Re: modulator box

On Sat, 14 Sep 2024 16:10:01 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

On a sunny day (Sat, 14 Sep 2024 08:04:07 -0700) it happened john larkin
<JL@gct.com> wrote in <kj8bej501c9du4djp3afhuhg22dipnibgr@4ax.com>:
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On Sat, 14 Sep 2024 05:56:24 GMT, Jan Panteltje <alien@comet.invalid>
wrote:
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On a sunny day (Fri, 13 Sep 2024 09:11:52 -0700) it happened john larkin
<JL@gct.com> wrote in <uqo8ej5a4nae7qj1m3uij37q67mb5ho75u@4ax.com>:
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https://www.ebay.com/itm/266499095322
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It's 49% off! And even more off from the original price.
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What does it do?

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Generates an arbitrary waveform when triggered, and drives a 2-stage
e/o modulator that was mounted inside. It was used in the NIF fusion
system.

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I I now remember you talking about it here...
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I'm sure the e/o modulator is not inside that one; it's too valuable.
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https://www.dropbox.com/scl/fi/820yum03ge45k0c80buwn/nif-1201-04100_18.jpg?rlkey=3ijtvb3bxmc9c4a9ealpcwffk&raw=1

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Is that their facility?

Yes. I was surprised to find that pic online, with the posters on the
end of the rack.

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https://www.dropbox.com/scl/fi/0b8ltf1hresx8gtfpds25/DSCN0100.JPG?rlkey=qsejza658v8uc9aae6hvh2hnj&raw=1

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That is one way to cool a rack!
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We made the arb waveform by summing 120 Gaussian impuses spaced 250 ps
apart. You can see the Gibbs Ears in the white waveform.
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https://www.dropbox.com/scl/fi/5qf0c0y0627agx4wnwwim/Waffle.gif?rlkey=e8cgrnjli3e5d55wlt4unxjix&raw=1

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Close to rectangular!

The 120 Gaussian impulses were spaced optimally to get a flat-top
rectangular waveform. But if you try to make a square pulse from those
impulses, you get the Batman effect, the ears on either end.

Fortunately, the real waveform doesn't need the sharp corners.

Nowadays, one would just use a screaming fast DAC.

The next-gen modulator uses a Tek arb to make the waveform, and we
post-process that. I had to invent a new way to bias some $300
distributed amplifier chips. DAs are usually specified for telecom
use, where the waveform is DC-balanced data, 8b10b or some such, but
we wanted big short pulses.

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World-class to e-waste in about 20 years.

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Yes, same for most electronics, while back (few years) everybody had to dump their TV for a digital one
Then again here when we moved to DVB-T2 for terrestrial.. Buy a new box...
Now it is new smartphone ever few years?
I was reading some airline will now use starlink sats to gives users access to internet:
https://arstechnica.com/information-technology/2024/09/free-starlink-internet-is-coming-to-all-of-uniteds-airplanes/
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