Dennis Frie

- a couple of projects and pictures


(2013) SPDIF cable measurements (75 ohm)

75 ohm dummy load

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Calculations

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Theoretical reflection vs. impedance

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75 ohm load overview (perfect match)

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75ohm one pulse

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75 ohm risetime
approx 8 ns risetime

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Falltime

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Open load, mismatch, overview.

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Open, one pulse

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Open, risetime.

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Open, falltime

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Setup with
75 ohm source
75 ohm cable
75 ohm load
5 ns delay (1 meter cable approx)

Transfer function with sweep of cable-impedance from 10 - 100 ohm. Worst match is 10 ohm and is the plot with most attenuation.
The 6 dB loss is caused by the "voltage-divider"

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If we look at 75 ohm cable +/- 10 ohm, it's clear that we only have a very limited amount of reflections

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Lets check square-waves with 8 ns risetime, approximately equal to what we saw earlier. Sweeped impedance from 0 - 100 ohm

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10 ohm cable with a cable length sweeped from 1 ns delay to 20 ns delay (approx 4 meter cable)

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Testing with 1000 ohm load, approximately the same as open load in this case, 75 ohm cable and 100 ohm source, this is the result with 10 ns delay in the cable.

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comparing the simulation with the actual measured signal, the reflections are fairly close

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