Back to Basics: HD over Coax
In its 2017 Video Surveillance Trends Report, IHS Markit forecasted that shipments of HD CCTV cameras would grow to nearly 29 million units globally in 2017. While HD CCTV technology – which enables users to receive HD video surveillance footage over their existing coaxial cable – barely existed in 2012 at all, high definition (HD) over coax has risen dramatically to serve as an economical alternative to IP network video, delivering up to seven times more resolution than the standard 640 x 480 analog camera.
“Many of the initial barriers to its adoption have been resolved or are in the process of being resolved,” Jon Cropley, Principal Analyst for Video Surveillance at IHS Markit, explains in the report. “HD CCTV equipment has a low price; it offers a much greater cable reach than early products; recorders are now available that can record in multiple formats such as analog, IP and competing HD CCTV formats; higher resolution cameras are being launched including 4K cameras; and power over coax (PoC) is coming soon.”
In the end, analog CCTV applications that require an upgrade can leverage HD-over-coax as a cost-effective backbone that enables a simple installation without the need to replace the analog infrastructure, or to upgrade incrementally for an overall cheaper system. With more than 400 million analog cameras currently in use throughout the world, upgrading the resolution of entire legacy CCTV networks can be costly. HD-over-coax solutions allow for the fundamental components – including the DVR, cameras, and 75 ohm coaxial assemblies – to remain unchanged.
Many HD-over-coax systems also leverage bi-directional data transmission, which drastically reduces the amount of cabling. In the future, power over coax (PoC) will also cut out the power distribution often necessary for many CCTV systems, further simplifying a camera installation. The long transmission distance is a major benefit that HD-over-coax has vs. Ethernet, which often requires fiber optic runs for long-range outdoor security applications.
HD-over-coax essentially allows for interoperability with legacy systems while extending the length of the cable to monitoring equipment. This effectively maintains the same level of security while upgrading the resolution and frame rate of video footage. Today’s DVRs can record in analog, IP and HD CCTV formats. Current cameras can accomplish 5MP HD-TVI and 4K video resolutions while maintaining backward compatibility with analog systems – thanks to increased compression efficiency.
As you walk the show floor at ISC West, you will encounter plenty of examples of HD CCTV technology. A vast number of vendors offer HD cameras and compatible DVRs and monitors with coaxial interfaces – with HD-over-coax technologies including AHD, HD-CVI, HD-SDI and HD-TVI. Let’s take a closer look at what you need to know about each technology before you hit the vendor booths.
How HD-over-coax Works
The traditional CCTV network passes video data captured by an analog camera through a coaxial cable to a monitor DVR for real-time video streaming. The DVR is mainly leveraged as a storage device to permanently capture live feeds via a SD card or a disc, where videos can be accessed by event, time, date and camera. These devices can also connect to networks such as telephone lines and local area networks (LAN) for remote access to security footage.
Many IP cameras upload videos directly to the cloud for convenience and allow users to review footage for a monthly fee – still, local storage offers more control and privacy. Previous camera technologies such as CIF and 960H often use charge-coupled device (CCD) image sensors with a maximum resolution of 700 TV lines (TVL), while HD technologies use progressive scan CMOS image sensors for 1080P resolution.
Both sensors convert light into electrons; however, CMOS-based technology consumes less power, has higher noise immunity, and is already a vastly matured and heavily utilized transistor – so the fabrication costs of these chips are relatively low. This helps in dropping the price of HD cameras close to traditional analog cameras to ease the switch to an upgrade in resolution.
High definition over coax is accomplished typically using RG6 or RG59 coaxial cables with a nominal impedance of 75 ohms. The RG59 cable has an American wire gauge (AWG) of 20 AWG whereas the RG6 has a larger 18 AWG – the lower the gauge, the thicker the copper conductor. The thicker RG6 offers a lower insertion loss than the RG59.
Since insertion loss is a parameter that measures the power lost through the transmission line (coax), the RG6 can carry signals over a longer distance. The benefit of having a thinner center conductor is that the cable can function up to higher frequencies. Where the RG6 generally functions up to 1 GHz, the RG59 can go up to 5 GHz. This is not necessarily pertinent in video surveillance applications but should be noted.
The term ‘RG’ stands for radio guide and is legacy terminology that comes from the military. It is essentially just a standard form factor for coaxial cables that defines the inner conductor, dielectric, and outer conductor diameters as well as the respective attenuations (a.k.a.: insertion loss) to expect. Coaxial cables can also be referred to by the outside diameter – 75-1, 75-2, 75-3, 75-4 and 75-5 – which all denote the impedance of the cable followed by the nominal outer diameter. For instance, the RG59 cable can often be referred to as 75-6; a 75 ohm cable with an approximate 6 mm outside diameter.
