HDMI Versus HD-SDI – which cable connection is best?
In part one of HDMI Versus HD-SDI I discussed why the physical connectors for HD-SDI are superior to the ones utilized for HDMI. To sum up, HDMI connections are easily dislodged and once the connection is broken you must often reboot one and sometimes BOTH devices of the connection.
The second reason that HD-SDI is sometimes preferable to HMDI has to do with the length of the cable runs. According to industry specifications the maximum recommended reliable HDMI cable length is about 40 (forty) feet. While several manufacturers sell cables much longer than this, their reliability in providing a continuous signal at an acceptable level without amplification is suspect. With HD-SDI the maximum recommended cable length is substantially greater: 100 meters (or about 328 feet). You can go beyond that length if necessary with signal repeaters (which are just in-line signal boosters).
An HDMI signal is made up of several parts: Video, Audio and Voltage. These three parts all need to fall into a certain range of levels in order for the HDMI signal to be recognized and functional.
Ideally in a perfect world every device would output a signal at a given level and every device that receives the signal would work with whatever level of the signal it receives but with different manufacturers, different equipment and different manufacturing tolerances things do not always work out that way.
Generally a lot of the signal reliability comes down to the two devices that are connected at either end of the cable; in addition the quality of the cable also plays a major role. Primarily it depends upon the signal output level of the camera and the level required on the device receiving the signal from the camera. This acceptable signal level varies somewhat from device to device but the voltage level also plays an important role.
With HDMI there are two things that limit the lengths of the cable runs: the actual signal level and the level of the voltage provide; If either of these falls below the level that the receiving equipment requires then the signal will not get through and you will get no video or audio. The HDMI standard allows for devices to be able to be powered using the voltage provided on the HDMI cable, so you may have a camera providing power to the device it is connected to, which is why the voltage level is so important
Most High Definition broadcast video equipment uses the HD-SDI signal/connection standard. With a few exceptions there is a HD-SDI mini connector (typically a locking push-on type connector) which is used when there is not enough space to accommodate a number of standard-size HD-SDI connections.
Therefore, if given the choice, the best option is the HD-SDI BNC connection type. If it is outside of your budget (or your camera equipment is strictly HDMI and you have to use that connection standard) there are a couple of workarounds to extend the cable length of HDMI cables. The first is to use active cables; these are cables which have signal amplifiers built into them which are powered by the HDMI devices on the ends of the cable. These cables are more expensive than standard HDMI cables, but they can be used up to 100 feet.
Finally, the other workaround is, coincidentally enough, called an HDMI extender. It converts and amplifies the HDMI signal which allows it to be transmitted over common (and relatively inexpensive) category 5 or category 6 networking cable. This does allow you to extend the cable length up to 330 feet, although the downside is you would have to have an extender for every camera that requires a long cable run. The better units can range in price between $300 to $700 depending on their features. Most of these units require power be supplied for the converter at either end of the cable, some however only require power at one end.
So, in summary, while it is possible to utilize HDMI in many applications, HD-SDI is the preferred connection type.
Our Stream Breeze systems employ either connection types depending upon configuration. Because we can customize ANY of our systems we can adapt one for your needs and existing equipment. Check out our full line at Streambreeze.net to learn more.