What our experts say …
Coaxial cable, where would we be without it? CCTV has become so dependent on coax, as a means of moving video signals from point A to point B, that the alternatives can sometimes be overlooked. Coaxial is generally very reliable, moderately robust, it is easy to handle, relatively cheap and 95 per cent of video devices are designed to use it.
In fact it does a lot of things reasonably well, which tends to overshadow one quite fundamental shortcoming: it is not very good for long cable runs, at least not without help from electronic devices, which introduce unwelcome complications and expense.
One of those alternatives to coax is the humble twisted pair, a transmission system so simple, elegant and efficient – particularly in its immunity to interference – that sometimes makes you wonder how we have become so dependent on coax.
Unshielded twisted pair (UTP) devices for video applications have actually been around for more than two decades but the principal advantage – the ability to send and receive complex signals over long distances, without any significant degradation in the quality or increase in noise -has tended to be either unfulfilled, or achieved at the same or greater expense as other systems, such as fibre optics, RF or microwave.
UTP cables are significantly cheaper than coaxial and from the installer’s point of view they are also easier to lay, having considerably less bulk than coax – UTP cable can be up to 1/10 the size of coax.Moreover terminations, connections and joins or junctions are a lot simpler to manage, compared with coaxial and fibre optics.
It can be laid in high noise environments and alongside wire bundles carrying telecom, video, data and low voltage power. This could be significant in new buildings or large scale installations, making lower demands on conduit space, fitting in more easily with existing cable runs and taking advantage of data network topologies.
NVT (Network Video Technologies) claims to have solved most of the major problems of transmitting video long distances over a twisted pair with its range of passive and active UTP transmitters, receivers and transceivers, four of which we have been looking at.
The passive devices are the NV-213A and NV-213A-M transceivers; in fact they are virtually identical except that the 213A-M is fitted with a male BNC connector so it can be attached directly to the video output socket on the backs of cameras and video devices.
The other two products are the NV-653T and NV-652R active video transmitter and receiver modules, which have built-in amplifiers for extended range.
The four devices can be used in a variety of configurations. A pair of NV-213A/Ms will provide a clean link for cable runs up to 300m. With an NV-213 connected to a camera and a NV-652R active receiver attached to the monitor or switching device, cable lengths of up to 1km are achievable and depending on the category of cable used, a NV-653T and NV-652R receiver and transmitter combination permits cable runs of between 1.6 and 2.4km (Cat 2/3 and Cat 5).
In addition to standard video signals, all of the modules can carry telemetry data for controlling PTZ mechanisms and camera functions. Incidentally, the range also includes short-range passive transceivers (up to 150m) plus active and passive rack-mountable transceiver and receiver hubs. All of the devices share a common housing, which is a small black ABS plastic box measuring just 58 x 38 x 25mm. The case is sealed and has mounting plates moulded into either end of the case. The NV-213A/M is a very simple design, having just a single BNC connector for the video input, a pair of screw terminals, labelled ‘+’ and ‘-‘ for the twisted pair connection and a local earth connection.
There is a bit more to the NV-652R active receiver: in addition to the BNC connector it has a pair of rotary trimmers for adjusting optimum brightness and contrast, according to cable length, two LED indicators showing power on and video status, and a set of screw terminals for 24 volt AC/DC power supply and the twisted pair connection. The NV-653T active transmitter shares the same connections, BNC and LED indicators as the NV-652 but instead of the preset adjustments it has a three-position slide switch for selecting cable length and category.
Clearly there is very little here to trouble the installer beyond mounting the units, connecting a short BNC-to-BNC cable from the camera (or mounting it directly on the camera in the case of the NV-213A-M) plus, where necessary, power supply connections for the active modules.
Connecting UTP cables is a rare treat for those accustomed to coax and built-in transient protection and single point grounding should make installations more reliable and less prone to hum loops. The claim on the front of the NVT brochure is simple: ‘Quality video over ordinary telephone wire’. We tried several combinations of NVT modules in side-by-side comparisons with equivalent lengths of coaxial cable video. In all cases the passive and active units performed very well indeed with no significant increase in noise and no loss of stability on 100 and 250m runs.
The coaxial set-up was showing the strain after just 120m with a marked increase in noise and a noticeable drop in image brightness.
What the manufacturer says …
Network Video Technologies (NVT) manufactures CCTV products for the transmission of high-quality, real-time video and audio over unshielded twisted pair cable (UTP). The award-winning NVT product range comprises passive and active single and multiple channel video transmitters and receivers.
NVT’s in-built gain equalisation, ground lifting, and transient protection all contribute to video transmission performance, resulting in a superior quality of signal compared to that when using co-ax. Offering comparable picture quality, UTP video is also superior to fibre for most CCTV installations – due to its lower cost and ease of installation.
The NVT range of transceivers was conceived to tackle the various problems associated with the transmission of quality CCTV video pictures over co-ax and fibre-optic cable networks. Primary applications are for use across medium/large CCTV installations where the bulk and cost of cabling, installation logistics, transmission environment and quality of distributed video pictures may be an important issue.
Virtually anywhere co-ax or fibre is used, NVT’s UTP transmission products can provide a viable and competitive solution, particularly for:
NVT’s patented technology allows more flexible cable routing, with UTP video cables able to reside in the same wire bundle with ringing telephones, Ethernet, 24v AC, RS-422, RS-485 data and other video signals. Even in hostile, high-noise environments such as in travelling lift-shaft cables, next to fluorescent lights or radio transmitters, NVT’s UTP technology provides a secure video transmission solution. Using basic grade telephone cable, with NVT equipment, distances of up to one mile can be achieved without repeat amplification.
