VideoWave Digital (5.6GHz) FAQs

The number of cameras that can be handled depends on several factors. The system has a theoretical maximum bandwidth of 54Mbps, but this will be reduced over distance.

The system is based on 802.11a wireless LAN technology. This has a bandwidth of 54Mbps, but a large percentage of this is used for networking overhead – management of routing, collisions etc. The bandwidth available for sending data is about 24Mbps.

This maximum bandwidth is only achieved at very short distances. As the link distance increases, and the signal strength reduces, the units reduce bandwidth to improve receiver sensitivity. Over a short link therefore, you may have about 20Mbps for data, but this will drop to around 6Mbps for a long link. Another way to look at this is, if you have 5 or 6 LEDs lit on the signal strength meter, you will have an available bandwidth of about 20Mbps. With only 1 LED lit, this will be down to about 6Mbps.

We programme the Encoders / Decoders to adjust the bandwidth used per camera, dynamically, rather than set a fixed rate. This is generally more efficient and only uses the bandwidth required. If, for example, you have a camera looking at a fixed still subject, such as a car park, then the bandwidth required to transmit that image is only about 200kbps. If a car is moving in the image, this will rise to about 500Mbps. If there is a lot of movement, such as when panning a PTZ camera, where the whole image is moving, this requires about 2.0Mbps.

As you can see from the above, there is a huge variation depending on the subject being viewed, from as little as 200kbps up to 2.0Mbps. Using these figures, you can calculate the number of cameras that can be supported on a single link, baring in mind that these figures are an average and that it is not advisable to completely fill the capacity.

As a guide, a short link (high available bandwidth) could support about 50 cameras (fixed image) or about 8 full PTZ cameras (or high movement content). A long link (low available bandwidth) could support about 12 cameras (fixed image) or 1 or 2 PTZ cameras (high movement content).

Note: It is important that the camera is mounted solidly to a firm structure so there is no movement. If the camera is vibrating or moving in the wind, this will in effect cause the whole picture to move, which will waste bandwidth.

All of the above information refers to a single radio channel. There are up to 11 channels available at 5GHz, so various configurations are possible with multiple receivers and transmitters, enabling large numbers of cameras to be supported. See the system overview for example system block diagrams.

This depends on a number of factors, but mainly the height of the antenna above ground, or above any obstructions and having a completely clear line-of-sight.& Line-of-sight is sometimes misunderstood, so for a detailed explanation see the line-of-sight page. From the information on line-of-sight, you will see that over long distances, the curvature of the earth has an effect and antennas need to be mounted high off the ground.

With a clear line-of-sight as defined above and with the antennas at the correct height, distances of over 30km can be achieved.

This question is very difficult to answer.

For a VideoWave system to work correctly and to obtain best results, you must have a clear line-of-sight. See the answer to Q2 above. If there is no line-of-sight, then it depends on the nature of the obstruction and this may vary from site to site.

As an example, a metal clad building or steel reinforced walls will almost certainly block the signal completely. A standard brick wall will probably drop the signal by at least 50%, but this is dependant on the type of brick, wall thickness and the angle the radio signal strikes the wall. Passing through a building with a number of walls will reduce the signal by a significant amount.

In a built-up area, a fairly good reflected signal may arrive at the receiver, which could give acceptable results. This is OK providing the reflection is constant, from a fixed building and is not likely to change. Also, if the exact path is not known, it could be affected by moving vehicles for example.

Trees are another problem, although they are often discounted by installers. They will affect the signal, but the affect will be variable, depending on density of foliage (from winter to summer) and the attenuation will be worse if the leaves are wet. Trees blowing in the wind can also cause multi-path signals resulting in lost data.

For all of the above situations, we advise carrying out a site survey to test the feasibility before proceeding. Remember though, that trees will develop leaves in the summer and they may grow taller.

The 5GHz band is split into 3 parts, A, B and C. Band A is reserved for low power indoor use and band C requires a license. We therefore use band B from 5500MHz to 5700MHz which gives us 11 channels.

