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VIDEO WAVE WIRELESS VIDEO TRANSMISSION SYSTEM

 

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WHAT OUR EXPERTS SAY...

No matter how sophisticated a video surveillance system might be it can only be as effective as its weakest link and in a lot of cases that's the cable connecting a camera to the monitoring and recording equipment.

 

Don't get us wrong, modern high-performance coaxial cable is wonderful stuff with many virtues and in the vast majority of installations it provides a perfectly satisfactory means of conveying video signals from point A to point B.  However, there are also plenty of occasions when point A and point B are simply too far apart for a coaxial (or even fibre-optic) cable. There may be barriers or obstacles that would impede a physical connection or a degree of mobility or portability is required at one or both ends of the system.

 

In such instances a wireless or radio link is the obvious answer but until recently this has been a costly and complex route, suitable only for the most demanding and critical applications, where there is simply no alternative. That has begun to change with the Government deregulation of blocks of frequencies that can be used for a variety of signalling and control purposes. The one in particular that interests us here is known as MPT 1349, which is classified as licence exempt within the UK and allows a maximum ERP (effective radiated power) of up to 500mW.

 

Radio Data Technologies (RDT) have been quick to capitalise on MPT 1394 and developed one of the first wireless video transmission systems to operate on the band, in this case a frequency of 1.394 gigahertz. VideoWave is part of a family of devices based around matched transmitter and receiver modules. The system can send live full-motion video signals (and accompanying audio), reliably up to a distance of 2 kilometres, though in tests the manufacturers claim to have achieved transmission distances (over water) in excess of 20km! The system operates at the maximum allowable output of 500mW with a channel bandwidth of 10MHz. With processing that is sufficient for a colour signal or a monochrome picture with audio. The latter facility requires additional components and has to be requested when ordering, unfortunately this point is not made clear in the instructions.  

 

The system we've been looking at, designated KIT 1394 comprises the VTX1394 transmitter module and the matching VRX1394 receiver unit. Both devices are housed in near identical black extruded alloy housings measuring 150 x 85 x 50mm. On the top panels of both units there is a standard TNC antenna coupler whilst at the other end is a single female BNC connector for video input/output, a DC power connector and a 3.5mm minijack socket for the audio. The only significant external difference is the transmitter module has a single dual-colour LED to indicate power on and a video input, whereas the receiver has a row of six LEDs, coloured green, yellow and red, that show signal strength and power on. Identical external 12-volt DC mains adaptors power both devices.

 

Inside each module there are two PCBs, the standard of construction is very good indeed and extensive use is made of surface mount components and state of the art video processing microchips.

 

VideoWave can be used with a variety of antenna configurations dependent on the type of installation and local reception conditions. Ideally the transmitter  and receiver antennas should be mounted in line of sight of one another, thought this is not strictly necessary at relatively close range and the signal will penetrate most non-metallic solid objects (walls etc.). The units are supplied with simple 1/4-wave whip antennas as standard and these are suitable for line of sight installations up to a distance of 750 metres. There are three antenna options, the first is a plug in 1/2 wave design with a 2dB gain, and this is recommended for distances up to 1 kilometre. In situations where it is necessary to use an external antenna RDT have two specialist models available. The first is a 1/2-wave omnidirectional dipole, also with 2dB gain and suitable for line of sight transmissions up to 1 kilometre. The second antenna is a highly directional Yagi antenna with a 14dB gain; this should be used for transmission distances of up to 2 kilometres.    

 

The system as it stands has certain limitations, the most obvious one being the single channel capability. Since the units utilise the whole of the available 10MHz bandwidth available under MPT1394 it can only carry one video signal, though there is no reason why this couldn't be a multi-camera feed from a multiplexer, with a second multiplexer connected to the receiver. The signal is only lightly processed and that means that there is a significant risk of interference if two RDT systems are used in the same vicinity -- i.e. within at least 2km of one another. That also raises the possibility of signals being picked up by a third party on a suitable receiver, though this would entail some effort and a good deal of technical knowledge to produce a coherent image. RDT are working on ways to encrypt the signal to make it less vulnerable to interference and interception, however at the moment it cannot be considered a secure link and this should be borne in mind if the intention is to carry sensitive material.

