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RAPIDVISION VIDEO PHONE LINE TRANSMISSION SYSTEMS

 

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WHAT OUR EXPERTS SAY...

Sending a high-quality live colour video image over a conventional telephone line is by any reckoning, a rather neat trick. The basic technology was developed by GPO engineers more than twenty years ago, as part of a research project into video phones. It works on the basis that most of the time there’s comparatively little change in a video image from one frame to the next. Therefore it follows that the amount of information needed to convey an image can be drastically reduced by only updating the parts of the picture that change. Domestic video phones using this principle made a brief appearance in the late 1980s but floundered on the fact that it was pointless owning one, unless you knew someone else with a video phone. At around £200 a throw the market was inevitably very small...

 

The original GPO prototype equipment, capable of sending a jerky low-definition black and white picture, filled several floor-standing racks. Work on video processing and compression microchips has made enormous strides since then and now The Vision Research Company have managed to pack all of the technology needed to send and receive up to 16 high-quality colour video images, plus alarm and telemetry information, over a normal public switched telephone network (PSTN), leased line or ISDN connection, into a pair of 2U standard rack mounting cases.

 

Remote site surveillance has become an increasingly important tool for the security industry, but fixed cable or microwave communications links are often either impractical or prohibitively expensive, depending on the distance between the site and the monitoring station. The Rapidvision system effectively takes distance and cost out of the equation. The camera and the monitor can be tens, hundreds or even thousands of miles apart, the only requirements are for a mains supply and telephone line at both locations.

 

Operating costs can be very low indeed. Continual on-line monitoring via a leased line is possible, though it is likely many end-users will elect to use a PSTN communications link. The remote site will only call the monitoring station when an alarm has been activated. This imposes an additional cost burden on the remote site installation, namely that each camera must have an associated alarm sensor, or be linked to a system, but this is unlikely to be a deterrent as by definition in most cases as there will be few, if any video surveillance alternatives.

 

CONFIGURATION

The Rapidvision system makes use of the latest microchip-based digital video processing and compression techniques. The various components are available in a range of configurations, based on the number and type of cameras. We’ve been looking at two variants, based around the CR16 receiver, used with CT4 and CT16, 4 and 16 channel colour camera transmitters.

 

The CR16 16-channel receiver is the core component in a Rapidvision installation, it can be used with any type of transmitter/camera combination -- colour or mono -- and communicate with multiple sites, each of which has its own unique address code. Front and rear panel layouts are reasonably straightforward. It has a pair of composite video outputs, via BNC sockets. There are three 9-pin D-sub sockets. Com 1 is a RS232 serial port, for hard-wire communications with a transmitter. Com 2 is an internal communications port, for external control functions and diagnostics, Com 3 is for an optional keyboard, used for programming.  A 25-pin D-sub socket is used to connect the receiver to a modem or terminal adaptor. A range of settings, to suit most common makes and models, are programmed into the receiver.

 

The front panel is divided into five areas. On the far left side there are four keys for selecting the stored phone directory and initialising dialling. They are also used in various on-screen menu operations. The second group of keys are picture controls, for selecting definition mode, controlling a thumbnail ‘window’ display (more about that in a moment), plus updating and freezing the display. Next to that are the camera selector buttons, they are numbered 1 to 8 and arranged in two groups (A and B), giving a total of 16 switched inputs. This section also contains keys for quad  or octal display mode, and pre-select, which moves the active camera (on a suitable pant/tilt mount) to a preset position.

 

The fourth section has a set of four position buttons, for controlling pan and tilt; there are two keys for zoom in/out, and four buttons for auxiliary functions, including wiper and  lights, plus two other switched outputs. On the extreme right is the program button, mains on/off switch, and indicators for power-on and on-line.

 

A similar set of camera functions are available on the CT16 transmitter unit (for local control), along with two additional switched auxiliary outputs. The rear panel of the CT16 has a bank of BNC sockets for the camera inputs and monitor output. There are the same set of Com ports and a modem socket as the receiver, plus a second 25-pin D connector, for the alarm inputs.

 

The alternative CT4 transmitter (4 colour camera inputs) is housed in a 1U rack mount case; other than the mains on/off switch there are no front panel controls. Around the back there are two 9-pin D-sub Com ports, and two 25-pin connectors for the modem and alarm inputs.

 

On both units two alarm conditions are possible. An off-line alarm is when the transmitter is not connected to the receiver or under local control. An on-line alarm occurs when the transmitter and receiver are in communication with one another. If a single alarm is triggered when the transmitter is off-line the receiver immediately stores a sequence of four images from the associated camera, (presettable at between 0.5 second and 2.0 second intervals). The transmitter initiates a call to the receiver using the first number in its telephone directory. As soon as the connection has been made it uploads the four stored images in a quad format, to the receiver.

Alternatively the fourth image can be live, though this is really only practical on faster ISDN connections; 30 seconds or more can elapse between the alarm being set off, and the images being received, by which time there’s probably nothing to see. If there are two alarm events, a second set of four images are stored by the transmitter.

 

Full frame images are subsequently downloaded, and these can be scanned in rapid succession on the receiver, to aid movement analysis.  The alarm can be released by pressing the freeze button, the transmitter automatically hangs up five minutes after the images have been successfully transmitted.

