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TECSEC CABLE EQUALISATION AND LAUNCH AMPLIFIERS

 

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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 monitor.

 

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 problematic.

 

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 and tidy.

 

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.

 

PERFORMANCE

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.  

 

OVERALL ASSESSMENT

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.

 

PRODUCT ASSESSMENT

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                                                  

 

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ã R. Maybury 2002 0802

 


 

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