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Author Topic: 70pS or Bust!  (Read 5134 times)

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Offline JuiceKingTopic starter

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70pS or Bust!
« on: January 25, 2015, 02:45:23 pm »
Two years of patient eBay bottom fishing for a fast pulse measurement system has paid off at last:


Maxed out - 56.1pS rise time

The setup:


Fast pulse measurement setup

Tek 284 pulse generator
Tek 7854 oscilloscope
Tek 7S11 sampling unit plug-in
Tek S-2 sampling head
Tek 7T11A sampling sweep unit plug-in

The 7T11A was the elusive component, but finally I found a reasonable one last week. The 7854 averages the samples from the 7T11A; it's perfect for this application. The pulse generator and sampling head are directly attached with a GR 874/BNC adapter, so there is no coax cable loss.

Together, these cost less than a 100MHz Rigol DSO and needed only minor repairs and adjustment to get (mostly) working. An utter waste of time and money, to be sure, but just amazing to see.

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Offline EV

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Re: 70pS or Bust!
« Reply #1 on: January 25, 2015, 02:59:43 pm »
Quote from: JuiceKing on January 25, 2015, 02:45:23 pm
Maxed out - 56.1pS rise time
Tek S-2 sampling head

56.1ps is quite good value for S-2 sampling head! :-+

Here is rise time with my Tek R7103, S-4 with sampling head extender connected straight to Tek 284 pulse generator.
« Last Edit: January 25, 2015, 03:07:43 pm by EV »
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Offline tggzzz

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Re: 70pS or Bust!
« Reply #2 on: January 25, 2015, 04:06:42 pm »
Why are you confusing time and conductance?

You are measuring time in Siemens (S). The SI unit of time is the second (s).
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There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline JuiceKingTopic starter

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Re: 70pS or Bust!
« Reply #3 on: January 25, 2015, 04:54:49 pm »
Quote from: EV on January 25, 2015, 02:59:43 pm
Here is rise time with my Tek R7103, S-4 with sampling head extender connected straight to Tek 284 pulse generator.

Just when I thought it was safe to go back in the water...
 :D
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Offline JuiceKingTopic starter

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Re: 70pS or Bust!
« Reply #4 on: January 25, 2015, 04:58:38 pm »
Quote from: tggzzz on January 25, 2015, 04:06:42 pm
Why are you confusing time and conductance?

You are measuring time in Siemens (S). The SI unit of time is the second (s).

I, too, thought it looked odd, but I just reported what you see on the screen. Fortunately, no lives were lost in this experiment.
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Offline c4757p

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Re: 70pS or Bust!
« Reply #5 on: January 25, 2015, 05:26:02 pm »
Quote from: JuiceKing on January 25, 2015, 04:58:38 pm
Quote from: tggzzz on January 25, 2015, 04:06:42 pm
Why are you confusing time and conductance?

You are measuring time in Siemens (S). The SI unit of time is the second (s).

I, too, thought it looked odd, but I just reported what you see on the screen. Fortunately, no lives were lost in this experiment.

I'm currently trying to repair a 7854 with faulty ROMs, so I have the ROM images and have to record them to EEPROMs. I...... would not be above trying to find those units in the code and flipping S to s.

That shit really bothers me. ;D
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Offline Martin.M

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Re: 70pS or Bust!
« Reply #6 on: January 25, 2015, 06:02:17 pm »
tell me the Tek No from them, so I can look if they are in the spares box.
I have some ROM for Tek systems but dont know what type they are

greetings
Martin
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Offline tggzzz

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Re: 70pS or Bust!
« Reply #7 on: January 25, 2015, 06:12:25 pm »
Quote from: JuiceKing on January 25, 2015, 04:58:38 pm
Quote from: tggzzz on January 25, 2015, 04:06:42 pm
Why are you confusing time and conductance?

You are measuring time in Siemens (S). The SI unit of time is the second (s).

I, too, thought it looked odd, but I just reported what you see on the screen. Fortunately, no lives were lost in this experiment.

Yeah :( Tek have only "recently" stopped making that mistake!

I know it is unfair, but it is one of the touchstones I use to help me distinguish engineers from wannabies.
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There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline c4757p

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Re: 70pS or Bust!
« Reply #8 on: January 25, 2015, 06:28:07 pm »
Quote from: Martin.M on January 25, 2015, 06:02:17 pm
tell me the Tek No from them, so I can look if they are in the spares box.
I have some ROM for Tek systems but dont know what type they are

greetings
Martin

Probably won't do much good, unless you also have the full patch set, EPROMs (or images) plus FPLA. The ROMs had some relatively minor bitrot, but the EPROMs were quite dead, and I have no idea how to go about programming the EPROM-based FPLA or even if it's possible to get an image out of a working one. I found some ROM images with the patch already applied (pulled via the system bus with a working ROM card), which "should" work with the patching mechanism bypassed (don't know for sure, there's something wrong with the system and I've not yet figured out what).

Anyway, that's the last of my hijack of this thread. I'll probably make one about the 7854 sooner or later, if I don't just make it on the Tek forum.
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Offline wine+dine

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Re: 70pS or Bust!
« Reply #9 on: January 25, 2015, 06:53:30 pm »
Quote from: tggzzz on January 25, 2015, 04:06:42 pm
Why are you confusing time and conductance?

You are measuring time in Siemens (S). The SI unit of time is the second (s).

The Tektronix 7000 series readout system (and quite a number that came after that) don't have a lowercase S.  See http://w140.com/tekwiki/wiki/7000_series_readout_system for more.
In the screen photo posted earlier, the character shape is clearly that generated by the old analog-ROM board, so even if it bothered you, there's no EPROM to change ...
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Offline saturation

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Re: 70pS or Bust!
« Reply #10 on: January 25, 2015, 07:01:42 pm »
Nice, and not many references around to generate < 70ps. The Tek 284 remains a tool worth owning today.  I like your pasted on notes, I too have to be aware of its finicky behavior, it drift with ambient temperature too. 

https://www.eevblog.com/forum/projects/generating-extremely-fast-rise-time-square-waves-for-probe-compensation/msg90410/#msg90410

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