FAQ Tropical

Freespace optical systems can transmit through glass, however, for each glass surface the light intensity is reduced due to a mixture of absorption and refraction. Accordingly we recommend that the operational distance of a system is reduced by 50% (if you want to achieve a distance of 200 meters through glass you would require a 500 meter system).

2) Can freespace optical systems be used for temporary solution or back up use ?

The unit only 7.5Kg in weight and may be relocated as required. The units are ideal for rapid deployment, in the case major break in an existing cable, or for occasional use.

3) Are any special permits or licenses required ?

One of the many advantages of using freespace optical technologies is rapid installation. Because the system uses low power laser, or high power LED, radio licenses, right of way permits or other approvals are not required.

4) How do freespaces optical systems work ?

Freespace optical systems work basically the same as fiber optic cable expect the beam is transmitted through open space rather than glass. Two parallel beams are used, one for transmission and one for reception, therefore allowing full duplex across the link.

5) Do freespace optic create a safety hazard ?

Our laser systems do not require certification for handling or operation. The small power output used makes the laser harmless if used correctly and are certified eye safe according to the requirements of BSEN60825-1.

6) Can the link be remotely monitored ?

Tropical Series can offer a range of management options for all products in the portfolio. These solutions range from simple dry contact alarm monitors, dial up link monitors, SNMP options through to high level OMC total network management solutions.

7) What happens if a bird flies through the laser beam ?

If a bird (or any other object) should pass through the beam, no harm will be done (To the equipment). However, the data transmission will be momentarily interrupted. Ethernet will retransmit the data as per protocol, multiplexed hierarchical systems will report low level error codes.

8) Are laser systems Infra Red ?

Our laser systems operate in the near Infra red region of the spectrum. The emitted radiation across the link is at a wavelength of between 810 - 920nm.

9) How much maintenance or adjustment is required ?

When installed correctly, Tropical series freespace optical transmission systems require very little maintenance, however, an annual maintenance contract is available to cover for those unforeseen events.

10) How secure is laser-based communication ?

Laser transmission is very secure for several reasons:-

Laser transmission has a narrow optical beam path, any potential eavesdropping will result in an interruption of the data transmission.
The narrow infra red beam is not accessible unless viewing directly into transmitter path.
The existence of laser beams cannot be detected with spectrum analyzers or RF meters.
Various proprietary transmission protocols are used, which provide additional security.

Laser system have been used for many diverse applications requiring confidential communications, including financial, medical and military networking.

11) Can sunlight affect freespace optical systems ?

Due to the equipment operating in the near Infra red spectrum then yes it is possible for them to be affected by strong sunlight. However this would only be possible if the Infra red heads were mounted in such a manner whereby the sun could be directly behind one of the heads, e.g. if equipment was installed in the UK, in an East or West orientation with one head on a low building (one or two storeys high) and the opposing end was on the top of a high building (ten or twelve storeys) then it is theoretically possible for the sun to be directly behind the head twice a year, start and end. The affect this would have would be that the natural IR signal generated by the sun would be received at the lower head and would give the impression of cross talk. The sun, however is only in this positions for a period of about 20 minutes, after this time the heads would restart communications as normal.

As stated this is a theoretical situation. If the units are to be installed in an orientation where it may occur it is easy to install the higher head in a position whereby the sun cannot be directly behind it e.g. on the side of a wall of a roof top plant room instead of the top. In addition for the situation to occur you must also have a clear blue sky.

Another theoretical situation that could cause outage, is scintillation (heat haze). If freespace optical units are mounted in a situation whereby they are operating over an expanse of tarmac, or a surface prone to scintillation, the distance to be achieved is in excess of 500 meters and the height from that surface to the central part of the transmission signal is less than 20 feet than the transmission signal could suffer from an amount of refraction which would be enough to interrupt the signal. Again this is a theoretical situation and one which can be overcome at the time of assessment for an installation.

12) What conditions cause outage of freespace optical systems ?

The effects of weather on the operational performance of freespace optical systems vary with the severity of the weather condition encountered. Specific weather conditions such as rain, snow, fog, mist, etc, can impair visibility and thus reduce the effective range of freespace optical transmission. Such effects are transient, yet common seasonal trends are determined by the climate zone, the latitude and other known geographic parameters of the area where the installation is to be located.Tropical Sries publish effective fade margins for each type of system and can supply a software tool to assist in the availability calculation for differing scenarios using the international weather table as reference.

13) What are the limitations of infra red ?

When assessing the viability of utilizing Infra red technology a number of factors must be addressed:

Is there direct line of sight? As freespace optical systems operate point-to-point they require a clear line of sight. When assessing installations allowances must be made for any trees or obstructions etc, which may impair operation. Typical things to look for are young trees with considerable growth left or areas of land that may have construction work carried out.
Distance to be achieved. Tropical Series has an operational distance of up to 4KM. At this range our infra red equipment is cost effective when compared to microwave or leased lines.

14) What is the MTBF rate of the equipment ?

When using Milstres 217F software, a standard Tropical link has an overall MTBF figure in the region of 105,000 hours. This equates to greater than 11 years.

15) What approvals does the equipment comply with ?

Within the UK an Europe, the equipment carries CE approval:

BS EN 50081/1 for Emissions
BS EN 50082/1 for immunity
The Electrical Equipment (safety) Regulations 1994
The safety of Laser Product Part 1 : Equipment classification, Requirement and user Guide. BS EN 60825-1: 1994.
The telecommunications product covered under the OFTEL approval NS/G/12345/J/100003. This allows the equipments to be connected directly between apparatus covered by BABT approval and which forms the final connection to the telephone network.
Homologation (Polish and Russian).