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I just bought an HDMI repeater and had connectivity issues until I realized the repeater had to know the cable length. It has (1,2,4,8) dip switches that you have to use (binary coded) to set the cable length.

What I'm wondering is: How is the cable length important? If it was just a question of power/loss over the cable, wouldn't the stronger setting always be the best? I assume that since the length is required it either has to do with capacity or signal echo bouncing back the cable end.

Technical details would be enlighting.

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    \$\begingroup\$ Might be a setting for pre emphasis \$\endgroup\$ – PlasmaHH Nov 27 '17 at 16:31
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    \$\begingroup\$ Even if it was just a matter of simple signal amplification, then signal too strong would overdrive the receiver, which is never good. \$\endgroup\$ – Agent_L Nov 28 '17 at 14:36
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Some repeaters have a model for the frequency-dependant characteristics of the cable (which varies with length), and pre-emphasize the signal in the output driver to compensate for those characteristics so that the signal at the far end comes closer to the ideal waveform. Such a driver can drive a longer length of cable than an uncompensated driver can.

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