On a large site, it is often possible to re-use channels if the geography of the site allows. For example, channel 1 could be used to the north of a large building and used again to the south. The building would ensure no interference between the two.

This depends on how the repeater operates.

If a single unit is used as a repeater, there are two problems. Firstly, it will be receiving 50% of the time and transmitting 50% of the time, which effectively halves the available bandwidth. Secondly, it will be receiving from one direction and transmitting in a different direction. This means that it must use a dipole, omni-directional antenna, which will significantly reduce coverage distance. A single unit repeater will therefore not greatly increase coverage distance.

For the above reasons, we do not offer a single unit repeater. We construct a repeater using two units, a receiver and transmitter connected back-to-back. This means that each unit can be fitted with a directional antenna. So the answer in this case is yes, it can effectively double the distance.

Generally however, repeaters are used to reach non-line-of-sight locations. For example, if the control centre is in a fairly low building, it might be possible to mount a repeater on a nearby tall building or tower. Transmissions from the cameras can be collected at the repeater and transmitted down to the control centre.

Yes. The system is compatible with most types of telemetry protocol.

If you are using the RDT wireless units with IP cameras, then the question does not apply. The wireless unit has an RJ45 Ethernet connector and it will transmit any data sent to this port. The camera or controller may send video, telemetry, alarms, audio, etc. but this will all be sent via the Ethernet port and will be transmitted.

If you are using analogue cameras, with our H.264 encoders / decoders, then these units offer RS485 telemetry. The encoder/decoder has a composite video input, RS485 for telemetry, 2 x two-way digital alarms and two-way audio. The encoder/decoder can be programmed for baud rate, parity etc. to suit most telemetry protocols.

The digital system is not strictly ‘real time’. The video signal from the camera would require far too much bandwidth to transmit as a composite video signal. We therefore take this analogue signal, digitise it and compress it using H.264 technology. At the receiving end, this data is then decoded and output as an analogue signal.

The encoding and decoding requires a powerful micro processor, but even with high speed processing it takes about 400mS (nearly half a second). You will therefore experience a delay of about half a second on your PTZ control. Obviously, the picture is delayed by the same amount, but this is not apparent at the viewing end. If the PTX control is set fairly fine, then with a little practise, it is easy to control the camera.

Most types of camera can be used.

There are two basic options, you can use IP cameras with the RDT wireless units or you can use conventional analogue cameras with the addition of our encoder/decoder units.

If you use IP cameras, then you will require some form of PC based NVR platform to view and record the images. These are normally available from the camera manufacturer or from specialist third party suppliers.

The advantage of the analogue camera / encoder route, is that conventional CCTV equipment can be used. The system is compatible with any analogue CCTV camera that outputs composite video, 1V p.p. It can also control PTZ dome cameras; see the questions above.

The receiver outputs composite video, so to the user, it is virtually the same as using an analogue system, only the transmission part is digital. The receiver output can be connected to a standard controller, matrix switch, DVR and monitor. This is particularly useful for a mixed system, where some cameras are hard wired, or for updating a system with existing cameras.

Yes all of our equipment is supplied in high quality IP67 weatherproof enclosures.

During installation, particular care should be taken to ensure that all cable entries and external connections are made weatherproof by sealing the glands and adding self amalgamating tape where required. If you have a unit with separate antennas, then make sure that after installation, the antenna connector is completely sealed with self amalgamating tape. If not, over a period of time, water will seep into the connector and the performance will deteriorate.

CAT-5: This is required for the data connections between the various units; encoder to transmitter, receiver to decoder, router to any other unit. Maximum recommended distance is 100 metres cable run between any two units.

Co-axial: Use a good quality 75Ω cable, such as RG59, URM70. This is required to connect the camera to the encoder, BNC connector and from the decoder to the monitor, controller etc. Maximum recommended cable length is 200 metres.

