4 ms·

Signal Reflection

50 points by ColinWright 6y ago

VectorLock 6y ago
This YouTube video from "Physics Videos by Eugene Khutoryansky" really game me the "ah-ha" moment understanding reflection and impedance matching https://www.youtube.com/watch?v=ozeYaikI11g https://www.youtube.com/watch?v=ozeYaikI11g
stn8188 6y ago
This is part of the field of Signal Integrity within EE - a rabbit hole which I decided to base my career on. For anyone desiring more detail (with some minimal EE knowledge as a prerequisite), two of the most popular texts are: High Speed Digital Design: A Handbook of Black Magic by Johnson/Graham and Signal and Power Integrity - Simplified by Eric Bogatin. https://www.amazon.com/High-Speed-Digital-Design-Handbook/dp/0133957241/ https://www.amazon.com/High-Speed-Digital-Design-Handbook/dp... https://www.amazon.com/Signal-Power-Integrity-Simplified-Prentice/dp/013451341X/ https://www.amazon.com/Signal-Power-Integrity-Simplified-Pre...
- jcims 6y ago
  Not the same but related, I got started down the road of (RF) DSP a while back and just got to the wtf parts, particularly around handling errors, where it really did kind of feel like magic. I couldn’t hack the deep end of the math pool though and tapped out, but the awe remains. ‘The Signal Path’ and ‘w1aex’ are two YouTube channels i still subscribe to for my fix. Watching a waveform on a scope writhe around like a silent theremin when you just move a cable or even wave your hand past it really drives the point home.
xellisx 6y ago
I learned about termination when I had a 10b2 network.
082349872349872 6y ago
Other nice example of reflection at impedance boundaries are the rainbow patterns of oil on puddles, or, well, rainbows themselves.
peter_d_sherman 6y ago
>"Way back in the 70s when I was building logic circuits, I was warned repeatedly that I'd have to get a few things right, or risk "locking up" or "burning out" the CMOS chips I was using. The bogeyman was "Signal Reflection", but no one could tell me what it was, or why it was so bad." [...] >"I remember hooking up a television, again, back in the 70s, and we had to change the cable connecting the aerial, because it was 75-Ohm, and we needed to use 300-Ohm. I was confused. It was wire, and certainly if you connected a meter to measure the resistance, you didn't get 75 Ohms, or 300 Ohms. You got effectively 0 Ohms. It was wire, after all, and wire didn't have resistance. No, but it has impedance. When you have a current flowing down the wire, you have electrons in motion (although not as much as you may think!). And if you have a moving charge, you have a magnetic field. So when you start the current, it starts to create the [temporarily changing] magnetic field, and a changing magnetic field creates a voltage in the opposite direction. So that opposes the current, giving a dynamic [instantaneous] resistance. So starting the current off down the wire causes a [instantaneous] resistance, and we can then talk about how much resistance we experience. That depends on a lot of things, but it serves to show that even just current on a wire is a complex thing." Observation: Changing the current in an existing circuit might not result in an instantaneous change in the current -- that's because an instantaneous change in current results in a instantaneous change in the magnetic field surrounding the current, and an instantaneous change in the magnetic field surrounding a current may in turn act to influence the exact amount of current which can be carried in an infinitesimally short time period... Over a very short, but not instantaneous amount of time, these forces balance, and the current does indeed flow, but that does not happen in an instantaneous / infintesimally small - unit of time... Fascinating!
nudgeee 6y ago
Also check out the excellent video from Bell Labs: “Similarities of Wave Behaviour (1959)” [0], which showcases termination, reflection, resonance and impedance using the Shive Wave Machine. [0] https://youtu.be/DovunOxlY1k https://youtu.be/DovunOxlY1k

50 points by ColinWright 6y ago

This YouTube video from "Physics Videos by Eugene Khutoryansky" really game me the "ah-ha" moment understanding reflection and impedance matching https://www.youtube.com/watch?v=ozeYaikI11g https://www.youtube.com/watch?v=ozeYaikI11g

stn8188 6y ago

This is part of the field of Signal Integrity within EE - a rabbit hole which I decided to base my career on. For anyone desiring more detail (with some minimal EE knowledge as a prerequisite), two of the most popular texts are: High Speed Digital Design: A Handbook of Black Magic by Johnson/Graham and Signal and Power Integrity - Simplified by Eric Bogatin. https://www.amazon.com/High-Speed-Digital-Design-Handbook/dp/0133957241/ https://www.amazon.com/High-Speed-Digital-Design-Handbook/dp... https://www.amazon.com/Signal-Power-Integrity-Simplified-Prentice/dp/013451341X/ https://www.amazon.com/Signal-Power-Integrity-Simplified-Pre...

jcims 6y ago
Not the same but related, I got started down the road of (RF) DSP a while back and just got to the wtf parts, particularly around handling errors, where it really did kind of feel like magic. I couldn’t hack the deep end of the math pool though and tapped out, but the awe remains. ‘The Signal Path’ and ‘w1aex’ are two YouTube channels i still subscribe to for my fix. Watching a waveform on a scope writhe around like a silent theremin when you just move a cable or even wave your hand past it really drives the point home.

xellisx 6y ago

I learned about termination when I had a 10b2 network.

082349872349872 6y ago

Other nice example of reflection at impedance boundaries are the rainbow patterns of oil on puddles, or, well, rainbows themselves.

peter_d_sherman 6y ago

>"Way back in the 70s when I was building logic circuits, I was warned repeatedly that I'd have to get a few things right, or risk "locking up" or "burning out" the CMOS chips I was using. The bogeyman was "Signal Reflection", but no one could tell me what it was, or why it was so bad." [...] >"I remember hooking up a television, again, back in the 70s, and we had to change the cable connecting the aerial, because it was 75-Ohm, and we needed to use 300-Ohm. I was confused. It was wire, and certainly if you connected a meter to measure the resistance, you didn't get 75 Ohms, or 300 Ohms. You got effectively 0 Ohms. It was wire, after all, and wire didn't have resistance. No, but it has impedance. When you have a current flowing down the wire, you have electrons in motion (although not as much as you may think!). And if you have a moving charge, you have a magnetic field. So when you start the current, it starts to create the [temporarily changing] magnetic field, and a changing magnetic field creates a voltage in the opposite direction. So that opposes the current, giving a dynamic [instantaneous] resistance. So starting the current off down the wire causes a [instantaneous] resistance, and we can then talk about how much resistance we experience. That depends on a lot of things, but it serves to show that even just current on a wire is a complex thing." Observation: Changing the current in an existing circuit might not result in an instantaneous change in the current -- that's because an instantaneous change in current results in a instantaneous change in the magnetic field surrounding the current, and an instantaneous change in the magnetic field surrounding a current may in turn act to influence the exact amount of current which can be carried in an infinitesimally short time period... Over a very short, but not instantaneous amount of time, these forces balance, and the current does indeed flow, but that does not happen in an instantaneous / infintesimally small - unit of time... Fascinating!

nudgeee 6y ago

Also check out the excellent video from Bell Labs: “Similarities of Wave Behaviour (1959)” [0], which showcases termination, reflection, resonance and impedance using the Shive Wave Machine. [0] https://youtu.be/DovunOxlY1k https://youtu.be/DovunOxlY1k