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Tektronix 1-3 GHz touch screen color DSO back in 1989 !
David Hess:
--- Quote from: Wuerstchenhund on August 21, 2017, 03:34:02 pm ---A digital scope is either a real-time scope (aquires the waveform in real-time) or a sampling scope (i.e. it acquires the waveform over multiple acquisition passes).
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Great! So depending on the time/div setting and the input frequency content or bandwidth limiting, a DSO could be either. Or maybe all of those DSOs which can operate either way are a myth. That sure unambiguously simplifies things.
--- Quote ---Both the 2230 and the 7854 are are analog/digital combi-scopes which both reach their analog BW in repetitive sampling or analog mode only. You're right that none of them are true sampling scopes as they are combi scopes with an analog and a digital mode.
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The analog capability of these oscilloscope is irrelevant to the discussion. Why bring it up?
And you are flat out wrong. Neither of these oscilloscope are bandwidth limited below Nyquist. The bandwidth for both is independent of sample rate. This is easy to demonstrate by making an RMS noise measurement at different sample rates; lower sample rates which cause aliasing do not change the measured amplitude because the input bandwidth does not change. The same measurement made of a sine wave or any other signal will produce the same result. Some DSOs take advantage of this for their external calibration.
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--- Quote ---So what distinguishes a sampling oscilloscope like the HP 54120B or Philips PM3340?
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Back in the old days, Tek used to define1 a sampling scope as a scope that put the sampler in front of the amplifiers and a DSO as a scope that has amplifiers in front of the sampling stage. But this was never an universally accepted definition and wasn't even correct as not all sampling scopes followed Tek's definition (i.e. LeCroy WaveExpert and I believe also the Agilent/Keysight DCA-J/-X). HP also had some sampling scopes (i.e. the 54501A) which didn't follow Tek's rule as well.
Today, a sampling scope is generally considered a fully digital scope that acquires its waveform over subsequent acquisitions to reach its full analog BW. It doesn't matter what sampling technique is used (random or sequential), or how it is actually implemented.
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If the marketing departments of other companies want to confuse the issue, that is up to them. One reason they did so is because sampling oscilloscopes were traditionally difficult to use which is why the Tektronix 7S14/5S14 were designed with a built in delay line which is the primary thing limiting their performance. The delay line was either external or optionally built into later Tektronix sampling oscilloscopes. The Philips PM3340 has a delay line as well limiting its bandwidth to 2 GHz but making it much easier to use.
The HP 54501A is just another digital storage oscilloscope with analog triggering, a bandwidth of 100 MHz, and a sample rate of 10 MSamples/second making it comparable to a 2230 or the 11403A being discussed except for the exceptional bandwidth of the 11403A. The comparison with the 11403A is apt because both HP and Tektronix fell into the "one big knob" user interface trap at that time. In the future, one big knob will control everything!
The definition that Tektronix used has the virtue of being less confusing but even they later limited it to the product descriptions instead of the product names leading to things like "communications signal analyser", "digital signal analyser", and "digitizing oscilloscope" which could mean anything including a 7104 with a digital camera or a scan converter.
So what distinguishes the performance of a sampling oscilloscope from your examples? Overload recovery time is one. Sampling oscilloscope have no overload recovery time which is very useful or even indispensable for some measurements. If I want the best overload recovery time, then I want a sampling oscilloscope no matter what they are calling it today. Picotech makes some and they even call them sampling oscilloscopes. Everything else they make is unambiguously real time but some of their Nyquist bandwidths are not much higher than their input bandwidths; I much prefer ETS support when that is the case.
shteii01:
I have 11403 (not A) with 300 MHz plugin for personal use. I have not done much with mine simply because of being busy.
Interesting side note. I know from Tek Wiki about 1989 date. But I also looked at the Tek catalogs and 11403 does not show in 1989... If I recall correctly it first shows in 1991 or '92.
edavid:
--- Quote from: David Hess on August 21, 2017, 05:51:12 am ---That is right; the 11403A shown is not a sampling oscilloscope. Those vertical amplifier plug-ins are not sampling heads; they are an improved version of the 7000 series vertical amplifier plug-ins.
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Except for the 11A81 3GHz "presampler" vertical plugin.
(Does anyone know the presampling rate?)
Jay_Diddy_B:
Hi,
I have a couple of DSA602A in my collection. They were probably the peak of this series of scopes.
Here is a screen shot:
At some point I wrote a C program to convert the image format to TIFF.
The 'A' version had a floppy, the non A didn't.
There were four 500M s/s digitizer, that gave you up to 2Gs/s with interleaving on a signal channel. Memory depth was 32k samples.
I also has 11801 with SD24 sampling heads. This is 20 GHz bandwidth, but 20 M sps.
There were later versions of the 11801 with color displays etc.
Regards,
Jay_Diddy_B
Wuerstchenhund:
--- Quote from: David Hess on August 21, 2017, 08:08:37 pm ---
--- Quote from: Wuerstchenhund on August 21, 2017, 03:34:02 pm ---A digital scope is either a real-time scope (aquires the waveform in real-time) or a sampling scope (i.e. it acquires the waveform over multiple acquisition passes).