 

During an on-line alarm event the display immediately switches to the relevant camera and it remains on the screen for a pre-set period or until the operator presses the freeze button. Alternatively the display remains unchanged and display caption reporting the alarm appears on the screen. To prevent screen burn from fixed images the Rapidvision receiver has a switchable screen saver facility (moving and morphing ‘V’ and ‘R’), that comes on after a few minutes inactivity

 

OPERATION

Installation and initial set-up -- using the factory defaults --  is quick and easy. Our review system was supplied with a  pair of US Robotics Sportster Flash modems. The simplest way to verify the operation of the receiver -- once the power, monitor and modem connections have been carried out -- is to call up the telephone directory display, select Vision Research’s test number and press dial. If all is well the receiver will access the manufacturers on-site test system at their UK headquarters in deepest Havant, Hampshire. At the time of writing this had a total of five cameras operating, comprising a mixture of colour and monochrome models, indoors and outside, on fixed and PTZ  mounts, some with switchable wiper and light functions.

 

After the dial button is pressed the main display confirms that contact has been made and shows the baud rate (4800 to 38400 bps); shortly afterwards the first image appears, usually in just over 30 seconds. Each camera display incorporates a site ident along the bottom of the screen; the camera number, time, date, connection and communication status appear on panels at the top of the screen. Once an image has been formed the speed at which it is being updated appears in the top right hand corner of the screen. Depending on the quality of the line, the refresh rate can be as low as 0.1 seconds.

 

If any camera functions are selected (pan, tilt, zoom etc.) a small monochrome window appears in the middle of the image. This has a much higher refresh rate, resolution is very poor, though it is sufficient to show the change the camera position and zoom setting in near real-time. There is lag, lasting between half a second and two or three seconds, between a PTZ button being pressed and the action showing up on the screen. Some practice is needed, to avoid overshooting the desired position or zoom setting. When all operations have been confirmed it’s time to check out the transmitter. 

 

Camera and alarm connections on the transmitter should pose few problems for most installers. Camera telemetry is carried on the video feed, supported protocols are Videmech, American Dynamics and Pelco. Transmitter set-up can either be carried out locally, or more conveniently, from the receiver, once the system has been checked out. The set-up mode is entered by pressing the program button, this brings up the first screen showing basic configuration and status information. To access further menus a pass-code -- up to 12 characters long -- has to be entered. The next menu has three selections, for receiver and transmitter set-up, and exit. Choices are made with a shifting highlight, controlled from the PTZ keys, and confirmed using the dial button.

 

The receiver programming menu contains almost 20 items, covering everything from pass-code re-programming and setting baud rate, to switching off the screen-saver. There’s an equally comprehensive set of adjustments and pre-sets for the CT16 transmitter, including creating site idents, alarm configuration, setting the time and date and scheduling operations. Once the necessary changes have been made the save changes option dials up the receiver and downloads the revised data. The CT4 transmitter has similar remote set-up functions, though it lacks any local camera controls.

 

The quality of construction on all three units is very high. The all metal cases are made from a mixture of steel and alloy and built to withstand a good deal of punishment. The printed circuit boards are neatly laid out and servicing access is good. The instruction manuals are clearly presented, generally well written and easy to follow. A few more diagrams wouldn’t have gone amiss, though. 

 

PERFORMANCE

The instruction manual goes into considerable detail about the system’s limitations. These are mainly concerned with avoiding too much movement on the screen. This can have a drastic impact on transmission speed as larger quantities of data have to be sent. The advice includes choosing a wide angle lens setting where possible, since movement will take up a proportionally smaller amount of screen area. Stable camera mounts are essential, even slight movement will be regarded by the video processing circuitry as a scene change. Trees, traffic, flags and smoke should also be avoided if possible as they will all slow down the refresh rate unnecessarily. The manual also points out that in low-light conditions most cameras turn up their AGC, which results in a grainy, noisy  picture, that the system will interpret as movement. 

 

On the default ‘low’ definition setting digital processing artefacts or ‘blocking’ is normally clearly visible in the image, colour depth and grey scale are quite limited. Selecting the high definition or ‘HD’ mode yields a dramatic improvement, the overall amount of detail and colour fidelity are most impressive, though the refresh rate is significantly slower. Depending on the camera/lens type and scene lighting conditions, even in the low definition mode there’s sufficient detail for critical identification of things like vehicle type colour and even number plates. Clearly it would be unrealistic to expect the same kind of performance from Rapidvision as a conventional fixed connection CCTV set-up, but in HD mode there’s really not a lot in it! Considering the amount of heavyweight processing taking place, in favourable conditions image quality can be surprisingly good.

 

The delays in PTZ control and the slow refresh rate can pose problems; tracking a subject or vehicle, for example, can be extremely difficult, though it does get easier. The lack of any alarm-triggered VCR control facilities on the receiver could also be a disadvantage in some situations, and it a little surprising that the designers didn’t incorporate more alarm functions on the receiver. Even something as simple as simple warning buzzer would be a step in the right direction.

 

OVERALL ASSESSMENT

Quality considerations aside, the convenience, flexibility, cost savings  and security implications of this kind of remote video surveillance cannot be underestimated. Rapidvision clearly has much to offer. The complex technology operates entirely behind the scenes and it is no more difficult to install, set up and use than a fixed-line multi-camera system, though the need for an associated alarm system is obviously a consideration.

 

The reduction in picture quality and lack of full motion video is something to bear in mind, but against that has to be weighed the fact that this system can provide a viable video observation solution at sites where other forms of surveillance are either impossible or uneconomic.

 

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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Ó R.Maybury 1997 0608

 

 


 

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