much stronger then the signal itself.

author: tinhead
author_rank: Super Contributor
timestamp: March 21, 2013, 04:13:34 pm
content: Quote from: Gunb on March 20, 2013, 09:11:06 amyour statement is a little bit misleading, something like "5. harmonic" could be read as5th harmonic,but here it is 9th harmonic you taking about. It is easier, even in the 50% duty case, to call them what they are,multiplied fundamental frequency.

author: PA4TIM
author_rank: Super Contributor
timestamp: March 21, 2013, 04:35:10 pm
content: The fundamental frequency fo, is called the first harmonic, so here f1, is the second Harmonic, so f4 is the 5th harmonic like Gunb wrote.But I'm not sure about the f1 ect notation, most times I read fo as fundamental, sometimes f0 ( f zero). As far as I know it is fo, if it is fo then f1 ect seems not to be right.What is the correct notation ?

author: madshaman
author_rank: Frequent Contributor
timestamp: March 21, 2013, 05:05:00 pm
content: Quote from: PA4TIM on March 20, 2013, 08:59:31 amYeah, soon as the idea occurred I realised that the CRT would be the limiting factor, so 1Ghz CRT is as high as was ever produced? Which books do you have or could recommend for ground up oscilloscope design? I think I would like to try and build one, do you think there's merit in learning/building an analog scope first then move to ADC later? Starting with a lower bandwidth and getting everything right does sound like the best approach to start.

author: Gunb
author_rank: Regular Contributor
timestamp: March 21, 2013, 05:14:39 pm
content: Quote from: tinhead on March 21, 2013, 04:13:34 pmAgreed. You're right.

author: tinhead
author_rank: Super Contributor
timestamp: March 21, 2013, 05:43:35 pm
content: Quote from: PA4TIM on March 21, 2013, 04:35:10 pmlet's get through the org. posting:f0 = 7MHz (1. harmonic) <- not exactly,f0 is fundamental, f1 is 1 harmonic - yes, they same, i know it.f1 = 3*7MHz = 21MHz (2. harmonic) <- wrong, f1 is 1st harmonic, 3 time the fundamental is 3rd harmonic and not 2.harmonicf2 = 5*7MHz = 35MHz (3. harmonic) <- wrong, f2 is 2nd harmonic, 5 time the fundamental is 5th harmonic and not 3.harmonicf3 = 7*7MHz = 49MHz (4. harmonic) <- wrong, f3 is 3rd harmonic, 7 time the fundamental is 7th harmonic and not 4.harmonicf4 = 9*7MHz = 63MHz (5. harmonic) <- wrong, f4 is 4th harmonic, 8 time the fundamental is 9th harmonic and not 5.harmonicbut i think it should be as following:f0 = 7MHz or f1= 7MHz (1. harmonic or fundamental)f3 = 3*7MHz = 21MHz (3. harmonic)f5 = 5*7MHz = 35MHz (5. harmonic)f7 = 7*7MHz = 49MHz (7. harmonic)f9 = 9*7MHz = 63MHz (9. harmonic)We have now 5 components of the waveform but not "5. harmonics".I don't like wiki as reference, but yeah:http://en.wikipedia.org/wiki/Fundamental_frequencyand here something about harmonics:http://www.allaboutcircuits.com/vol_2/chpt_7/2.htmland a nice video as well (for those who like "visual" things)

author: nctnico
author_rank: Super Contributor
timestamp: March 21, 2013, 06:08:15 pm
content: The whole purpose of an oscilloscope is that it should produce a pretty picture humans can recognise as a waveform.If you sample at twice the bandwidth you have all the information in the signal up to the specified bandwidth (the sharpness of the filter determines the actual bandwidth). The downside is that you'll need math intesive algorithms like polynomal approximation to show a signal instead of some seemingly random dots. Another problem is that a very sharp filter causes ringing in the passband so the frequency response isn't flat. Again this could be compensated in software at the expense of processing power. An easy way out is to sample a signal at a samplerate >=5 times the bandwidth (where the samplerate can also be achieved by using time equivalent sampling). This way interpolation is easy and the input filter doesn't need to be sharp which makes it easier to build and gives a flatter (Gaussian) frequency response.

author: tinhead
author_rank: Super Contributor
timestamp: March 21, 2013, 06:27:12 pm
content: Quote from: nctnico on March 21, 2013, 06:08:15 pmGaussian frequency response is never flatTo get flat response you need Butterworth- / Chebyshev-like filter, not Gaussian.

author: Unknown
author_rank: Unknown
timestamp: March 21, 2013, 09:10:34 pm
content: Quote from: madshaman on March 21, 2013, 05:05:00 pmYes, I'm pretty sure 1 GHz was the highest, at least in a western commercial design. There may have been some wacky Soviet design with a CRT that was a few meters long that went higher. There have been some transient digitizers (which use scan converter tubes) that went higher, but these are not scopes in a traditional sense (although they used a CRT).The most in-depth books on scope designs are probably the Tektronix Circuit Concepts book. These were from the sixties, but went into a lot of detail. Later publications are much more superficial. Just compare the current 'ABCs of probes' appnote with 'oscilloscope probe circuits'. Many of them are availablehere. There also used to be a seller on eBay selling a CD with all of them. Some of the circuits still apply, not all of course. I'm guessing the trigger circuits they show involve tunnel diodes, for example. Many ideas will still be relevant, especially for an analog scope.An analog scope will involve some extra complexity (the CRT itself, high voltage supply, driving the plates). Not sure how this is any easier than hooking it up to an ADC. Could still be educative, however. I would probably get a CRT from an old scope, preferably one with documentation. Manufacturing these yourself will be a huge project, and using a TV/computer CRT will seriously limit the bandwidth.

