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Long Distance Running: The Truth about Signal Extenders

It’s Sunday afternoon; the service went well, except for the new projector. The picture was bright and crisp but kept dropping every other minute. Was it the new “Cat5 range extender” you bought? The seller promised it worked with “any standard Ethernet cable”, but now they say your wiring must be bad.

The company that installed your wiring says it tested fine.

What are you supposed to do with the 200 feet of cable buried inside the ceiling and a projector which proudly reads “no signal”?

Why Extenders are Necessary

Cables like HDMI or Firewire are little marvels of technology. They push lots of data quickly, connect in a snap, cost little, and weigh next to nothing. The downside? Once you go over 15 feet or so, problems start to arise.
Things seemed easier in the “analog days.” Every signal weakens over distance, but analog sound or picture degrades gradually, so you could get away with a softer or dimmer image. If your microphone cable is long, you just need to push the gain a bit.

Digital information faces the same obstacles inside the cable, but the consequences are dire. Digital equipment uses a component known as a “slicer” to decide whether the incoming signal is a zero or a one. When it works, you get a pristine image. But if the signal is too poor, the slicer’s decisions are wrong and the information gets corrupted. The result is intermittent dropouts, artifacts, or loss of signal altogether.

This is where extenders come in: they use various methods to go beyond the original specifications, travel the distance, and arrive at the destination in good shape.

The Problem – What stands between you and your signal?

While a full technical overview is beyond the scope of this article, it helps to be familiar with the basic phenomena that occur inside every cable.

ATTENUATION

Cables carry electrical energy, and that energy weakens over distance as it is absorbed in the conductor and the environment. In analog video, attenuation shows as a darker image with less contrast; in the digital realm the 1’s start to look more like 0’s, and you get nothing

HIGH FREQUENCY LOSS

Modern signals carry a staggering amount of data. What goes through a DVI connector is enough to fill up a DVD in 10 seconds. Lots of data requires high frequencies, and these get lost first. Like looking at an object from afar, you still see the overall shape but the fine details are gone. This is why high definition video is harder to transmit than standard definition

INTERFERENCE

Our world is full of sources of electromagnetic energy. Sooner or later, every cable starts behaving like an antenna and picks them up along the way. It may be radio signals, a power line, fluorescent lights, or natural interference from the atmosphere – they all make it increasingly harder for the device to tell your signal apart from the noise.

CROSSTALK

In order to transmit more information, many cables carry multiple wires – crosstalk is interference between those wires.

SKEW

When using a cable with multiple wires, data is split between them. It is imperative that the signals reach their destination at the exact same time in order to put them together correctly. When they don’t, skew occurs. Skew is common in twisted pair wires such as network cables

The Solutions – Getting from A to B

BETTER CABLE

Not all cables are created equal. The ones that can handle longer distances are better constructed, use better shielding and purer materials, but above all, have thicker conductors. Signal loss depends on wire thickness, and more copper in the cable means slower loss.

Pros: simplest setup, no extra devices or connections.

Even the priciest cables typically cost less than any other solution.

Cons: limited range. Better cables can only slow down the signal’s degradation, not improve it. Rigid and bulky, which can be an issue inside walls. It’s a gamble: an expensive or hefty cable may mean more copper – or more plastic.

REPEATERS

Also called “active extenders” or “line amplifiers”, repeaters boost your signal to allow longer runs. Some multiply the possible distance by 5 or even 10 times. Others only double it but can be daisy-chained along the run. Several models look more like extension cords, with a compact amplifier built into the receptacle.

Pros: Good repeaters have additional controls that counteract attenuation and frequency loss. They restore brightness and sharpness (in analog) or allow longer runs (in digital).

Cons: You are still bound by the limitation of the cable type and many consumer connectors are notoriously flimsy.
Imagine running several HDMI or Firewire extenders inside a sealed wall; what happens if one connection comes loose?

BALUNS

“A balun is a little adapter,” explain Chris Kopin, VP of development at Kramer Electronics. “It is used mostly for composite video or audio and allows you to run over a twisted pair cable.” In the signal extender world, ‘twisted pair’ refers to modern network cables, also known as Ethernet, RJ-45, Cat5 etc. Although designed for computer networks, their unique construction inherently resists interference and has made them a favorite in the signal extender world. Furthermore, they’re thin, flexible, cheap, easy to run, and ubiquitous.

In fact, you may already have them installed at your facility.

Kopin notes that “the term is often misused.” Baluns are passive devices which simply adapt the signal but do not reinforce it. More sophisticated devices are sometimes incorrectly referred to as baluns.

