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FAQ's for Wireless Video Transmission (Analogue)
Q: I am not getting a picture. What checks can I do?
Check the obvious things first such as wiring connections, power supplies etc. If the power supply is connected to the unit, the ‘ON’ LED should be lit. Check also that the antenna connection is fully tightened and that the antennas are correctly aligned.
Refer to the Operation and Installation Instructions supplied with the units for further information
Note: Do not power the unit without an antenna connected. Always disconnect power to the transmitter before connecting or removing the antenna. Failure to do so may damage the unit.
The following checks depend on which VideoWave model you are using (see the model number label on the side of the unit)
If possible, connect the camera directly to the monitor to check that they are both working correctly before starting the installation.
1394 (1.4GHz)
On the VTX1394 (transmitter) make sure the antenna is fitted, then connect the power. Before connecting the video input from the camera, the LED on the base of the unit (bottom of the black aluminium housing – if the unit is in a IP67 housing you will need to remove the lid) should be RED, indicating power ‘ON’. Now connect the video input from the camera and the LED should change to GREEN. If not, there may be something wrong with the camera or video cabling. If you are certain the camera and cabling are correct, then this indicates a fault with the transmitter.
The VRX1394 (receiver) operation is very similar. When first powered the LED should be RED, but it will change to GREEN when a valid signal is received. This indicates that it is receiving a strong enough signal to operate. You may need to adjust the antenna position and direction to achieve the best signal strength. Connect the output to a monitor, DVR etc.
5800 (5.8GHz)
On the VTX5800 (transmitter) make sure the antenna is fitted, then connect the power. The 7 segment LED should light indicating power ‘ON’. Note that this also indicates the channel currently selected. Then connect the video input from the camera.
Repeat this for the VRX5800 (receiver). Check that the 7 segment display shows the same channel number as the TX unit. Check the signal strength on the row of LEDs in the centre of the board. The more LEDs lit, the stronger the signal. If only the red LEDs are lit, this indicates a very poor signal. You should aim to have a minimum of 1 green LED lit but preferably 2 or all 3.
You may need to adjust the antenna position and direction to achieve the best signal strength. If you suspect interference (reasonable signal strength but poor or distorted picture) try selecting another channel (at both ends TX and RX).
Q: Which antenna should I use?
RDT can supply a selection of antennas for each frequency to suit most applications. The high gain antennas should normally be fitted to the receiver (high gain antennas on the transmitter may exceed the permitted power limits).
Mounting of the antenna is important, generally the higher its mounted the better the performance. The cables can also make a significant difference. It is better to mount the unit high on a pole near the antenna keeping antenna cable lengths as short as possible.
See the installation instructions supplied for more information on antennas and mounting details.
Select the antenna from the table below that best suits the application.
|
Model |
Description |
Gain |
Distance |
|
1.4GHz |
|
|
|
|
ANT0003 |
½ Wave Whip (omni-directional) |
0dB |
750m |
|
ANT2350 |
Patch |
3dB |
1km |
|
ANT2351 |
Panel |
12dB |
1.5km |
|
ANT0005 |
Dipole (omni-directional) |
0dB |
800m |
|
|
|
|
|
|
2.4GHz |
|
|
|
|
ANT2400 |
½ Wave Whip (omni-directional) |
0dB |
400m |
|
ANT2373 |
Patch |
3dB |
500m |
|
ANT2374 |
Panel |
12dB |
800m |
|
ANT0026 |
Corner Reflector |
14dB |
1km |
|
ANT0025 |
Dipole (omni-directional) |
0dB |
500m |
|
|
|
|
|
|
5.8GHz |
|
|
|
|
ANT5803 |
½ Wave Whip (omni-directional) |
3dB |
500m |
|
ANT5805 |
Patch |
5dB |
1km |
|
ANT5808 |
Dipole (omni-directional) |
8dB |
1km |
|
ANT5810 |
Panel |
10dB |
1.4km |
|
ANT5820 |
Panel |
20dB |
3km |
|
|
|
|
|
|
450MHz |
Antennas for telemetry modem |
|
|
|
ANT0006 |
½ Wave Whip (omni-directional) |
0dB |
1km |
|
ANT0008 |
Dipole (omni-directional) |
0dB |
5km |
Note that most of the higher gain antennas are directional: i.e. the TX antenna must be aligned with the RX antenna. The omni-directional antennas transmit evenly in all directions.