 

A range of accessories and add-on modules are available for use with the system, these include weatherproof housings, a self-contained battery-powered receiver with LCD viewing screen (for carrying out site surveys and signal strength assessments) and radio modems. These enable data transmission for telemetry control of motorised pan/tilt camera mounts and RDT also produce a multi-camera system, called ScanWave which is capable of transmitting up to four camera feeds. The signals are sent from separate transmitter units that are sequentially 'polled' by a dedicated control unit. Receivers (and transmitters) are available separately so it is also possible to set up a 'broadcast' system with the signal from one transmitter being received at several locations.    

 

OPERATION

Neither the transmitter nor receiver is weatherproof so, depending on the site conditions, it may be necessary to use an external enclosure or antenna. There are no internal or external adjustments to be concerned about though it is obviously wise to establish a clean radio link prior to fixing the transmitter or receiver modules, if they are to be used with the 1/4 or 1/2 wave antennas. Moreover it is important to site the units or antennas well above any movement, and that includes people and objects. Once a suitable location has been found installation is very straightforward. An adjustable mounting bracket is fitted to the cases; the only real constraints are that the cable for an external antenna should be no longer than 3-metres and both units need to be within easy reach of a mains supply.

 

PERFORMANCE

Our test system was used with a range antennas with the transmitter fed with static and moving video feeds from live cameras, a VCR and a signal generator. Under ideal conditions with the receiver and transmitter sited at line of sight distances of up to 500 metres using the supplied 1/4 wave antennas there was no noticeable degradation of the signal, only a very slight increase noise was detected. Signals from standard colour surveillance cameras with a bandwidth in excess of 350 lines made it through without any loss of resolution.  The system is quite sensitive to reflections and ghosting caused by moving objects and this can result in colour instability, however providing the necessary precautions are taken with regard to location and mounting height this needn't be a problem.    

 

Further tests involving increasing the range and simulating distance by attenuating the transmitter signal produced a small but steady increase in noise and colour instability but the image remained very steady throughout. It is clearly difficult to make too many judgements as far as maximum range is concerned, as much will depend on the environment but from our investigations it appears that distances of up to 2km are almost certainly achievable without too much difficulty.   

 

At no time did we experience any interference though it is important to bear in mind that the frequency band has only recently been opened up for this kind of application and there is no way of knowing how congested it could become in the future.

 

OVERALL ASSESSMENT

VideoWave represents a significant advance in wireless video transmission technology. The main benefits are simplicity of installation, ease of use and it is a cost-effective alternative to rival systems. The downside is that the basic system can only handle one video channel without recourse to multiplexing and there is a question mark over interference. Lack of security is another consideration though that is something RDT are hoping to address. Nevertheless, the advantages far outweigh the limitations and for a single point to point video feed, where cabled links are impossible or impractical, VideoWave could provide the solution.

 

FACTS PANEL

Equipment                              VideoWave KIT1394

Product Group              wireless video transmission system

Application                             all CCTV

Manufacturer             Radio Data Technology Ltd

Available from                RDT

Address                                  10 Taber Place, Critall Road, Witham Essex CM8 3YP

Telephone                               (01376) 501255

Fax                                          (01376) 501312

Trade Price (ex VAT)

CE Mark awarded                      yes

Transmitter frequency            1394 GHz

Transmitter power output            500mW

Channel bandwidth                   10MHz

Operating range               see text

Size in mm                              150 x 85 x 50 (both units)

Housing material                      extruded aluminium

Power supply voltage            10 to 15 volts DC

Max current consumption            600mA

Warranty                               

 

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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R. Maybury 1999 1102

 


 

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