Pros: inexpensive, require no power.

Cons: a balun can work for audio or composite video, but “it really doesn’t work in a high resolution world. There you really need active devices.”

TWISTED PAIR (TP) CONVERTERS

These popular products go by any number of names, but all share the same premise – combining the benefits of baluns and line amplifiers. Like baluns, they convert your signal to twisted pair wiring, and like repeaters, they use active circuitry which allows you to send sophisticated signals over hundreds of feet.

TP converters are available for just about any cable format in existence – analog audio, composite video, DVI, HDMI, Firewire, USB, SDI, and the list goes on. Popular manufacturers are Kramer, Extron, Gefen, and Avocent. Each employs its own proprietary technology in an effort to squeeze the best quality into the cable and recover it at the other end.

Note: TP converters use network cables but have nothing to do with networks. If you accidentally plug one into the other you might bring your network down and even damage either device.

Pros: Good quality and excellent versatility.

One converter at the source and one at the destination simplify the installation.

Cons: You get what you pay for, and good converters are often more expensive than any of the previously-mentioned options. In extreme cases, the converter will cost you more than the equipment it connects.

FIBER CONVERTERS

These may be considered the “gold standard” of signal extenders. Like TP converters, they take your signal and encode it into a better kind of cable. Instead of electricity, the signal becomes a beam of light. Optical fiber can carry signals even miles away with little or no degradation.

A fiber-based solution might cost less than you think.

The converter units are pricey but the fiber itself is not, which makes it cost-effective for long distances. “Fiber is always my recommendation when going from one building to another,” Kopin says.

STREAMING DEVICES AND “OVER IP” EXTENDERS

An over-IP converter is more than a signal extender.

It is essentially the same as the equipment you’d use to stream a sermon over the internet, except that it stays inside your local network

Pros: These devices do plug into any network port, so you don’t need dedicated wiring. The added flexibility means you can hook both the transmitter and the receiver Anywhere in your network, and easily relocate them if needed. If you’re adventurous you may even be able to rig a wireless transmission using cheap Wi-Fi routers.

Cons: Your computer network has to share the road with your video, so both compete for bandwidth. Your internet may be slower or the video quality will fluctuate.

Also, in order to live within the network specs, video will almost always be compressed, unlike any other

Solution in this article. Good compressors are extremely expensive and all of them degrade your signal. In addition, encoding introduces delay which may cause your display to be out of sync with the sound system.

Summary

Signal extenders are powerful and often essential tools to bridge today’s high-quality interfaces with your installation needs. However, they are not flawless plug-and-play devices. With careful planning and proper installation, they can help you spread the gospel anywhere, bright and clear.

SIDEBAR

Video Signal Extenders

Tips:

Choose your cable carefully. Beyond 150ft. “the cable is critical,” Kopin says. Kramer’s tests have found that the same set of transmitter and receiver allowed between 115 ft. and 280 ft. depending on the cable.
Many wiring vendors specialize in computer networks and are not familiar with signal extenders. Since those products push your wires beyond their intended design, your vendor may not take responsibility for any problems.

Consider buying the cable from the same company that makes the extender. This way one company handles the complete signal chain from origin to destination. Kopin: because of the large variations “if you want me to absolutely guarantee a specific distance, then you have to use my cable.”

If you’re installing new wiring, run the best cable you can afford: preferably fiber or Shielded Twisted Pair (STP). STP cables add a metallic shield that protects against interference. Good converters support them, and they’re backwards compatible with the common unshielded UTP connectors. Kopin offers this piece of advice: “If someone calls our tech support with a digital product, wondering why their image is cutting in and out, the first question we’ll ask them is how far are you going and what type of cable did you use? Invariably it’s always UTP. STP is not a requirement, but we never know the type of environment that the product is going into, and to be on the safe side I would run shielded cable.”

If you have the opportunity to run new wiring, just install a few network jacks in strategic locations. You can later obtain the right TP converter for your signals. Kopin suggests running skew-free cable for analog needs and shielded Cat6 for digital.

Budget for the whole signal path. Don’t strain your budget to buy the best projector without accommodating a good wiring solution.

Do not commission a system without thorough on-site testing. An extender may work perfectly in the lab, at the store, with a different cable, or for someone else, but every situation is unique. You may have power lines you can’t move or preinstalled wires you have to work with. The only way to assure everything is working right is to test it in the actual environment. If your signal is critical, use fiber.

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