Distances quoted for the 2.4GHz equipment assume 10mW output power (UK specification).
Q: What is meant by line-of-sight?
When we refer to a clear line-of-sight for radio signals, this is different to a visual line-of-sight. You may be able to see the transmitting antenna from the receiver site, but this does not necessarily mean a good radio path.
A radio signal transmitted between two antennas will spread out forming an elliptical shape that is widest at the mid distance between the two antennas. The area within this ellipse is known as the Fresnel Zone and any obstructions within this zone will cause an obstruction and interference to the signal path.
Note that this Fresnel Zone is three dimensional and has both height and width. The maximum radius of the beam, at the centre, increases with the distance between the two antennas. As a guide, at 2.4GHz the radius for a particular signal path is:
1km signal path 4 - 5Mtr radius
2km signal path 5 - 6Mtr radius
5km signal path 8 - 9Mtr radius
This means for example, that if the link is 2km long, the antennas must be at least 5 to 6 metres above the ground and above any building or obstruction. There must also be the same 5 to 6 metres clearance to either side.
It should also be remembered that radio signals at 2.4GHz will not normally pass through buildings and they will be severely attenuated by vegetation, such as trees.
Even with a clear line-of-sight (as defined above) the ground, or nearby buildings, can cause reflections. These reflected signals will also arrive at the receiver and can interfere with the direct signal causing a reduction in signal strength or lost data.
Q: How far can I transmit non-line-of-sight?
This question is beyond the scope of this document, since there are so many variables and different site conditions. There are specialist publications that give details of the attenuation of various materials.
As a guide, wireless will always perform best line-of-sight. If the obstruction is metal, such as a metal clad building or even a steel reinforced wall, this will almost certainly block the signal completely. Other building structures will significantly reduce the signal strength by as much as 50% for every wall.
Trees can be a problem since they behave differently throughout the seasons of the year depending on leaf density. They also present more of a barrier when wet and they will affect the signal when moving in the wind, producing shadows and distortion on the image.
As a general rule, aim for a clear line-of-sight. If this is not possible, carry out a site survey to check coverage prior to purchasing the equipment. Contact RDT or your supplier for details of site surveys.
Q: Can RDT supply units in Weatherproof Enclosures?
Yes. All of the model numbers with the suffix ‘SE’ or ‘SED’ are supplied in IP67 weatherproof enclosures. These units have cable glands in the base, which should be tightened after installation. All external connectors should be sealed with self amalgamating tape, especially the antenna connection, when installation is complete.
Example:
VTX1394S Transmitter in aluminium box
VTX1394SE Transmitter in IP67 enclosure
VTX1394SED Transmitter with telemetry in IP67 enclosure
Q: Can the telemetry for PTZ operate over the video transmission?
No, the VideoWave units can only transmit the video signal. To transmit the RS485 telemetry, you will require a radio modem, the RM9600. These are available in a combined IP67 enclosure housing the modem and VideoWave unit. The model numbers have the suffix ‘SED’, where the ‘D’ stands for Data.
Example:
VTX5800SE VideoWave Transmitter only
VTX5800SED VideoWave Transmitter and Radio Modem for telemetry.
Q: Will the system work with any telemetry protocol?
The radio modem can be set using DIP switches to various baud rates, parity and stop bits to match most of the common telemetry protocols. See the user manual supplied with the equipment for more details. If your telemetry system is not covered or you are unsure, contact RDT for assistance.