author: PA4TIM
author_rank: Super Contributor
timestamp: March 21, 2013, 10:18:34 pm
content: The tektronix circuit concepts books are great. I have a hole sersies of them, they were still unread when I bought them. Too bad I have the TDR version only as pdf.Seibt, handbook of oscilloscope technology is also a nice reading and Tek had a book that was called troubleshooting your scope ( or something like that, also very educationl)Both are downloadable from Kurts Tek Wiki.Some time agoo I got a rare gemanium transistor missing for my 1S1 1GHz sample plugin. I placed it today instead of the silicium I used and could not wait to try. The 1S1 performed less as my Philips 1 GHz sample scope but with this transistor it now is great. Nice sharp traces, before this I had to fiddle the trigger knob to find the sweetspot, now I had a trace at once and could use the trigger to stabalize it. So i'm very happy. ( and now time to repair my second 1S1)Used a very fast Tek pulser ( > 100 MHz) to test it, nice clean Pulses. Then I connected it to my DSO ( 350 MHz Hameg) to play with max sample rates, max wfu/s, peakdetect ect.Very educational, i managed to get "fantasy" traces. One moment my pulse had several spikes growing from the edges of the pulse. ( 105 MHz pulse at something like 25 Gsa/s equivalent sample time ). Very funny but I was amazed upto what speed the Hameg still gave a rather recognisable shape of the pulse. Even at 100MHz you could still see it was a squarewave and not a sinewave.

author: robrenz
author_rank: Super Contributor
timestamp: March 22, 2013, 12:39:13 pm
content: Quote from: EEVblog on March 19, 2013, 01:56:56 amI watched the video, It was excellent but I didn't see what would be missed on an analog scope? This would be an great time to do a contrasting follow up video about why a high gain differential probe/amplifier would be nice to measure the output ripple.

author: madshaman
author_rank: Frequent Contributor
timestamp: March 22, 2013, 08:20:59 pm
content: Quote from: alm on March 21, 2013, 09:10:34 pmThis kind of technology interests me too :-)QuoteOh thanks! That's an awesome link, reading through these will be better than sex; I mean that quite literally.QuoteWell, I do have a vacuum system and know a glass blower... but no, seriously, not quite ready to add CRT construction to the table, got enough on my plate at the moment.It's settled, I'm going to go for it, starting with buying a couple used oscilloscope CRTs, hopefully the same make (I usually get at least two of a new thing I'm going to try working with, chances are good I'll kill one before I know what I'm doing).The goal will be a 10Mhz scope, that should probably keep me busy.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 23, 2013, 03:39:19 am
content: Quote from: robrenz on March 22, 2013, 12:39:13 pmI'm sorry,Dave,but I didn't really see anything in that video where a digital 'scope was necessary,either.The interfering signal was repetitive,& an analog instrument would have no problem seeing it.Even if it just appeared as a thickening of the trace,the first thing I would do would be have a look at 5ms/div to see if it is 50Hz or 100Hz hum,then look at higher frequencies.----maybe a bit slower,but still easy ehough.Actually,once you know it isn't hum,you don't really need to accurately identify its frequency,just find the source.Or are we not talking about the same video?Sorry again,Dave,I just saw your new video,haven't watched it yet

author: nctnico
author_rank: Super Contributor
timestamp: March 23, 2013, 12:15:32 pm
content: Quote from: tinhead on March 21, 2013, 05:43:35 pmYou are right. Harmonics are numbered as multiples of the fundamental frequency. In the video you can clearly see that a real square wave has even harmonics as well (due to the finite rise/fall time).

author: jahonen
author_rank: Super Contributor
timestamp: March 23, 2013, 01:28:12 pm
content: Quote from: nctnico on March 23, 2013, 12:15:32 pmActually, even harmonics are produced by some sort of asymmetry of the waveform (for example, duty cycle not exactly 50%), not due to finite rise/fall. Or, of course if rise/fall times are different, that is also asymmetry which qualifies. Finite rise/fall times cause the envelope of the harmonics to fall faster (40 dB/dec) after some frequency determined by the rise/fall time.Regards,Janne

author: edavid
author_rank: Super Contributor
timestamp: May 30, 2013, 05:57:52 pm
content: Quote from: madshaman on March 21, 2013, 05:05:00 pmThe CRTs in the Tek 7904A and Tek 7104 were good to at least 2GHz, but were limited by the electronics. I'm sure a new design could be faster.There is a French company called Greenfield Technology which sells a 7GHz CRT-based transient digitizer. That CRT is easier to build than a direct-view tube, since the vertical deflection is smaller, and it uses a silicon target instead of phosphor.http://www.greenfieldtechnology.com/-Data-aquisition-system-.html