Cable length
The HDMI specification does not define a maximum cable length. As with all cables, signal attenuation becomes too high at a certain length. Instead, HDMI specifies a minimum performance standard. Any cable meeting that specification is compliant. Different construction quality and materials will enable cables of different lengths. In addition, higher performance requirements must be met to support video formats with higher resolutions and/or frame rates than the standard HDTV formats.
The signal attenuation and intersymbol interference caused by the cables can be compensated by using Adaptive Equalization.
HDMI 1.3 defined two categories of cables: Category 1 (standard or HDTV) and Category 2 (high-speed or greater than HDTV) to reduce the confusion about which cables support which video formats. Using 28 AWG, a cable of about 5 metres (~16 ft) can be manufactured easily and inexpensively to Category 1 specifications. Higher-quality construction (24 AWG, tighter construction tolerances, etc.) can reach lengths of 12 to 15 metres (~39 to 49 ft). In addition, active cables or extenders that use fiber optic, and single or dual Cat-5 or Cat-6 cables instead of standard copper can be used to extend HDMI to 50 meters for 1080p and 100 metres or more for 1080i or less. For HDMI over single UTP extender, to be compliant with HDCP requirements, the HDCP handshake signals must be multiplexed with the TMDS video signals. Some HDMI extenders strip off the HDCP encryption to reduce the cost. These kinds of HDMI extenders are illegal to be imported and used in the countries that adopted HDCP standard. Some companies also offer amplifiers, equalizers and repeaters that can string several standard (non-active) HDMI cables together. However, because of the ac ulation of signal skew and clock jitter, the total cable length is limited to around 40 meters no more than two equalizers and repeaters for 1080p. Also, due to the limitation of DDC on which the HDCP is based, the longer cable may cause the instability of HDCP and result in the blink on the screen.