RONJA

RONJA (Reasonable Optical Near Joint Access) is a free-space optical communication system originating in the Czech Republic, developed by Karel Kulhavý of Twibright Labs and released in 2001. It transmits data wirelessly using beams of light. Ronja can be used to create a 10 Mbit/s full duplex Ethernet point-to-point link. It has been estimated that 1000 to 2000 links have been built worldwide RONJA (Reasonable Optical Near Joint Access) is a free-space optical communication system originating in the Czech Republic, developed by Karel Kulhavý of Twibright Labs and released in 2001. It transmits data wirelessly using beams of light. Ronja can be used to create a 10 Mbit/s full duplex Ethernet point-to-point link. It has been estimated that 1000 to 2000 links have been built worldwide The range of the basic configuration is 1.4 km (0.87 mi). The device consists of a receiver and transmitter pipe (optical head) mounted on a sturdy adjustable holder. Two coaxial cables are used to connect the rooftop installation with a protocol translator installed in the house near a computer or switch. The range can be extended to 1.9 km (1.2 mi) by doubling or tripling the transmitter pipe. Building instructions, blueprints, and schematics are published under the GNU Free Documentation Licence. Only free software tools are used in the development. The author calls this level of freedom 'User Controlled Technology'. Ronja is a project of Twibright Labs. The building instructions are written with an inexperienced builder in mind. Basic operations like drilling, soldering etc., are explained. Several techniques – drilling templates, detailed checks after soldering, testing procedures – are employed to minimize errors at critical places and help to speed up work. Printed circuit boards are downloadable ready for manufacture, with instructions for the fabhouse. People with no previous experience with building electronics have reported on the mailing list that the device ran on the first try. 154 installations worldwide have been registered into a gallery with technical data and pictures. With the brightest variant of Lumileds HPWT-BD00-F4000 LED and 130 mm diameter cheap Chinese magnifying glass lenses, the range is 1.4 km. The less bright, but easier to buy E4000 variant of HPWT-BD00 yields 1.3 km. The speed is always 10 Mbit/s full duplex regardless of the distance. By definition, clear visibility between the transmitter and receiver is essential. If the beam is obscured in any way, the link will stop working. Typically, problems may occur during conditions of snow or dense fog. One device weighs 15.5 kg and requires 70 hours of building time. It requires an ability to set full duplex manually on the network card or switch to take advantage of full duplex, since it doesn't support autonegotiation. Must be plugged directly into PC or switch using the integral 1 m Ethernet cable. A complete RONJA system is made up of 2 transceivers: 2 optical transmitters and 2 optical receivers. They are assembled individually or as a combination. The complete system layout is shown in the block diagram. The usual approach in FSO (Free Space Optics) preamplifiers is to employ a transimpedance amplifier. A transimpedance amplifier is a very sensitive broadband high-speed device featuring a feedback loop. This fact means the layout is plagued with stability problems and special compensation of PIN diode capacitance must be performed, therefore this doesn't allow selection of a wide range of cheap PIN photodiodes with varying capacitances.