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Re: Test input for an SD-32 sampling head


 

Hi, Reg.

Regarding fast pulses and such, there is a wealth of information at Jim
Andrews' page here: He founded
Picosecond Pulse Labs in 1980 and sold it to Tektronix in 2014. I used
PPL products with a CSA803 back in the mid 1990's at Lockheed. I think
the sampling head I used was an SD-24, but since it was about 25 years
ago, my memory is a bit fuzzy.

These days I have a 7904, a 7603, a 7S12, a 7S11, two S-4 sampling
heads, S-53 and S-51 triggering heads, etc in my garage lab. Oh, and a
couple of 10:1 probes I made out of board-edge SMA connectors, 450 ohm
(470 paralleled with 1.8k ohm) 0402 resistors, and 3-pin right-angle 0.1
inch spacing headers. I've not completely characterized the probes, but
at least they pass up to about 12-13 GHz without much attenuation above
the expected 20 dB. Planning to use them to probe some digital RF
boards I'm going to build for work (Raytheon). Too much trouble to try
to get a fast enough sampling scope at work :(

Enjoy the PPL app notes! I've referred to AN-2a through -2e often.

Thanks for the literature references. I'll have to check them out
(someday).

Jim Ford

------ Original Message ------
From: "Reginald Beardsley via Groups.Io" <pulaskite@...>
To: [email protected]
Sent: 3/14/2019 6:03:56 PM
Subject: Re: [TekScopes] Test input for an SD-32 sampling head

I have one of Leo's 100 pS impulse units as a source for initial experiments. If I can narrow that to 10 -20 pS with discrete SMD parts I may be able to get the idea to work. There's a close connection to the Hilbert operator hiding in there somewhere.

I've been reading an excellent book on FPGA implementation of DSP by Roger Woods et al most of the afternoon. So I've not started on the dissertation yet. I can't really say much else until I understand the mathematics and physics of using the reverse biased diodes as capacitors. That should keep me entertained for a few weeks at least.

In any case, failure doesn't matter. It's a hobby project, not a client deliverable. I've been fascinated by the problem of getting a fast rise time edge for a long time. It's a bit of circular logic. My excuse for doing it is I bought an 11801 and my excuse for buying the 11801 is so I could try to do it. If I can narrow the 100 pS pulse by 5x I'll have an excuse to buy an SD-32.

I spent 3 years studying sparse L1 pursuits using "A Mathematical Introduction to Compressive Sensing" by Foucart and Rauhut as a text followed by reading the original papers by Donoho, Candes et al. Beats the hell out of watching television. I just wish I could find someone else who was interested in the subject to discuss it with. It's quite amazing what you can do with sparse L1 pursuits and really easy to do in practice. Understanding the math is not easy, but most people use FFTs without really understanding them.

Have Fun!
Reg


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