ClearOne Digital Media - Manual (Page 73)

Repeaters
One limitation of HDMI is that traditional cables are general only certified for use up to
10 meters in length. However, HDMI technology has been designed to allow standard
copper cable construction at longer lengths but requires the use of a repeater to extend
beyond 10 meters. In order to allow cable manufacturers to improve their products through
the use of new technologies, HDMI specifies the required performance of a cable but not
maximum cable length. NOTE: It is not only the cable that factors into how long a cable can
successfully carry an HDMI signal but also the receiver chip inside the display which also
plays a factor. Receiver chips that include cable equalization are able to compensate for
weaker signals, thereby extending the potential length of any cable used with that device.
It is important to be aware of both active and passive solutions when it comes to HDMI
cables. Whereas a repeater by definition must be active and therefore power supplied to
the device in some manner. Any HDMI device that has active electronics should have a
provision for external power in order to be compliant. Some active devices, such as actively
powered HDMI cables or in-line signal extender boxes, will by default attempt to power their
electronics by taking power from the 5V line (+5V power) available on the HDMI connector.
The HDMI specification requires all source devices to provide at least 55mA (milliamps) on
the 5V line for the purpose of reading the EDID of a display.
While 55mA is not enough current to operate most HDMI accessory devices (which
typically require about 100 to 150mA), most source devices on the market today provide
significantly more current on the 5V line than the HDMI specification requires. As a result,
the vast majority of accessory devices can operate when interfaced with a source device
that provides more than the required current (i.e. over 100-150mA) on the 5V line. However,
it should never be assumed that the source device will provide enough power, and
manufacturers should make a provision for their powered HDMI accessory devices to obtain
external power.
For the AV systems installer and designer, what this means is that failure of video output
when a Repeater is used can often be attributed to a simple lack of adequate power. Just
because a device says it doesn’t need an external power supply, it is advisable to not use
it and select one where you can be assured the product will always have adequate power
regardless of the source that is connected.
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pg 73 StreamNet Digital Media and System Design Reference Guide
Solving Digital Media Related AV Problems