Cable length

The HDMI specification does not define a maximum cable length but because of signal attenuation there is an upper limit to how long HDMI cables can be made.[42] The length of the HDMI cable made depends on the construction quality and materials that were used.[42] The signal attenuation and intersymbol interference which is caused by long cables can be compensated by using adaptive equalization.

HDMI 1.3 has defined two categories of cables: Category 1 certified cables which have been tested at 74.5 MHz (1080i/720p) and Category 2 certified cables which has been tested at 340 MHz (1600p) to reduce the confusion about which cables support which video formats.[43] Category 1 and 2 cables can either meet the required parameter specifications for inter-pair skew, far-end crosstalk, attenuation, and differential impedance or they can meet the required non-equalized/equalized eye diagram requirements.[43] A cheaply made cable of about 5 meters (~16 ft) can be manufactured to Category 1 specifications using 28 AWG conductors.[42] With better quality construction and materials (24 AWG conductors) an HDMI cable can reach lengths of 12 to 15 meters (~39 to 49 ft).[42] The HDMI website has stated that many HDMI cables under 5 meters of length that were made before the HDMI 1.3 specification can work as a Category 2 cable but cautions that only Category 2 tested cables are guaranteed to work.[44] Long cable lengths can cause instability of HDCP and blinking on the screen due to the weakened DDC signal which HDCP requires. HDCP DDC signals must be multiplexed with TMDS video signals to be compliant with HDCP requirements for HDMI extenders based on a single Category 5/Category 6 cable.[45][46] Several companies offer amplifiers, equalizers, and repeaters that can string several standard HDMI cables together. HDMI extenders that are based on dual Category 5/Category 6 cable can extend HDMI to 50 meters while HDMI extenders based on optical fiber can extend HDMI to 100+ meters.[42][47]