This page is to keep track of the progress I've made putting together a Ronja Tetrapolis. Below was taken from the twibright webpage:

Ronja (Reasonable Optical Near Joint Access) is an User Controlled Technology (like Free Software) project of optical point-to-point data link. The device has 1.4km range and has stable 10Mbps full duplex data rate. Ronja is an optoelectronic device you can mount on your house and connect your PC, home or office network with other networks. Or you can use it as a general purpose wireless link for building any other networking project.
The design is released under the GNU Free Documentation License: you get all the necessary documentation and construction guides free. The material costs are very low, about 100 USD. The operation is immune to interference and quite reliable - interrupted only by dense fog.

Of course I don't follow the directions on the Ronja website 100%. I had to make substitution with materials I was able to find. It should also be noted that so far this project has cost me much more than 100 USD. I am confident that it would be possible to manufacture Ronja's at least below the $200 mark if you knew what you are doing, buy in bulk, and build many of them at once.

I've wrote a paper that goes into more detail about the Ronja. If you are interested you can read it here.


I cheated here. I purchased a pre-assembled slightly modified version of the electronics from FASTO located in the Czech Republic. This included two twisters, two receivers and two transmitters.

I have tested the electronics. I hooked them up to two computers and separating the sender and receiver by half a meter. It successfully created a 10Mbit network over free space.

Optical Heads

The construction of the Optical heads is underway. Below are some images and comments.


These are cut sections of a 6“ duct pipe found at a hardware store. This will house the electronics on the inside. Cutting these sections with a hack saw has been the most labor intensive part so far.

Back Caps Front Caps

These are duct caps that will be the front and back of the Ronja. The back cap will only have a small hole for a cable to go through. The front caps hold the lens and have had a large circle cut in them. The cut out circle also will act as a thermal shield for the electronics later.


These are the hoods that will go at the front of the Ronja to block unwanted light. The hoods are made out of aluminum flashing. You can by the material buy the foot at local hardware stores.

Tube, Cap, and Hood

This is a assembled Tube, Front Cap, and Hood. This gives you an idea of what the final product might look light. These are of course unpainted still.


These are the optics, 5” magnifying glasses that were bought over the internet. The focal length was measured using a red laser with wax paper over the front, shined through the lines projected onto a box as a single point. The distance from the lens to point of focus was measured (l), and the distance from the source (laser) to the lens (l').

focal point f=1/(1/l' + 1/l)


My first attempt at sealing the lens to the cap. It was a failure. There was large holes in the sealant. I tried to do it the way described in the Ronja instruction by putting a layer of silicon sealant on the caps first for the lens to go on top of. This ended up being very problematic as silicon sealant doesn't like to stick to itself. I also think I was using the wrong kind of silicon sealant. If you look on the container it rates how well it sticks to certain substances. The one I was using did not stick to metal as well. I had to remove all the silicon from the glass and metal. I had to scrap it off of the glass with a razer blade. It took quite some time.

Lens and Cap, Second try went much better.

My second attempt went better. I used silicon sealant rated well for metal and glass. I did not put a layer of sealent under the lens. Also to make it more clean I put masking tape on both sides of the lens before applying the sealant.

Thermal Shield, Holder/Focuser Apart Thermal shield, Holder/Focuser Together-Front Thermal shield, Holder/Focuser Together-Back

Holder/Focuser without shield inside Tube Holder/Focuser with sheild inside Tube

The transmitter and reciever will be screwed into the thermal shield (circle metal plate). It will be held inside the tube like shown above (Note these pictures are without the RX and TX units). There are slots cut in the tube that allow you to move it back and forward. Adjusting the nuts on the threaded rod allows for adjustments in X, Y. The fast U nuts connected to the corner bracket, make it possible to screw in the thermal shield without needing access to the front.


The heel will be bolted to the botom of the Head and will be connected to the mount.

Defroster on lens uncovered. Defroster on lens covered

This is a set of resistors in series that provide heat to keep the lens from fogging or getting ice on it.

Painted parts

The weather did cooperated and I was able to paint most of the parts for the optical heads.

I also found out there is silicon sealant that CAN be painted. Normal silicon sealant is unpaintable and anything the sealant once touch becomes practically unpaintable.

Gary let me use his drill press which was able to drill through steel like butter saving me many hours. The steel is used to mount which holds the heads (Pictures to come).

I went to install the Ronja. I found it very hard to align everything and gave up. Next time I will use a finder scope. I will also align it during the night as suggested in the Ronja instructions.

Below is a video showing you the mount, as well as one end of the setup we did today on top of a roof. The other end was going to be near the field goal where I zoom in on.

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Short Range Ronja Test

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Current Activity

  • Get finder scope.
  • Going to a quick distance test with the Ronja, of perhaps 1/4 to 1/2 mile, when the weather is nice and at night.


  • More Testing and Enjoy!

ronja.txt · Last modified: 2010/10/08 01:49 by russ