Twisted-pair: This is only required for the RS485 telemetry, where PTZ cameras are used. Recommended maximum length is up to 1.2km.

Yes. The encoder / decoder units are fitted with two volt free digital inputs and two corresponding relay outputs. These can be used to send alarms from the camera back to the controller. Because there are two channels in the other direction, you can also send from the controller to the camera, to switch on a light, or start a recorder for example.

No. The telemetry supported via the encoder / decoder is 2-wire or 4-wire RS485. For co-axial or 20mA current loop, you would need to use converters.

This means that there is a clear, unobstructed path between the transmitting and receiving antennas. Because of the nature of radio signals, this path is not just a simple straight line between the two, like a piece of string. There needs to be clearance for an area around this line. Because this is a complex subject, see the line-of-sight page for full details.

This may be caused by a poor power supply, insufficient current or low voltage.

If you are powering the transmitter via the spare CAT-5 wires and the cable is quite long, there may be an unacceptable volt drop. Using a DVM, with the unit still connected (under load) measure the voltage at the input connector. This should be no lower than 10V DC.

If you are providing your own 12V DC supply, ensure that it is capable of supplying at least 1 amp. Although the units only draw 400mA when running, there may be a higher inrush current on power up.

Check all wiring and make sure connections are tight. When power is applied, the ON LED should light.

This could be due to a number of reasons.

Check that all the equipment is correctly located, referring to the system block diagram supplied. Each unit is labelled on the outside of the box. The units are supplied ready programmed, but this means that Transmitter TX1 will only talk to Receiver RX1. The encoder VIM1 will only communicate with decoder VOM1 etc.

Once you are sure all the units are in the correct position, check the cabling. Make sure all the cables are wired correctly and that all connectors are secure and tightened.

If everything is connected OK, then there are a few trouble shooting checks to make.

Firstly, check the signal strength indicator on the transmitter or receiver. This should be indicating a good signal. If you are bench testing the units, this should show full signal strength, all 6 LEDs lit. In the field you should aim for at least the first two LEDs on. If the signal strength is too low, then the encoder and decoder may not be able to communicate.

If there is no picture, is there a message on the monitor screen?

A message stating ‘video loss’ indicates that the encoder and decoder are communicating, but there is no video input from the camera. Check the co-ax connection and if possible, connect the camera directly to the monitor to check that they are both working.

If the message is ‘trying to connect to IP xxx.xxx.xxx.xxx’, then this indicates that the encoder and decoder are not talking. If the signal strength is OK, then try rebooting the encoder and decoder. You can find more information about booting-up and the sequence of the LEDs in the manual.

If the units still fail to connect, then phone the RDT technical support team. You may need a laptop with a network cable in order to fault find in more detail and re-programme if necessary.

On a digital system this is unusual, because both the telemetry data and video signal are converted to digital and transmitted together. If you are receiving a good video image, then the fault is not with the wireless system. The problem is probably the RS485 connection or compatibility with your controller.

The first thing to check is the twisted pair to ensure the correct polarity. Even if you think it is correct, try changing it over. Do this at both ends so that you have covered all combinations. (Note: some manufacturers seem to label the A and B terminals incorrectly. ‘A’ should be –ve and ‘B’ is +ve)

If you have more than one decoder and you have daisy chained the RS485, you will need to remove the terminating resistors on all but the last decoder in the chain. See the manual for details.

On the encoder, there is a red LED fitted across the RS485 terminals. Check that when the joystick is moved, this LED flashes. This will indicate that RS485 data is being received. If the LED flashes, but you still have no control, it may be a compatibility issue.

If possible, connect the controller directly to the camera to ensure that it works correctly when directly wired without the radio link. If this works OK, then check the settings in the decoder. We normally supply the units ready programmed. You will find the current settings printed on the label on the side of the unit, such as 9600, N, 8, 1. If these settings are not correct for your controller, you will either need to change your controller, or re-programme the decoder. You will need a laptop and network cable. Contact RDT technical support for assistance.