Note: Bench Testing
Wireless equipment is usually very reliable and basically straightforward to install and operate, however it is important to follow the installation guidelines provided.
One of the most important checks, which is ignored by most installers, is to carry out a bench test prior to installation. This is a fairly quick and easy job, but it may save you hours of work in the field. Power up and test the equipment on a bench and connect it to your subscriber equipment, PLC, Camera, PTZ controller, etc. This will test the equipment and also check compatibility with other elements of the system.
It is far easier to check the system on the bench where you can see both transmitter and receiver and you have easy access. Remember, once installed, you may need cherry pickers, ladders etc., and even then access may be difficult. You will also need and engineer at each end with a mobile to carry out most of the checks if there is a problem.
Carry out a bench test, then if you have a problem give our technical support a call. We can usually sort any problem over the phone fairly quickly. Once on-site, it will be more difficult.
All of the equipment manufactured by RDT is designed to be used in the license free bands. It should be noted however, that these bands and maximum allowable transmit power may vary in different countries. If in doubt, check with your local government radio agency.
As an example, we manufacture the RM9600 Radio Modem in different versions covering the UHF band, 400 to 470MHz. In the UK, the license free band is 458.525 to 458.775MHz. In other countries, there is usually a different part of the band available for license free operation.
This varies with the type of equipment being used, so look at the section relevant to your specific model.
As a general rule, coverage distance is governed by the output power of the equipment, but above all, the height of the antennas and the local terrain. Normally, the higher the antenna the better. Most radio signals require a clear line-of-sight for optimum performance (see next question), but they will penetrate obstacles to some degree. The lower frequencies (UHF) generally have better non-line-of-sight performance than the higher (5GHz) frequencies.
Buildings will attenuate the signal, but by how much depends on their construction. Metal clad structures may block the signal completely. Trees are often ignored, but in fact can cause major problems. A reasonable signal strength may be achieved through trees in the winter, but when clad with leaves, the attenuation will be much greater. The attenuation will also be increased when the leaves are wet, and branches moving in the wind, may cause interference.
This is quite a complex issue and by no means straight forward to answer. In simple terms, it obviously means that there are no obstructions between the transmitting and receiving antennas. In practise, objects that are nearby, or even the ground, may cause reflections and multi-path signals that affect reception.
For a full description see the line-of-sight page.
This question is almost impossible to answer as there are so many variables on each site. In addition, equipment working at higher frequencies, such as 5.8GHz behaves differently to those at the lower UHF frequencies.
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 a video image.
Problems can also be caused by nearby buildings and obstructions that may not necessarily be in the direct path. Radio signals can bounce off these buildings and even off the ground, causing a multi-path effect. If these reflected signals reach the receiver they may partially cancel out the direct wanted signal. This is one of the reasons that mounting the antennas high above the ground improves coverage distance.
With some of the systems we manufacture, such as the digital VideoWave, or VersaNet, it is possible to set up a repeater site to get around obstructions.
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.
If you are operating in a license free band, this is a public access band, open to all users with virtually no control. It is possible therefore that there will be other users in your area, which could cause interference. The affect of this however, depends on the equipment being used and your application.
The Radio Modems and VersaNet Wireless Telemetry system use the same UHF radio. These units are multi-channel, so if the current channel is busy, you can select an empty or less used channel. This normally overcomes the problem. In any case, these units employ a Listen Before Transmit protocol, which means they will delay transmission until the channel is clear. Because they use a proprietary coding system, interference will not cause loss of data or corrupt data.
The 1394MHz VideoWave unit is only single channel (only one license free channel is available) so this cannot be changed. The 1394MHz band is however little used, so interference is not generally encountered. The 5.8GHz units have 6 selectable channels, so a free channel can normally be found.
On these analogue VideoWave units, interference normally shows up as patterns, lines or ghosting on the image. This can sometimes be improved by moving or adjusting the antenna position.
Because of the system employed for the digital VideoWave units, they can co-exist with other users on the same channel. There is of course a limit to the bandwidth available, so again if the channel is very crowded, another channel can be selected.
Interference on digital systems does not affect picture quality, but usually creates a delay caused by missed blocks of data. Any movement in the picture will tend to be jerky, rather than smooth, as blocks of data are lost. This will be particularly noticeable when controlling PTZ cameras, as any delay in the signal will be obvious.
This question is really too general to answer, so you should check more specific topics in the section related to your particular product. There are however a few basic checks that apply to most equipment.
Firstly, check the power supply. The equipment is usually fitted with an ‘ON’ LED to indicate that the unit has powered up correctly. Check this LED (details will be found in the manual or user guide supplied). If there is any suspected problem, check the power supply with a DVM to make sure the correct voltage (usually 12V DC) is connected.
Some units are fitted with signal strength indicators or other LEDs to indicate status (check details in the manual). These should be checked to make sure the unit is behaving correctly and that there is sufficient signal strength. Sometimes it may be necessary to adjust the position or orientation of the antenna.
If everything looks OK, but you are still not receiving a signal, check all the cable connections, especially the antenna connection. If the antenna is mounted externally, make sure that no moisture has penetrated the connector. All external joints should be tightened then sealed with self amalgamating tape during installation.
Make sure the antennas are correctly polarised. If for example the transmit antenna is vertically polarised, then the receive antenna must also be vertically polarised. Wrong polarisation will significantly reduce the signal and in most cases, will probably not work at all.
Finally, the problem may be related to interference from another user on the same channel. There are various means of checking this, but they vary depending on the equipment. See the section on your specific product. If you suspect interference and you have a multi-channel unit, try changing to another channel.
