It was a long day in the lab, but I got it working. There are actually four oscilloscopes in this picture: three commercial ones, and one homebrew version on those copper clad boards. Right now, it has the most primitive interface you can imagine - you turn a 20-turn potentiometer to set the time at which you want to sample the input waveform, then read the voltage at that time off a voltmeter. But, even with this insanely stupid interface, it still has a higher bandwidth than the DS1054Z at the back of the table. I measured the bandwidth of the new sampling scope at 156 MHz. Not bad for a first "toy" version.
![](https://cdn.hackaday.io/images/2897621549166939218.jpg)
There are a lot of things to document, and it will take a little while to get it all down, but in a nutshell, I made an adjustable time delay for the x-axis that allows you to move the sample trigger pulse by about 10 ns, with resolution of maybe 30-40 ps (limited by jitter). Using this, I was able to capture a trace of the fall of a 844 ps pulse edge. The 90-10% fall time is 2.41 ns, but correcting for the fact that the input has a fall-time of 844 ps yields a 2.25 ns fall time for the sampler itself. Using the old 0.35/t rule, this front-end has a bandwidth of 156 MHz.
![](https://cdn.hackaday.io/images/1045771549168467591.png)
This plot was created from 79 data points taken by hand. For each one, the delay time was adjusted slightly with the potentiometer, then the voltage was read from a voltmeter. I wrote all the points down on paper. Because of the slow data collection, there's an insane amount of averaging going on. The pulse had a frequency of 1 MHz, and assuming it may have taken me 10-15 seconds to collect each point, there could be 10 million samples averaged to get this result. That's why you don't see any noise.
I think I'll have to automate this before the next test.
![](https://cdn.hackaday.io/images/1578431549167899416.jpg)
Next Up
I have to document the variable delay and pulse generator used to capture this data. But right now I'm tired and am going to sleep.
Discussions
Become a Hackaday.io Member
Create an account to leave a comment. Already have an account? Log In.
This log made me double check that I have liked this project!
PS Struggling with the inductor measurements but it's limited time available rather than anything else.
Are you sure? yes | no
I think you just need lighter coupling to the LC.
Are you sure? yes | no
Yes. I have a bag of shiny new 10M resistors to try and achieve this in one way. Just not got around to opening them!
Are you sure? yes | no