[HN Gopher] The Mysterious 50 Ohm Impedance: Where It Came from ...
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The Mysterious 50 Ohm Impedance: Where It Came from and Why We Use
It (2021)
Author : amelius
Score : 97 points
Date : 2023-05-28 19:50 UTC (3 hours ago)
(HTM) web link (resources.altium.com)
(TXT) w3m dump (resources.altium.com)
| userbinator wrote:
| 300 ohms is also very common in applications which use
| https://en.wikipedia.org/wiki/Twin-lead
| myself248 wrote:
| For even lower loss, ladder-line is available in 450 ohms.
| kmbfjr wrote:
| Which is the only replaceman open-wire feeder at 600 ohms.
| They don't make it any longer, you're on your own to
| construct it or make-do with ladder line.
| howard941 wrote:
| Yes you can definitely build your own ladder line. The
| insulators are available. But it's probably easier to use
| window line [0] instead.
|
| [0] https://www.trueladderline.com/blog/window-line-open-
| wire-fe...
| mordae wrote:
| The article is not that good, but whatever.
|
| I am new to electronics myself and quite fascinated how has the
| art progressed in the past hundred or so years. There are people
| remembering "we were doing it wrong". Incredible.
|
| Anyway, if you are interested in signals traveling inside those
| cute green multi-GHz boards you make your living off, go watch
| Rick Hartley.
|
| https://www.youtube.com/watch?v=ySuUZEjARPY (How to Achieve
| Proper Grounding)
|
| https://www.youtube.com/watch?v=QG0Apol-oj0 (What your
| Differential Pairs Wish You Knew)
| kurthr wrote:
| I like Rick. At least they got that it was the original coax
| cables that drove it. Then once you have lots of measurement
| equipment and cables, it's hard to change (even SMA is 50ohm).
|
| You can still get 75ohm BNC cables (close to 77) and 93ohms
| (and I think some 150/300ohm antenna cables?). Once you get
| over a few GHz all the inputs are balanced differential anyway
| and you have T networks to optimize power reflection.
|
| It doesn't mention at all that free space impedance that
| matters a lot to actual aerial antenna design is 377ohms. I
| don't know enough about it, but assume they're using
| transformers to balance loads (about 300ohms?).
| bowsamic wrote:
| Electronics has and likely always will feel like arcane magic
| to me
| pclmulqdq wrote:
| High-speed digital and RF are more "magical" than a lot of
| other forms of electronics. It is quite a bit more
| approachable if you limit yourself to ~200 MHz signals at
| most, then you don't really have to worry about the RF
| properties of your circuits as long as you keep the wires
| pretty short.
| [deleted]
| nomel wrote:
| It's a beautiful demonstration of how increasing one
| parameter (frequency) can successively invalidate whatever
| model you're using for the system, where negligible errors in
| the model eventually become functional circuit components.
| akiselev wrote:
| That's why one of the best books on high speed digital
| electronics is titled _High Speed Digital Design: A Handbook
| of Black Magic_ [1]
|
| [1] https://www.amazon.com/High-Speed-Digital-Design-
| Handbook/dp...
| timemct wrote:
| Especially when you think about what electronics are made of:
| things mined from the earth. They made rocks compute for us!
| charcircuit wrote:
| Where else would they come from, the moon? It's to be
| expected that for large scale products like computers to be
| made from common materials.
| [deleted]
| al2o3cr wrote:
| My favorite bit of "electronics magic":
|
| https://www.youtube.com/watch?v=PD7DzTIFJdU
|
| (this has more to do with TFA and impedance-in-general than
| might meet the eye at first glance)
| BenFranklin100 wrote:
| Get this book:
|
| https://www.opencircuitsbook.com/
|
| It's a book featuring macro photographs of cut-aways of
| electronic components. It's the first book that helped me
| really think of electronic components as a physical things
| whose function followed from physical principles, rather than
| an arcane collection of various bits of black magic strung
| together.
| CliffStoll wrote:
| Windell Oskay & Eric Schlaepfer's book has brilliant
| photographs and insightful text ... a coffee table book to
| delight any techie. They slice through connectors,
| semiconductors, and components ... showing the wonderful
| microscopic world of everyday electronics. A real joy!
| fxtentacle wrote:
| Just a quick comment on the product, since this it effectively an
| ad for Altium.
|
| They typically present themselves as the most popular solution,
| but they also very clearly out-price any hobbyist at $10k for a
| perpetual licence. Their "hobby" version CircuitStudio lacks
| critical features and has 0 support and 0 updates and the forums
| are just crickets. But KiCad is free, open source, and looks
| similar enough that I had a great time following the Altium
| tutorials by Rick Hartley with it.
|
| In my opinion, that also invalidates their claim that Altium is
| the most commonly used PCB design software, because there likely
| are 100x more hobbyists using KiCad than people able to spend
| $10k on a hobby.
|
| It seems to me like Altium is developing like Eagle. They used to
| court the makers and hobbyists and then greatly profited when
| those people started working. But now both of them are mostly in
| the business of milking companies who have existing data in their
| proprietary file format.
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(page generated 2023-05-28 23:00 UTC)