page_title: RONJA
section_title: Optical receiver – Preamplifier stage
hierarchical_section_title: RONJA / Technology / Optical receiver – Preamplifier stage
caption_attribution_description: Map showing where the 153 currently (1 October 2007) installations of en:RONJA are located, based on data found at the official site. This map was created by Nikolaos S. Karastathis (NSK), also known as NerdyNSK on Wikipedia, and is a GFDL-licensed derivative work of the 18 April 2007 version of en:Image:BlankMap-World-v5.png which was made available under the GFDL (1.2 or later) by its original creator/uploader Astrokey44 and contributors Dbachmann, Hoshie, Wiz9999, and Tene.
context_page_description: RONJA 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. The device consists of a receiver and transmitter pipe 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 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.
context_section_description: 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.
  Ronja however uses a feedbackless design where the PIN has a high working electrical resistance (100 kilohms) which together with the total input capacitance (roughly 8 pF, 5 pF PIN and 3 pF input MOSFET cascode) makes the device operate with a passband on a 6 dB/oct slope of low pass formed by PIN working resistance and total input capacitance. The signal is then immediately amplified to remove the danger of contamination by signal noise, and then a compensation of the 6 dB/oct slope is done by derivator element on the programming pins of an NE592 video amplifier. A surprisingly flat characteristic is obtained. If the PIN diode is equipped with 3 kΩ working resistor to operate in flat band mode, the range is reduced to about 30% due to thermal noise from the 3 kΩ resistor.
caption: Map showing the distribution of the 153 registered installations of RONJA as of 1 October 2007.  Based on data found at the official RONJA website
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