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Test Equipment Anonymous (TEA) group therapy thread

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tggzzz:

--- Quote from: Specmaster on June 03, 2018, 06:16:08 am ---True, in that case stick to the core function of a scope and hopefully reduce the prices and make the UI better. Most people already have the other items anyway.

--- End quote ---

Marketing droids used to hate it when I asked "would our customers prefer us to do one thing well or two things poorly?". Every such decision on their part exposes them to the consequences of a bad decision.

The consequence of not answering the question is all the "eierlegende Wollmilchsau" which waste our time and money.

bd139:
Marketing droids would prefer two things done poorly as they can cover that up with enough lies and sell two things. Years in “enterprise” software has taught me that. They don’t like me doing product evaluations now as the word lie usually goes in it several times.

Software is very hard to put together. So is hardware to get to the point you’re confident with shipping it without incurring a recall. One reason why everything is shifted into the digital domain. Reduces risk as you fix that later.

djos:
Chaps, question after the recent scope debate, what the hell is a "digital real time scope"?

Uneducated guess is its a DSO minus storage and therefore having the worst aspects of DSO and CRO combined?

bd139:
They’re both sampling scopes. Real time ones are just faster.

Sampling scopes usually use reconstruction ie they pick samples as quick as possible not necessarily on the same wave cycle to sample say a 20GHz signal. This allows you to build an approximation of a very fast signal if it is repetitive.  Real time ones have stupid fast ADCs and ungodly trickery so they actually sample near the full rate.

Berni:

--- Quote from: djos on June 03, 2018, 07:25:42 am ---Chaps, question after the event scope debate, what the hell is a "digital real time scope"?

Uneducated guess is its a DSO minus storage and therefore having the worst aspects of DSO and CRO combined?

--- End quote ---

No it just means that the sample rate of the scope is above the Nyquist frequency of the bandwidth its rated for so that it can acquire samples in real time. These days it might sound like its obvious since all scopes have a higher sample rate than the bandwidth.

But in the old days they did not have the tech to build a 1GS/s 8bit ADC and move around data quickly enough. So they built so called "digital sampling oscilloscopes". These scopes have a ADC that runs slower than the bandwidth of the scope, because they are so slow means they can only grab a few samples per trigger event, but they keep repeating this on different spots in time in the next trigger events to slowly build up the waveform. This is then essentially a digital scope without the one shot trigger advantage that CROs don't have. It needs a repetitive waveform with a stable trigger to show you any meaningful image.

But that sounds like a awful deal. Why would anyone want a digital scope that's missing the main selling point of a digital scope ? Well the answer is speed. CROs are limited by how quickly you can deflect the beam and this gets really difficult once you get to 500MHz. On the other hand digital scopes need ridiculously fast ADCs to to digitize waveforms above 1GHz. But a sampling scope is only limited in bandwidth by how fast of a sample and hold circuit you can put in front of the ADC to grab a sample from the waveform.

I have such a scope. Its a HP 83480A ( https://www.keysight.com/en/pd-48467-pn-83480A/digital-communications-analyzer?cc=SI&lc=eng )
The fact it has HP in the name shows it age. But this scope can show you up to 50GHz of bandwith with the right plugins. I haven't been able to track down those plugins so mine is only limited to 20GHz. This allows you to measure step responses with rise times in the 10s of picoseconds or draw eye diagrams of >10Gbit serial data lines.

These days they are becoming quite obsolete since we now have the technology to create 100GHz bandwidth real time oscilloscopes (If you can afford them that is).

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