Ethernet Radio Modems (5GHz) FAQs

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 available 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.

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. 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 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 dependent 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 can be collected at the repeater and transmitted down to the control centre.

Yes, the modems are provided with several levels of encryption for security (see the programming section of the manual). The highest level available is 152bit AES, which we usually set as the default. You can obviously add your own encryption code.

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.

The maximum recommended distance is 100 metres for CAT-5 cable, between any two units.

This distance can be increased by the use of a router. For example, you could run 100mtrs from your equipment to the router, then another 100mtrs from the router to the modem.

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.