NVT PASSIVE AND ACTIVE UTP TRANSCEIVERS
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's easy to handle,
relatively cheap and 95% 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's not very good for long cable runs, at least not
without help from electronic devices, that introduce unwelcome complications
One of those alternatives to coax mentioned a moment ago 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 principle 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 installers
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.
Network Video Technologies (NVT) 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've been looking at for this Bench Test. 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/M's will provide a clean link for cable runs up to 300-metres (1000ft).
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 (3,000 ft) 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 150 metres) 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's a bit more to on 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.
SETUP AND OPERATION
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 250 metre
runs. The coaxial setup was showing the strain after just 120 metres with a
marked increase in noise and a noticeable drop in image brightness.
The modules are very well built, easy to install and setup and the
lifetime warranties suggests NVT are reasonably confident about such things as
service life. Our basic checks suggest that the NVT modules should perform well
in the real world and the cost benefits of the NV-213A/M transceivers should
kick very quickly indeed, possibly on runs as short as 200 metres.
Design and design features *****
Circuitry and components ****
Ease of installation and wiring *****
Range and variety of functions ***
Accompanying instructions ****
Technical advice and backup ??
Value for money ****
ã R. Maybury