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Without amplification, signal strength drops off quickly, noise levels increase and picture stability becomes increasingly difficult to maintain. At this point it is time to consider the alternatives.

There is certainly no shortage, from microwaves and fibre optics to relatively recent innovations such as network video.

But one frequently overlooked option is the humble unshielded twisted pair (UTP). This concept is so simple that it is remarkable so few manufacturers make use of it.

Video over UTP has an impressive number of advantages, starting with its ability to send video signals, without any significant losses, over long cable runs of hundreds of metres without ampli-fication or complex processing.

UTP cabling is cheaper and considerably less bulky than coax. Moreover it has a very high immu-nity to interference and can happily sit alongside cables carrying telephone, data and low voltage power supplies. So what's the catch?

Essentially there isn't one, aside from the need to install transmitter and receiver (or transceiver) modules at either end of the cable run.

But as these two examples from Network Video Technologies (NVT) very ably demonstrate, it couldn't be simpler.

The two devices we are looking at in this Bench Test are the NV-211T-M passive video transmitter and the NV-452R four-port active video receiver.

Small and neat
The NV-211 is a development of the NV-213 passive transmitter module, which we looked at in the August 2001 edition of Security Installer. It is fairly obvious from the photograph that the design has undergone several refinements.

To begin with the compact, almost cylindrical, housing is smaller and neater than its predecessor. Connections to a wide range of cameras have been improved by the use of a short flying lead terminated with a BNC plug.

This arrangement makes it easier to use it with dome cameras, for example, which often have their video output sockets fitted inside the body of the camera housing. On the Mark 1 version you would have needed a short BNC-to-BNC patch cable.

'Passive' means just that: the NV-211 is unpowered and simply connects between the camera's video output and the cable.

When used in conjunction with a matching passive receiver, transmission distances for both video and PTZ telemetry of up to 300m are possible. This jumps to 1km with an active receiver, such as the NV-452R, which we'll come to look at next.

The NV-452 is a four-channel receiver module, housed in a small black rectangular box measuring 184 x 60 x 41 mm, with mounting lugs at either end. A row of four BNC sockets carries the video outputs.

Adjacent to each one is a pair of preset controls for adjusting brightness and contrast and a LED to indicate that a signal is present.

On the left of the unit is a plug-in terminal for the 24 volt AC/DC power supply and a power-on LED. In the middle there is an RJ45 socket for the video inputs and this is wired in parallel with an eight-way plug-in terminal, for the four UTP inputs.

Built-in transient filtration protects the unit and the cameras connected to it from high voltage spikes. 'Ground lifting' helps prevent visible hum bars.

No problem!
When used with an active transmitter connec-tion, NVT claims that cable runs of up to 1.6 kilo-metres are possible. Neither device is going to give installers any problems, though some sort of mounting arrangement for the NV-211 wouldn't go amiss.

It probably won't be a problem for many dome cameras and it can simply fit inside (if there's room) or sit alongside the unit.

But as far as conventional surveillance cameras are concerned, as it stands it has to be allowed to dangle from the video output socket, or perhaps fixed to the side of the camera using double-sided tape or a couple of cable ties, neither of which is very satisfactory.

Otherwise installation is virtually idiot-proof and on both modules it is simply a matter of con-necting the video and UTP cables and hooking up the power supply for the receiver.

   Performance
Basically it does what it says on the box and our somewhat crude tests, repeated from our earlier encounter with this technology, use a relatively short (for UTP) cable run of 250m.

Using a combination of live video and test pat-terns there was no visible degradation in picture quality.

Previous tests we have carried out, using high-grade coaxial cable, have shown a noticeable reduction in image stability and an increase in noise over distances of less than 150m.

What the manufacturer says ...
The NV-211T-M is a universal video transmitter designed to bring the benefits offered by NVT's UTP technology, to any static, pan/ tilt/zoom or dome camera.

Featuring a radical, ultra-compact design, the NV-211T-M supplies high-quality NVT video signals at a much lower cost than was previously available.

Utilising a nine-inch male BNC fly-lead, the NV-211T-M helps to reduce installation times even further, offering a fast-fit, simple solution for connection directly to any camera, and to UTP cable via screw terminals.

Saving as much as half an hour per camera head installation, the NV-211T-M can be used within any internal or external camera housing. Since the transmitter is passive (not requiring a power supply) further cost savings and greater flexibility can be achieved.

When used in combination with an NVT Active Receiver, the added benefits of NVT's ground loop isolation, cross-talk immunity, lightning protection and fully adjustable high and low frequencies mean sharp and clear pictures can be applied to any installed camera, for distances up to 1km.