Getting that HDMI to go a Little Bit Farther (Extenders)
It looks like High Definition is here to stay. I mean, why would anyone want to buy an old fashioned TV, with only 480 lines of resolution, when they can buy a HDTV that will give them 720 or even 1080 lines of resolution? Okay, I'll confess, I bought an old-fashioned TV, just when the HD units were starting to come out and were still pretty expensive. So, guess who's stuck with his old-fashioned TV, and can't justify buying a big-screen?
It looks like HDMI is here to stay too. The High Definition Multimedia Interface has overtaken DVI and every other form of audio/video connection for both home entertainment centers and commercial applications in short-circuit TV or video presentation on flat screens TVs or with video projectors.
The only problem with HDMI is that it is somewhat limited by distance. The maximum distance you're supposed to run a HDMI line is 15 meters or about 50 feet. After that point, image instability and blinking on the screen begins to occur. While I don't know too many people who have living rooms longer than 50 feet, in commercial applications it can be a real problem.
Various manufacturers have attacked this problem and come up with a variety of solutions to it, which allow HDMI signals to be transmitted up to 300 meters or 980 feet. Of course to do this, without maintaining signal quality would be worthless. So, the standard is that these extenders be able to send 1080p signal over that distance.
Why Signal Loss Happens
Signal loss is a normal part of electrical transmission. Voltage drop, which is what signal loss actually is, comes about as a result of the resistance inherent in wire. That resistance causes the same percentage of voltage drop, no matter what the initial voltage was. Depending upon the voltage, wire size and distance, you can actually lose a large amount of voltage or signal.
With the low voltage of digital signals, it doesn't take much signal loss before the signal becomes indistinguishable. However, one longstanding way of battling voltage drop is by boosting the voltage. Even though the voltage will still drop by the same percentage, it will have less impact because the ending signal will still be high enough to be read clearly.
The concept of repeaters has existed ever since commercial radio got its start. Between World War I and World War II, commercial radio as a means of transmitting messages got its start. For long distance communications, an operator, hearing an incoming message, would resend it on to the next station. Electronic repeaters later took over this mundane task. We still use repeaters for telecommunications, television and radio today, only they're mounted on satellites.
Repeaters perform that same function as the commercial radio operators did way back then. HDMI repeaters allow you to connect several HDMI cables end to end, through the repeaters. As the signal comes into the repeater, it is "read" and regenerating as a new digital signal, but without any of the signal loss. HDMI repeaters are effective up to about 100 feet.
HDMI Cat-5 Extenders
Most HDMI extenders work by transmitting their signal over Cat-5 or Cat-6 cables. This requires the individual signal pairs to be separated out and run through impedance matching transformers. The signal is then amplified, before leaving to go out over a pair of Cat-5 or Cat-6 cables. Standard Extenders are effective at allowing HDMI signals to be sent up to 100 feet.
For those where 100 feet isn't enough, extended range HDMI extenders are available. The difference between the short-range and extended-range units is that the extended-range units amplify the signal before sending it over the Cat-5 or Cat6 lines. When it gets to the other end, it is easily read by the receiving unit, and recreated as a normal HDMI signal. Extended range HDMI Extenders can send a signal up to 330 feet.
In addition to standard and extended-range HDMI Extenders, there are also units which both act as extenders and signal splitters, allowing the same HDMI input to be sent to as many as eight separate HDMI TVs. The basis of this unit is the same as
extended-range units, amplifying the signal. That way, when it is split between
various outputs, there is still enough signal to power them all. Four and eight
output units are standard. These units can send a HDMI signal up to 200 feet.
The latest addition to the HDMI extender family are the Wireless HDMI Extenders. These extenders work much like the others, except that they don't send the signal out over Cat-5 cables, but instead, do it over radio waves. The radio signal is limited to 100 feet. However, the real benefit in these units isn't in the fact that they extend the
range, but that there are no wires to run up to a wall mounted TV or ceiling mounted video projector.
The longest range HDMI Extenders are ones where the digital HDMI signal is converted to a digital optical signal and transmitted over fiber optic cables. These extenders have the capability of sending signal up to 300 meters or 980 feet.