Monthly Archives: May 2013

DIY Directional WiFi Antenna + Tests

IMG_20130528_020617IMG_20130528_195107Yesterday I stumbled over the IKEA Baren Toilet Brush – yes, I do keep an eye on toilet brush holders since nazco and myself are planning a directional WiFi link. The box said 10cm diameter, which is a bit too much according to this heise.de article, however, once I arrived at RaumZeitLabor I was surprised that it is “only” 92mm in diameter – the optimal size.

The setup consisted of a TL-WR741ND on our balcony as well as an external Logilink WiFi adaptor which I used to measure stuff along my 2 hour trip.

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Test Point 1

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The TL-WR741ND sat on our balcony, approx 8m above ground level. It was equipped with the stock stub antenna. All tests were done using an external USB WiFi stick (Logilink, unknown model, rt73usb driver). For all test locations, I did the test with the stock stub antenna and my directional antenna.

I’ve used iperf to measure the throughput (iperf server on the TL-WR741ND, and iperf client on my notebook). I could have done send/receive stats, but at first I thought that it wouldn’t work so well if I had only one directional antenna – I was wrong! Performance was much better than expected, even at over half a kilometer I had nearly the same performance using only one directional antenna as I had when I was at home).

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Test Point 3

Big Win: With only one directional antenna, I was able to achieve 18.3 Mbit/s over half a kilometer with a non-optimal line of sight, which is only 4 Mbit/s less than placing both antennas next to each other.

You can find my measurements in the following file: Messwerte.ods (20kb or so)

Additionally, I have visualized the test points on Google Maps.

Note that performance is sometimes less because of trees in the line of sight, and the antenna isn’t constructed in an optimal way. Additionally, my hand is a bit shaky, so there’s room for some additional percent of performance.

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Test Point 4

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Test Point 6

Autonomous WLAN Router Experiment: Part 3 – Up and Running

After hacking the software for the CurrentMonitor, I finalized the case as well as the wiring. I’ve built a frame which holds the solar cell at 33°. I might need to move the cell to get the best performance, but I already got 300mA out of it when the sky was cloudy. I’m curious which performance I’ll get on a sunny day.

I also held a talk at RaumZeitLabor (Slides) and I implemented a cosm feed to publish all data of the cell. If you have questions, contact me.

Solar Powered Router CaseSolar Powered Router: Panel

 

 

Autonomous WLAN Router Experiment: Part 2

I’ve bought some hardware in order to build up the experiment:

  • One monocrystalline 20Wp solar cell (25€)
  • A solar charge controller (15€)

I’ve also built a current/voltage monitoring board, which allows monitoring of the power generated by the solar cell as well as power drawn by the peripherials. Because it also monitors voltage, we can make assumptions of the battery charge status. It uses two INA138 current shunt monitors, together with two 0.1Ω 0.5W 1% precision shunt resistors and a ATMEGA168 (no low power, that’s the one I got at hand). The power monitoring circuit draws less than 10mA at 5V. I have to measure the exact power consumption,   I only recall that the bench PSU was showing 0.00A and my Fluke 27 did show something like 5mA, but I haven’t written down the exact numbers.

So much cool things and then: kaboom! I accidently connected the step-down converter backwards (12V to the output and the 5V router to the input), which delivered 12V straight to the router, which then refused to work. As I couldn’t find any fuse on the router, I assume it is totally bricked and I’ll most likely go with a Carambola2 board, which also requires only 0.5W power.

In the meanwhile, I’ll use a carambola board which uses 1.5W power, but that should be okay until my Carambola2 board arrives.

The current monitoring board can be found at https://github.com/felicitus/CurrentMonitor