CABLE EQUALISATION AND LAUNCH AMPLIFIERS
WHAT OUR EXPERTS SAY...
The difficulty of sending video information over long distances has
proved to be an enduring challenge for the surveillance industry. As
installations get bigger, with ever more cameras managed by fewer operators,
the problem can only get worse. Over the years numerous ingenious solutions
have been developed, some more successful than others, but whilst a number of
systems have proved to be highly effective under particular conditions, the
vast majority of installations still rely on a cable linking the camera to the
In addition to being the simplest means of connecting two devices
together, a cable has the advantage of being reasonably secure, largely immune
to interference and the influence of surround buildings or local terrain. Cable
is also comparatively cheap and if properly installed, requires little or no
maintenance. Cable is also very reliable but when it does go wrong, it is
(usually) easy to fault-find and repair.
Cable sounds like the answer to every maiden’s (or installer’s) prayer
but there’s a catch. Video signals do not travel well over distances of more
than a few hundred metres. A video signal is a remarkably complex entity
comprising a dense mixture of amplitude and frequency modulated waveforms that
are adversely affected, to a greater or lesser extent, by the electrical
characteristics of the cable they’re passing through. Moreover, on really long
cable runs as the signal becomes weaker the effects of noise also become more
There are various ways around these problems. The two commonest
approaches are to ‘boost’ or amplify the video signal as it emerges from the
camera or during its journey to the monitor, or the signal can be processed at
the monitor end, to compensate for the changes that occur on a long cable runs,
and boost the signal back to its original or optimum level.
That brings us to the subject of this Bench Test, two products from
Tecsec Europe that one way or another make it possible to send video signals
over long cable runs, emerging at the other end in near pristine condition. The
devices in question are the VCE2FS Video Cable Equalisation Amplifier and
VLA2-12 Video Launch Amplifier, which can be used either separately or in
combination with one another.
The VCE2FS Equalisation Amplifier will normally be located close to the
monitor or control/switching devices, though it can also be used as a repeater,
at a point in a cable run determined to be in need of equalisation. It is
available in a range of configurations. The sample we’ve been looking is housed
in a rack-mounting case, which can be fitted in banks of 3 in a standard 2U
frame. The key features include frequency compensation on 75 ohm balanced or
110 – 150 ohm unbalanced (coaxial or twisted-pair) cable runs up to 6km,
variable video gain (-1 to +10dB) it has a built-in video loss detector with
front panel indication and alarm contact. A low band filter and optical
isolation of the input and output signal paths provides a high degree of
immunity to noise, hum and earth current rejection and the input and output
connections have lightning and over-voltage protection. Bandwidth can be
tailored to suit a variety of applications; a 5.5MHz ‘narrow band setup is
recommended for installations with extra long cable runs or where noise is
likely to be a problem. The standard 8MHz option is designed for the majority
of colour and monochrome cameras and there’s a 10MHz wide-band system for use
with higher definition and S-Video equipment.
Models with additional interference immunity, from local or nearby
transmitters, are also available. The unit has a built-in mains power supply.
The VLA2-12 Launch Amplifier is designed to be mounted next to or close
to a camera, providing the signal with an additional boost to improve its
chances of travelling along balanced or unbalanced runs of up to 400 metres.
Improvements in signal quality may be possible – depending on cable type – in
cable runs as short as 200 metres. The module we have been looking at is housed
in a two-tone white and grey ‘Verobox’ type enclosure, it is powered from an
external 12volt DC source and it comes supplied with a mains adaptor.
Rear panel connection on the VCE2Fsconsist of a 3-pin IEC mains socket,
two BNC sockets for unbalanced coaxial video and two spring terminals, for the
balanced twisted pair video input and output, alarm connections are handled by
a 5-pin DIN socket. A small rocker switch is for power on/off. On the front
panel there are three LED indicators showing power status (mains and low power
circuits) and the third one shows video input, flashing when the input is
removed or interrupted. Build quality
is impressive, reminiscent of the proverbial brick outhouse in construction and
clearly designed to be suitable for use in earthquake zones... The standard of
construction is also very impressive; three PCBs are firmly bolted to the
sturdy steel chassis and it’s a little unusual to see what amounts to a mini
wiring loom inside any electronic product these days, but it is all very neat
Video connections on the VLA2-12 are also in the form of two BNC sockets,
and one set of screw terminals for a balanced twisted pair. On the opposite end
there are two DC connectors, for power in and out, and a single power-on LED
indicator. Inside the box there’s a single PCB and once again it has a slightly
old fashioned feel to it with lots of full-size discrete components, rather
than the usual forest of microchips and microscopic surface mount components.
Build quality is generally satisfactory, though some rather sloppy hand
soldering around the video input connections on one of our sample units came
close to preventing the use of some setup link pins on the PCB.
SETUP AND OPERATION
The instructions leaflets for both units are on the brief side and could
do with more detailed illustrations but all salient points are covered.
Installation and setup are reasonably simple, a pair of shorting links
determines whether the video input is balanced or unbalanced and a second
shorting link sets normal (1-volt) or high (3v) video output. Preset controls
on the main PCB, which the instructions warn can only be correctly set with the
use of a signal generator and oscilloscope, are provided for setting input balance,
input impedance (when using a balanced/twisted pair video connection), video
level, low, mid and high-frequency lift).
Setup and adjustments in the VLA2-12 Launch amplifier follow a similar
theme with links for setting coaxial or twisted pair output, video level (-1 to
+10bB), high-frequency lift and output balance, the latter being factory set
and that’s the way it should remain unless the output transistors are replaced.
The installation of the VCE2FS follows normal conventions and should pose no problems.
The VLA2-12 on the other hand has a slightly unfinished feel to it. At the very
least needs some form of mounting bracket or fixing hardware, moreover it
doesn’t look terribly well protected against the ingress of dirt and moisture
and this particular version is really only suitable for indoor installations.
Unfortunately due to various constraints we were unable to conduct any
serious field tests or check the Equalisation Amplifier up to its theoretical
6km limit but there was more than enough cable reels under the test bench to
give both devices a fairly decent workout. The results were impressive. A
simple A/B test, looking at direct and attenuated video signals, with and
without assistance from the VLA2-12 through a decidedly hotchpotch arrangement
amounting to a 300-metre length of coax was most impressive. Unamplified
signals through the cable showed significant levels of noise and a marked
reduction in colour depth but as soon as the launch amplifier was put into the
circuit the image returned to within a whisker of its original condition.
Similarly, feeding an unassisted signal through the VCE2FS equalisation
amplifier, after it has passed through our test cable, bought about an
immediate and very obvious improvement in picture clarity and a worthwhile
reduction in colour noise.
Our admittedly fairly crude tests demonstrate that these two units have
the potential to enable video signals to travel over significant distances with
minimal loss of quality or integrity. Overall build quality is very good,
especially on the equalisations amplifier, which looks virtually bullet-proof,
the launch amplifier on the other hand has a few rough edges and the lack of a
mounting bracket or any guidance in the instructions might lead installers to
suppose it can be safely left laying around, which would be inadvisable.
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