It’s funny how certain legacy security technologies seem to keep hanging on long past the handwriting of their demise is on the wall — or find new life by being repurposed. A large number of analog cameras have shipped over the last five years, though their share of the market has steadily declined. Their close cousin, analog-to-fiber optic transceivers, has also stubbornly resisted extinction.
While these electronic products are sure to go sooner or later, old transmission media doesn’t have to. It is easy to see that fiber optic cable can be repurposed to carry any information for which it has the capacity — it is more of a stretch to think the same about coax. But coax lives on…why? Because it is already in place and it has high bandwidth — generally higher than twisted pair.
Keeping Coax Relevant
More than five years ago, we began to see the emergence of transceivers that convert Ethernet signals to a form suitable for transmission over 75 ohm coax. Today, a number of manufacturers have entered the fray to offer Ethernet-to-coax transceivers, many providing 48 VDC PoE capability to the camera. Much like the fiber transceivers of old, these devices typically use a proprietary format between the remote camera end and its companion device.
An exciting, relatively recent enhancement is the emergence of PoC (Power over Coax) devices which transfer Ethernet data and power for the remote device over coax. Some remote transceivers provide voltage of 12 or 24 VDC, while others provide 48 VDC PoE. Because power is provided over the cable, there is also no need to separately power the remote transceiver.
“With the advancements in technology, there is often a need to reuse some of what has already been installed,” explains Ronnie Pennington, Altronix National Accounts Manager. “In some cases, new wire runs are not an option. In other cases, the end-user’s budget is not sufficient enough to cover the labor of pulling new wire. Whatever the case may be, new technology also allows us to create products to reuse the existing infrastructure. New media converter/adapters, such as the eBridge series from Altronix, allow us to transmit the latest technology IP video and power over the existing coax cabling at distances up to five times greater than that of CAT5 or higher cabling.”
“Conventional Ethernet repeaters must be installed every 328 feet — for the installer, that typically means IDF closets in odd locations throughout the facility in order to create uninterruptible power to the edge,” says Guy Apple, Vice President of Marketing for NVT. “A camera at 750 feet requires two repeaters. These repeaters and their associated connections all add up to being a potential remote point-of-failure headache.”
In most cases, existing coax plant should be sufficient to implement these solutions; after all, how many analog runs more than 1,000 feet were employed via coax? However, there are certain restrictions: The coax should be in physically good shape; and grade of coax (typically RG-59/U with a 20 or 22 AWG solid copper core), length of run, remote device power needed, and bandwidth requirement must also be taken into account. Ideally, the resistance of the coax should be measured to be sure that it falls within the manufacturers guidelines.
Bandwidth is a different story. Impedance in copper increases with frequency, and 100 Mbps Ethernet is more demanding than a channel of analog video. Consult manufacturer product specifications.
Environments such as retail are great candidates for deployment of this technology. Many have existing coaxial infrastructure and are sensitive to the cost of replacing that with Cat 5e or higher cable. Cable runs are typically not that long and bandwidth requirements are limited, while minimizing downtime is essential.