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True analog scopes

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adam4521:
I think, to summarise this energetic thread, that ‘true analog scope’ aka CRO has for some time transitioned to heritage technology. If you are a hobbyist, it depends a bit on what form or direction your hobby takes, but for someone learning modern electronics, a DSO is surely the right proposition if you can get one. There are still compromises at the very bottom end, but if you reach for the Rigol/Siglent/Instek/Micsig arena, the machine will be very functional, modern, with warranty protection.

I thought I would make a comment though about the historic significance of the CROs. Everyone who has used one will have cranked the timebase to maximum time, and watched the bright dot process smoothly across at constant speed, left to right, before flicking back and tracking across again.

But now at fast (but not exceptional) timebase of 20ns/div — get your calculator out to check me — the same beam is tracking horizontally at 500000 m/s, a horizontal line speed of more than 300 miles/second! And the thing that remains astounding for me is that it can repeatedly trigger and track the same groove on the screen, with calibrated speed and mm accuracy. Outside of a physics lab, I’m not sure if anything on earth moves that fast!

This humble vacuum tube ‘etch-a-sketch’ enabled us to see and study things in the natural world that were impossible otherwise. It must surely be one of the most significant inventions of the 20th century, shaping our contemporary world, including the world of computers and, of course, making DSOs possible.

So even if CRO is not for electronics any more, the concept, what was achieved with these machines, still worthy of respect. Might help explain why some of us still hang on to them.

joeqsmith:
5" screen, 10 div, 20ns per div or 200ns to travel 5".  That's 25,000,000 in/sec or 395 miles/sec. 

I suspect my first analog scope was maybe 1MHz at best.  As we got faster scopes,  I found myself turning off the lights to see the trace.  We had phosphor storage and our poloroid cameras which I guess helped.  How many of us were triggering the scope with our custom delayed trigger to sequence though the sweep, collecting all those photos, allowing minutes to expose, then digitizing that..... 

Then again, the first DSO we had was a Tek 7000 maybe mainframe.  From my memory, the downtime was more than the uptime. 

Considering used vs new,  a 500 MHz is $5890.   22 years ago, I bought my LeCroy  7200.   I think I paid $600 back then.  I had to hack in a different hard drive.   To be fair, I have had to repair it a few times over the years.   It still runs today and I fire it up from time to time when making videos.   The analog BW is 4GHz.  For non-repetitive waveforms, it has a 500MHz BW and can sample one channel interlaced at 2Gsps.  It has a fair amount of built in math functions along with TDR measurements. 

Then again I'm talking about a product produced in the late 1980s, and I'm sure the scope you mention would out perform it in many ways. 

bdunham7:

--- Quote from: adam4521 on December 20, 2022, 09:17:51 pm ---But now at fast (but not exceptional) timebase of 20ns/div — get your calculator out to check me — the same beam is tracking horizontally at 500000 m/s, a horizontal line speed of more than 300 miles/second! And the thing that remains astounding for me is that it can repeatedly trigger and track the same groove on the screen, with calibrated speed and mm accuracy. Outside of a physics lab, I’m not sure if anything on earth moves that fast!

--- End quote ---

Well, it really isn't 'moving', so there's no limit, not even the speed of light.  A Tek 2465B can move the dot (mostly vertically) over 8cm in 700ps.   That's about 71,500 miles per second or ~0.4c.

tautech:

--- Quote from: bdunham7 on December 20, 2022, 10:55:52 pm ---
--- Quote from: adam4521 on December 20, 2022, 09:17:51 pm ---But now at fast (but not exceptional) timebase of 20ns/div — get your calculator out to check me — the same beam is tracking horizontally at 500000 m/s, a horizontal line speed of more than 300 miles/second! And the thing that remains astounding for me is that it can repeatedly trigger and track the same groove on the screen, with calibrated speed and mm accuracy. Outside of a physics lab, I’m not sure if anything on earth moves that fast!

--- End quote ---

Well, it really isn't 'moving', so there's no limit, not even the speed of light.  A Tek 2465B can move the dot (mostly vertically) over 8cm in 700ps.   That's about 71,500 miles per second or ~0.4c.

--- End quote ---
Which without some form of persistence is arguably of no use to anyone.
It only needs be as fast as we can see which for a repetitive waveform gets multiple writes to the display faster than we can observe.
In a DSO we still have Normal and Single to see and capture these fast events.

David Hess:
The Tektronix 7104 can sweep faster than the speed of light, while at the same time being visible with a single sweep.

https://web.archive.org/web/20110926020847/http://www.oregonlive.com/silicon-forest/index.ssf/2011/09/a_tektronix_oscilloscope_that.html

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