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physics

RONJA

RONJA is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand RONJA rather than just read about it. In short: RONJA (Reasonable Optical Near Joint Access) is a free-space optical communication system developed in the Czech Republic by Karel Kulhavý of Twibright Labs. Released in 2001.

RONJA — main illustration
RONJA — illustration

Key takeaways

  • RONJA belongs to physics; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect RONJA to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of RONJA from memory before moving on to harder problems.

Reference excerpt

RONJA (Reasonable Optical Near Joint Access) is a free-space optical communication system developed in the Czech Republic by Karel Kulhavý of Twibright Labs. 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 1,000 to 2,000 links have been built worldwide. The basic configuration has a range of 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. By increasing the diameter of the lens and transmitter pipe diameter, the range can be extended to 1.9 km (1.2 mi). Building instructions, blueprints, and schematics are published under the GNU Free Documentation License, with development using only free software tools. The author calls this approach "User Controlled Technology", emphasising their view on the importance of open-source and user-driven software and innovation

Manufacture The building instructions are very detailed, guiding the builder along the setup. Basic operations like drilling, soldering etc., are explained, along with all technical terms used. 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 a fabrication house (PCB manufacturer). 154 installations, located in multiple European countries and Brazil in South America have been registered into a gallery with partial descriptions, pictures and extra data.

Range With the brightest variant of Lumileds HPWT-BD00-F4000 LED and 130 mm diameter cheap magnifying glass lenses, the range is 1.4 km (0.87 mi). The dimmer but more affordable E4000 variant of HPWT-BD00 yields 1.3 kilometres (0.81 mi). The speed is always 10 Mbit/s full duplex regardless of the distance.

Models Ronja Tetrapolis: Range of 1.4 km (0.87 mi), red visible light. Connect with 8P8C connector into a network card or switch. Ronja 10M Metropolis: Range of 1.4 km (0.87 mi), red visible light. Connects to Attachment Unit Interface. Ronja Inferno: Range of 1.25 km (0.78 mi), invisible infrared light. Ronja Benchpress: A measurement device for physical measurement of lens/LED combination gain and calculation of range from that Ronja Lopipe: The original (discontinued) design using red visible light and a RS232 interface for a max 115 kbit/s PPP/SLIP link.

Limitations As an FSO system it requires clear visibility between the transmitter and receiver. If the beam is obscured in a way that introduces too much noise or fully obstructs it, the link will stop working. Typically, problems may occur during conditions of snow or dense fog. One device weighs 15.5 kg (34 lb) 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 metre (3 ft 3 in) Ethernet cable.

Technology

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.

Optical receiver – Preamplifier stage

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.

… excerpt ends here. Continue reading the full article.

Illustrations

RONJA: Single high-brightness LED with a cheap loupe lens creates a bright narrow[1] beam that can stream DVD-quality video over neighbourhoods. The red beam is invisible when observed outside of its unobstructed path.
Single high-brightness LED with a cheap loupe lens creates a bright narrow[1] beam that can stream DVD-quality video over neighbourhoods. The red beam is invisible when observed outside of its unobstructed path.
RONJA: Twibright Ronja with 130-millimetre (5.1 in) diameter lenses, operating on a 1,205-metre (1,318 yd) link using visible red light, max. range 1,300 metres (1,400 yd), with HPWT-BD00-E4000 transmitter LED. Installed on a rooftop, with its user posing to the right, in Czech Republic.[2][3]
Twibright Ronja with 130-millimetre (5.1 in) diameter lenses, operating on a 1,205-metre (1,318 yd) link using visible red light, max. range 1,300 metres (1,400 yd), with HPWT-BD00-E4000 transmitter LED. Installed on a rooftop, with its user posing to the right, in Czech Republic.[2][3]
RONJA: Three bolts preloaded with pink rubber blocks facilitate fine adjustment of the optical head direction with a gear ratio 1:300.[1] The bolt on the right side is a part of a rough adjustment mechanism which allows pointing the optical head in needed direction.
Three bolts preloaded with pink rubber blocks facilitate fine adjustment of the optical head direction with a gear ratio 1:300.[1] The bolt on the right side is a part of a rough adjustment mechanism which allows pointing the optical head in needed direction.
RONJA: Artificially enhanced picture of fog interfering with a RONJA beam, compromising the connection by introducing interference
Artificially enhanced picture of fog interfering with a RONJA beam, compromising the connection by introducing interference
RONJA: Block diagram of a full duplex RONJA system.
Block diagram of a full duplex RONJA system.

Worked examples

Example 1 — a first encounter with RONJA

Start with the simplest possible case. Write down what RONJA claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to RONJA before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about RONJA ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of RONJA

In research
RONJA appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses RONJA in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
RONJA is common in secondary-school and first-year university syllabi. It links to neighbouring topics Free software projects, Open hardware electronic devices, Physical layer protocols, so understanding it makes those chapters shorter.
In everyday life
Look for RONJA outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study RONJA in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what RONJA means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain RONJA out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is RONJA in simple terms?

RONJA (Reasonable Optical Near Joint Access) is a free-space optical communication system developed in the Czech Republic by Karel Kulhavý of Twibright Labs. Released in 2001.

Why does RONJA matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study RONJA?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on RONJA.

Tags

  • Free software projects
  • Open hardware electronic devices
  • Physical layer protocols

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