In order to minimize signal loss and maintain placement flexibility, experts recommend keeping hdmi cable lengths below 20 feet. However, the maximum reliable length for passive hdmi cables that still maintain good signal transmission is generally considered to be 25 feet. This specification increased the maximum bandwidth of HDMI cables from 10.2Gbps to 18Gbps. Most HDMI cable options on Amazon have far fewer incremental length choices, Conclusions based on experimental observations: 1. Length of HDMI cable not critical for apple tv connectivity. 2. Quality of HDMI cable is the limiting factor. Although, I paid $80 for the bad one and only $25 for the one that works with my apple tv. 3. An HDMI cable that doesn't work with an apple tv CAN work to connect an extra screen to ITEM USED: HDMI Repeater An HDMI cable can run for a maximum length of 25 feet (7.5 meters) without a change in signal quality. If you need to reach farther than 25 feet, you will need HDMI extenders or fiber optic connections to get a high-quality signal. Maximum Cat5e/6 Ethernet Cable Length 492 feet (100 meters) Maximum HDMI® Cable Length 49 feet (15 meters) Input Power 5 VDC, 1A AC Adapter Input Power 100 ~ 240 VAC, 50/60 Hz Encoder Power Consumption 1.4 watts Decoder Power Consumption 1.7 watts Operating Temperature +32 ~ +104°F (0 ~ +40°C) Wireless Transmission Distance: Up to 165ft (line of sight) Note: The transmission distance will vary depending on building layout, electronic interference, walls and partitions, other environmental conditions, and may be much less than the maximum. HDMI Cable Length: Up to 5 meters (Input & Output) Supports 2-Ch PCM stereo audio For standard HDMI cables (HDMI 1.4 and earlier versions) that support Full HD (1080p) resolution, the maximum recommended length is typically around 50 feet (15 meters). Beyond this length, the risk of signal loss or degradation increases, especially if the cable quality is not optimal. Vij4VL.