--- End quote ---
Great! So depending on the time/div setting and the input frequency content or bandwidth limiting, a DSO could be either. Or maybe all of those DSOs which can operate either way are a myth. That sure unambiguously simplifies things.
--- End quote ---
Nope, that has nothing to do with settings. If a scope's max sample rate is sufficient to fully capture a signal at its rated BW in a single acquisition then it'sa real-time scope, if the max sample rate is insufficient then it's a sampling scope.
--- Quote ---
--- Quote ---Both the 2230 and the 7854 are are analog/digital combi-scopes which both reach their analog BW in repetitive sampling or analog mode only. You're right that none of them are true sampling scopes as they are combi scopes with an analog and a digital mode.
--- End quote ---
The analog capability of these oscilloscope is irrelevant to the discussion. Why bring it up?
--- End quote ---
Because these scopes are not fully digital scopes, they are combi-scopes, and on combi-scopes the digital part is usually kept simple compared to a contemporary digital scope. BTW, these were your examples, not mine.
--- Quote ---And you are flat out wrong. Neither of these oscilloscope are bandwidth limited below Nyquist. The bandwidth for both is independent of sample rate. This is easy to demonstrate by making an RMS noise measurement at different sample rates; lower sample rates which cause aliasing do not change the measured amplitude because the input bandwidth does not change. The same measurement made of a sine wave or any other signal will produce the same result. Some DSOs take advantage of this for their external calibration.
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Yes, for something simple like noise measurement you're right, but then you don't need a scope for that. But that doesn't change the fact than neither of these boat anchors can (digitally) capture a true waveform of a signal at BW limit in a single acquisition. And for a scope, this is what counts.
--- Quote ---If the marketing departments of other companies want to confuse the issue, that is up to them.
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It's not confusing the issue, and it's not even driven by marketing.
This is what Keysight has to say:
Oscilloscopes fall into two groups, real-time oscilloscopes and sampling oscilloscopes (also called equivalent-time oscilloscopes) and it is important to understand the difference between the two types. Real-time oscilloscopes digitize a signal in real-time. Imagine a repetitive AC signal - the real-time oscilloscope acts like a camera, taking a series of frames of the signal during each cycle. The amount of frames the real-time oscilloscope captures depends upon the bandwidth, memory depth, and other attributes that we will soon discuss. A sampling oscilloscope, on the other hand, takes only one shot of the signal per cycle. By repeating this one shot, but at slightly different time frames, the sampling oscilloscope can reconstruct the signal with a high degree of accuracy.
I know that it's difficult to understand if you only know Tek because that's what you grew up with but they don't dictate the rules. Tek's definition back then was just that, something used by Tek based on the products they had at that time. Others however used a wider definition and for what it's worth this is what has been well established in the T&M field.
--- Quote ---If I want the best overload recovery time, then I want a sampling oscilloscope no matter what they are calling it today. Picotech makes some and they even call them sampling oscilloscopes. Everything else they make is unambiguously real time but some of their Nyquist bandwidths are not much higher than their input bandwidths; I much prefer ETS support when that is the case.
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Funny you mention PicoScope, as it seems they, too, disagree with your definition of Sampling Scope:
https://www.picotech.com/download/manuals/picoscope-9000-series-questions-and-answers.pdf:
A sampling oscilloscope is a special type of oscilloscope that uses a technique called sequential time sampling. This type of sampling is best suited to repetitive waveforms or those that are derived from a regular clock, such as serial data streams, clock waveforms and pulses in digital circuits, semiconductor test patterns, and amplifier pulse-response and rise-time tests. Signals like these tend to have very high bandwidths or high data rates. A sampling scope captures just one sample from one trigger event, typically a single cycle of the waveform or clock, and then repeats the process over a large number of cycles, varying the timing of the sample by a small increment from one sample to the next. The resulting collection of samples is then assembled into a picture of a typical cycle.
The advantage of a sampling scope is that even with input signals in the gigahertz range, the output of the sampler is at a much lower frequency, typically in the audio frequency band. This allows high-fidelity, low-frequency amplifiers and ADCs to be used to capture the signal. For example, the PicoScope 9300 Series can capture waveforms up to 20 GHz with high precision (16-bit resolution before scaling and processing). A real-time DSO that could capture a single cycle of the same 20 GHz waveform would be prohibitively expensive. For example the 20 GHz Agilent DSOX92004A, with a real-time sampling rate of 80 GS/s, has a base price of $177,000 — almost 12 times the price of the PicoScope 9301 while yielding only 4 samples per cycle. The PicoScope 9300 Series, sampling at an effective rate of 15 THz, would yield 750 samples per cycle of the same waveform.
A further benefit is that every sample point in the sequential sampling process is timed from the trigger event, and therefore from the original signal, rather than derived from an internal oscillator. Sampling jitter is therefore vastly reduced compared to the singletrigger, clock-derived sampling of the real-time DSO counterpart.
As I said, I understand where you're coming from but there's no point to fixate of a some 30 years old definition by a single manufacturer while constantly refering to ancient kit that has long been obsolete when the rest of the world has moved on.
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