The cable is often fitted with BNC connector heads. These connectors can handle pulse powers up to 100 W and often function well into the C-band. The primary advantage of using these particular RF connector heads comes from their ease of installation. The keying mechanism allows for a simple twist to electrically mate connectors as well as maintains a mechanically sound connection that does not come loose due to vibration.
Video baluns, or BNC-to-UTP adapters, enable coaxial cables to be replaced by category 5 or category 6 Ethernet cables. Active video balun transceivers enable longer link distances, upwards of 1,500 meters. This solution can be more cost-effective than running more coax, depending on the mating interface of the camera.
IP vs. Analog Cameras
Ethernet-based IP cameras are growing much more rapidly than HD-over-coax in a variety of applications – including factory automation, and in smart cities where deep learning algorithms are allowing for pattern analysis. Most new deployments are IP.
The IP camera operates as an independent image-processing unit with resolutions as high as 5MP. This means that these cameras can be used as standalone entities, while all video captures are uploaded to the cloud – where complex data processing can occur. Power over Ethernet (PoE) also eliminates the power distribution box, as four of the eight Ethernet wires are used to send power the camera.
Analog cameras can still accomplish high image resolutions without the need change nearly every component in the video surveillance signal chain. HD-over-coax also allows for longer cable runs with passive cabling while Ethernet is limited to 100m (328 feet).
Furthermore, power over coax (PoC) technology – expected to be available in the near future – will carry both the video signal and power over the coaxial bus. This technology may extend the window in which coaxial interconnect is used for video surveillance systems, since IP-based systems often use the convenience of power over Ethernet (PoE) as a selling point.
Comparing the HD CCTV Technologies
There are four primary HD-over-coax technologies: Analog High Definition (AHD), High Definition Composite Video Interface (HD-CVI), High Definition Serial Digital Interface (HD-SDI), and High Definition Transport Video Interface (HD-TVI).
AHD technology was originally developed by Nextchip, a Korean design firm that makes chipsets for the video security market. It supports data transmission over both coax and unshielded twisted pair (UTP) over a maximum distance of 500 meters through the use of equalizers.
AHD can transmit uncompressed real-time images at 30 frames per second (fps) over long distances using advanced compression algorithms and signal filtering.
AHD does not support PTZ cameras, menu controls, and remote focus/zoom lens control, making it arguably less desirable than other options.
HD-SDI: Serial digital interface (SDI) was first standardized by the society of motion picture and television engineers (SMPTE) in 1989. The high definition version was released in 2010 as SMPTE 292M, where the 720P resolution is defined by SMPTE 296M and the 1080P resolution is specified in SMPTE 274M. The original bit rate for standard definition SDI was around 300 Mbps while HD-SDI is around 1.5 Gbps.
With chipsets from a number of major manufacturers including Semtech, Intersil and Texas Instruments, HD-SDI has a high degree of vendor diversity. Similar to many HD-over-coax technologies, the transmitter receives video data from the CMOS sensor as well as audio data and serializes it into an SDI format. Different forms of compression algorithms can be used along with equalizers in order to achieve longer cable reaches.
Since SD-SDI’s release in 1989, the technology has matured in the video surveillance industry. This means upgrading to HD-SDI is relatively simple to integrate, generating a true plug-and-play system. On the negative side, the unidirectional signals for camera control do not allow for changes in camera settings. This requires a separate connector to be built in for more flexibility.
HD-CVI: Originally developed by Dahua Technology, HD-CVI can accomplish up to 500-meter transmission distances and 1080P resolution. The technology supports up to 960H analog cameras for standard definition as well as 1080P HD-SDI cameras for a wide range of compatibility. HD-CVI also has bidirectional control signals and is able to transmit both video/audio and camera control over one coaxial line. This technology is significantly more cost-effective than HD-SDI but was proprietary and only sold by Dahua until recently.
HD-TVI is an open technology developed by Techpoint, a semiconductor company. The HD-TVI 2.0 technical specification was released in 2014 and was quickly adopted by tier one video surveillance manufacturers, such as Hikvision, AVTech, IDIS, TVT and others.
The primary benefit of this technology over HD-SDI is associated with the ability to transmit over 500 meters with uncompressed HD video using cost-effective UTP coax. There is also bidirectional transmission of the control signals, allowing for more camera control flexibility.
HD-TVI and HD-CVI are similar in cost and quality of image. The main difference between the two is that HD-TVI is an open source technology open to third party vendors; while Dahua was the sole manufacturer of HD-CVI digital signal processing (DSP) chips for a few years. However, Dahua has now released the technology to select manufacturers.