Tech Trends: You Can’t Kill Coax

This legacy technology still serves a major role in both analog and IP video applications

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 they 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 cousins, analog-to-fiber optic transceivers, have also stubbornly resisted extinction. But while these electronic products will inevitably disappear, old transmission media doesn’t have to. It’s easy to see that fiber optic cable can be repurposed to carry any information for which it has the capacity. It’s more of a stretch to think the same about coax, but coax lives on.

Why? Because it’s already in place and it has high bandwidth – generally higher than twisted pair.

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. Much like the fiber transceivers of old, these devices typically used a proprietary format between the remote camera end and its companion device. Users had the option of adding an encoder to an existing analog camera or swapping the analog camera for an IP camera. Because IP camera image quality was often unacceptable years ago, the analog camera may have remained in place. That likely would not be the case today, and a number of manufacturers have entered the fray to offer Ethernet to coax transceivers.

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.

Ronnie Pennington, Altronix National Accounts Manager, points out the cost and performance advantages of this technology, “With the advancements in technology, there is often a need to reuse some of what has already been installed. In some cases, new wire runs are not an option. In other cases, the end users 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 5 times greater than that of CAT5 or higher cabling.”

Guy Apple, Vice President of Marketing for NVT, discusses reliability, “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 un-interruptible power to the edge. 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. How many analog runs over 1,000 feet were employed via coax? However, there are certain restrictions. The coax should be in physically good shape. 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 be taken into account. Ideally, the resistance of the coax should be measured to be sure that it falls within the manufacturers’ guidelines. Resistance can be estimated from charts or measured directly.

You’ll also be safe up to about 1,000 feet for PoE or PoE+ devices from a power delivery standpoint. Bandwidth is a different story. Impedance in copper increases with frequency, and 100 Mbps Ethernet is more demanding than a channel of analog video. Because transceivers convert the data for transmission over coax, their individual specifications must be taken into account when calculating link bandwidth. It will likely be somewhat less than 100 Mbps.

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