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Tilman Hornig - TXT on Devices - Netgear Nighthawk Routers

Trees with email addresses

That moment we got our OpenWRT router connected to the Internet.

Good blog on creating large scale WIFI networks

Nice reverse engineering. and here

South America, especially Peru for some reason, has a big free WIFI movement. Lots of interesting, cheap and efficient designs are shared on forums. Just google “construir antena omnidireccional ranurada” for this particular tall slot design.

The top image is from ‘Red Libre Paraguay’ (Free Net, Paraguay)

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amazing blog about designing WIFI antennae

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Inside a Dipole WIFI antenna

WiLDNeT

Abstract WiFi-based Long Distance (WiLD) networks with links as long as 50–100 km have the potential to provide connectivity at substantially lower costs than traditional approaches. However, real-world deployments of such networks yield very poor end-to-end performance. First, the current 802.11 MAC protocol has fundamental shortcomings when used over long distances. Second, WiLD networks can exhibit high and variable loss characteristics, thereby severely limiting end-to-end throughput. This paper describes the design, implementation and evaluation of WiLDNet, a system that overcomes these two problems and provides enhanced end-to-end performance in WiLD networks. To address the protocol shortcomings, WiLDNet makes several essential changes to the 802.11 MAC protocol, but continues to exploit standard (low-cost) WiFi network cards. To better handle losses and improve link utilization, WiLDNet uses an adaptive loss-recovery mechanism using FEC and bulk acknowledgments. Based on a real-world deployment, WiLDNet provides a 2–5 fold improvement in TCP/UDP throughput (along with significantly reduced loss rates) in comparison to the best throughput achievable by conventional 802.11.

WiFi-based Long Distance (WiLD) networks [8, 9, 23] are emerging as a low-cost connectivity solution and are increasingly being deployed in developing regions. The primary cost gains arise from the use of low-cost and low-power single-board computers and high-volume low-cost off-the-shelf 802.11 wireless cards using unlicensed spectrum. The nodes are also lightweight and don’t need expensive towers [6]. These networks are very different from the short-range multi-hop urban mesh networks [5]. Unlike mesh networks, which use omnidirectional antennas to cater to short ranges (less than 1–2 km at most), WiLD networks are comprised of point-topoint wireless links that use high-gain directional antennas (e.g. 24 dBi, 8◦ beam-width) with line of sight (LOS) over long distances (10–100 km).

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Since early 2004, the TIER group has been studying how to use wireless networks to bring affordable Internet access to rural communities, especially in developing nations. Our groundbreaking research and development has led to countless field deployments serving deserving communities the world over. These deployments have been performed not only by us and our many partners, but also by activists who have downloaded our free code and used it globally.

JaldiMAC: WiFi has been promoted as an affordable technology that can provide broadband Internet connectivity to poor and sparsely populated regions. A growing number of deployments, some of substantial scale, are making use of WiFi to extend connectivity into rural areas. However, the vast majority of the 3.5 billion people living in rural villages are still unserved. To reach these people, new technology must be developed to make small rural wireless Internet service providers (WISPs) profitable.

We have identified radio towers as the largest expense for WISPs; to reduce or eliminate this barrier to entry, we propose a novel point-to-multipoint deployment topology that takes advantage of “natural towers” such as hills and mountains to provide connectivity even over great distances. We make this design practical with a new TDMA MAC protocol called JaldiMAC that (i) enables and is optimized for point-to-multipoint deployments, (ii) adapts to the asymmetry of Internet traffic, and (iii) provides loose quality of service guarantees for latency sensitive traffic without compromising fairness. To our knowledge, JaldiMAC is the first integrated solution that combines all of these elements.

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This paper describes how shrubs have been used as transmitting and receiving RF antennas. The variations of transmitting and receiving characteristics with moist and dry conditions have been studied extensively. It has been found out that the two sets of observations differ by 5-7dB. Modulated wave transmissions and receptions have been studied as well. The behaviour of such antennas are found similar to capacitive loaded T dipole antennas as the Antenna Factor in both the cases are comparable by around 10 dB. Finally it is found that mobile phone receptions are possible with a good performance.

