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How to make a Smith chart
21–30 of 36 posts
Re: How to make a Smith chart
#22> The Smith chart from electrical engineering is the image of a Cartesian grid under the function f(z) = (z − 1)/(z + 1). More specifically, it’s the image of a grid in the right half-plane. Well, I'm already confused. The domain is complex numbers where the real part is >= 0? I think it would be helpful to make that clear from the get-go. When I see "Cartesian grid", I think R^2, not C.
So you can continue it beyond that circle if you like, it just happens to be the case that the thing electrical engineers and others dealing with waveguides are plotting in the source space, is impedance. (Well, a ratio of impedances—a load impedance divided by a transmission line impedance.) The real part of impedance is resistance, and negative resistance is very uncommon. The area outside the unit circle so mapped, I think also corresponds to reflected amplitude ≤ transmitted amplitude, with the center of the diagram being a perfectly matched impedance, and no reflection.
Re: How to make a Smith chart
#23This is one of my favorite explanations of how to use a Smith chart in practice: https://www.cypress.com/file/136236/download
Also this one: https://www.ti.com/lit/an/swra046a/swra046a.pdf
Re: How to make a Smith chart
#24Is this related to Cardioid patterns for directional microphones?
No. Sorry, that is not a helpful comparison.
Re: How to make a Smith chart
#25I made an interactive implementation here: https://observablehq.com/@mbostock/smith-chart
Really really nice. Thanks for this!
Re: How to make a Smith chart
#26I have PTSD from learning Smith charts in school. My prof even said to me "If you'd pay attention, you'd understand this!". I was the only one who was brave enough to ask questions about it!
Heh, this reminds me, don't worry: One of my extremely intelligent roommates in the 80s switched from EE to CS, seemingly due to Smith charts and Electromagnetics coursework. He went on to make a large fortune in software.
I switched from EE to CS (well, "Computer Engineering" technically) in the late 90s. Not specifically due to Smith charts, but that's relatable. For me it was just realizing that I was procrastinating on doing my EE problem sets, which just started to seem like endless grinding of differential equations, by playing around with whatever we were doing in the couple CS classes I had. I wouldn't say I've made "a large fortune" in software, but it's kept me gainfully employed for a few decades so I think it worked out.
Re: How to make a Smith chart
#27Smith Chart 101: https://www.youtube.com/watch?v=vDU5XnvZXwc
Re: How to make a Smith chart
#28I made an interactive implementation here: https://observablehq.com/@mbostock/smith-chart
Really cool! BTW since you're here, have you checked https://github.com/malloydata/malloy/ and their visualizations? it seems it could be a nice fit for ObservableHQ
Re: How to make a Smith chart
#29Why would you use one?
I remember using these for impedance matching back when I was in college. Basically when you connect two transmission lines (like coax cables), you need to match their impedances so the signal does not bounce back. (Ik this is a gross oversimplification but yeah)
Re: How to make a Smith chart
#30Smith charts look really cool, and they can be really useful for modeling, but for me I can't see the phasors when I use a Smith chart. Myself and all the EEs I work with use bode plots to see mag and phase response across frequency. I know some sick f EEs that just want raw IQ pairs. But Smith charts look sci fi so they're good too.