Long-Distance AV Signal Transmission
How far can a signal go? Not surprisingly, the answer depends on many factors, including the technology that's carrying it. But for runs of more than 300 feet, there are even more issues to consider, including the cost of cabling and labor, bandwidth, and ease of installation.
That problem prompted the industry to create filters that use multiple poles to keep some frequencies from getting too hot. “That's been done on coax for years,” Mortensen says. “But in a perfect scenario, it would be an infinite number of poles to make a perfectly corrected flat curve. That doesn't exist. In the Cat5 realm, we've done something more sophisticated: a seven-pole, complex-state, variable filter. It does a much, much finer correction over cable losses than what's available on the market in Cat5 or coax.”
The signal's strength at the beginning of its journey also determines how far it can travel. That's particularly important with wireless technologies.
“Most microphone transmitters only have 10 to 50 milliwatts (mW) RF output power,” says Joe Ciaudelli, a consultant on the professional products industry team at Sennheiser, based in Lyme, CT. “This is a good level for stage use to prevent overload at the receivers if several transmitters operate in close proximity to each other. However, for long distances, a high-power transmitter rated at 250 mW is recommended.”
The transmitter and receiver antennas also are major factors in the distance that can be reliably spanned. “At the receiver end, an active directional antenna, such as the Sennheiser A12AD can greatly increase the range of the system,” Ciaudelli says. “This antenna has 4 dB of passive gain, plus a 10 dB amplifier, boosting the received signal a total of 14 dB.”
For most AV applications, fiber doesn't require a booster because the signal doesn't peter out as easily as it does over copper. In fact, that's one of the reasons why fiber is widely used for undersea phone lines that span the Atlantic and Pacific oceans.
“Fiber is typically good to several miles,” says Extron's Da Silva. “Fiber repeaters are common, but not inexpensive, allowing signals to be extended hundreds, if not thousands, of miles.”
Depending on the application, it may be possible to mix technologies in order to overcome issues such as cost or distance limitations. “Fiber probably is going to be an increasing market,” says Magenta's Mortensen. “We've seen that starting to come in dynamic signage applications, where people want to go campuswide and run a fiber backbone from multiple buildings and then convert to a copper technology.”
Tim Kridel is a freelance writer and analyst who covers telecom and technology. He's based in Kansas City and can be reached at firstname.lastname@example.org.