Electronics > Projects, Designs, and Technical Stuff
About ribbon cables at fairly high frequencies.
magic:
This doesn't look bad. I remember testing other non-RF cables like audio and they weren't flat but showed a rising slope, not sure what that would be.
It occurred to me that with perfect source termination the capacitance of the cable doesn't even come into equation because it all gets charged in one round trip time. With 10% overtermination it's still looking very well and easily meets the 30ns settling time requirement.
T3sl4co1l:
I've seen audio cables where the ground is just strands orbiting (helically) around the core, not braided at all. So, essentially zero (magnetic) shielding value... and probably a helical waveguide sort of behavior as far as impedance, velocity and so on. I'm not sure whether that would go up or down with frequency, but it sounds like it will be dispersive.
Also PVC insulation is shite, so it's lossy dispersion at that. :P
Tim
David Hess:
--- Quote from: magic on July 25, 2020, 07:11:18 am ---It occurred to me that with perfect source termination the capacitance of the cable doesn't even come into equation because it all gets charged in one round trip time. With 10% overtermination it's still looking very well and easily meets the 30ns settling time requirement.
--- End quote ---
Exactly, it is the same as any other constant impedance transmission line.
In the example I showed from a Tektronix 2230 oscilloscope, the outer pins are ground and the inner pins are a differential transmission line. The receiver end is single ended parallel terminated into 50 ohms (two terminations) and *no* source termination was used which was pretty common in Tektronix oscilloscopes. At much higher frequencies they used double termination.
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