Published in:

India Conference (INDICON), 2010 Annual IEEE

Date of Conference:17-19 Dec. 2010

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Helical coil coupled to a live tree to provide a radiating antenna - 1970 Patent

The HEMAC comprises in effect an air-cored toroidal coil. Alternately it may be described as a helical antenna with its axis bent into a circular shape or a loop. In addition, it differs from a conventional helical antenna in that its dimensions are all very much smaller than the wavelength of its operating frequency. The present device may function as an antenna for directly radiating energy from a transmitter to free space or directly picking up and applying signals to a receiver, or it may function as a coupler for coupling a transmitter or receiver to a larger radiator. In this latter function the HEMAC has been found to be very effective in coupling a high frequency (HF) radio set to a natural radiator comprising a forest. The I-IEMAC coupler was wrapped around a tree trunk. The applied frequency was such that the space between the forest floor or ground and the overhead foliage comprising the interleaved crowns of the trees was approximately the required dimension to form a sort of waveguide or cavity for directing the energy from the HEMAC through the treetops into the airspace above. The conductivity of the foliage and the earth is of course much less than that of the metals of which conventional waveguides are constructed and hence the forest energized by the HEMAC is more analogous to a leaky" waveguide. The energy which leaks from the treetops is propagated through the air and can be received by remote conventional antennas in the open, or by a similar HEMAC receiving system in a remote forest or jungle. The energy which is directed through the forest may be received by a remote HEMAC system. The forest may be converted to an omnidirectional or directional radiator, depending on the location of the HEMAC therein.

The conductivity of the loops will depend on several factors. Assuming the trees are in bloom, the sap thereof carries moisture and nutrients from the ground 42 via the root systems 31 and trunks to the leaves or foliage comprising the crowns 33. The sap flows in the outer ring of the tree, just under the bark. The inner layers or rings of the trunk are relatively dry and of relatively low conductivity compared to the sap-bearing outer ring. The conductivity of the tree crowns will depend on the density of the foliage and its moisture and sap content. The conductivity of the forest or jungle floor or ground 41 will depend on the moisture content and the character of the soil, for example, dry, sandy soil would be less conductive than moist soil containing decayed organic matter. However, even in sandy soil, the interleaved root systems provide a measure of conductivity. The HEMAC 23 surrounding one of the tree trunks comprises in effect the primary of a transformer, with each of the loops 39, 41, 43 and 45 comprising secondaries, through which RF currents will flow. If the RF (Resonant Frequency) is in the lower part of the high frequency band where the wavelengths are of the order 60-80 meters, the quarter wavelength is l5-20 meters and this figure is equal to the distance between the forest floor 41 and the underside of the tree crowns for many typical forests. This distance is indicated as H in FIG. 6. Thus, this space under the tree crowns can act as a giant resonant cavity or waveguide.

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Multi-band tree antenna patent filed 2008

FIG. 4 illustrates an operational concept of the current probes 14. In the receive mode, an external electric field induces current (I) on the tree 12. The current (I) may be coupled from the tree 12 via the current probe 14 transfer impedance to the input of a receiver or multi-coupler. The current probe 14 may be designed such that the current probe 14 will produce a desired transfer impedance Zt over the frequency range of interest and provide the required out-of-band rejection from a co-located transmit system to protect the receive system from damage or electromagnetic interference (EMI) problems. In this instance, the transfer impedance Zt=Vout/Iin. For transmitting, the primary winding 20 may generate high magnetic fields (H) in the ferrite core 16. This magnetic field (H), which equals I/2πr, where “r” is the radial distance from the center of the tree 12 to the field point, induces current (I) on the tree 12, which then radiates the energy.

Initial placement location of each current probe 14 on the tree 12 may be determined by using the length of a ¼-wavelength monopole antenna over a certain band from the following equation: ¼-wavelength=λ/4=c/4f λ=wavelength (m) c=speed of light (300×106 m/s) f=frequency (Hz) For example, the current probes 14 may be initially arranged on the tree 12 utilizing the total height of the tree 12 with the lowest-frequency current probe 14 positioned near the base of the tree 12. Then, each current probe 14 may be “tuned” by moving the current probe 14 up and down the tree 12 or its various branches until the approximately lowest VSWR is achieved. This process then repeats for the next-higher-frequency current probe 14. After each current probe 14 has been initially placed, the VSWR corresponding to each current probe 14 may be measured again. To compensate for minor impedance coupling interaction between the tree branches and the current probes 14, the positions of all the current probes 14 may be adjusted again, following the above procedure, until satisfactory VSWR performance is achieved for each current probe 14.

FIG. 5 shows a perspective view of one embodiment of the multi-band tree antenna 10. In FIG. 5, the multi-band treeantenna 10 comprises a first current probe 14 1 designed to transmit and receive in the HF range (2-30 MHz), a second current probe 14 2 designed to operate in the VHF range (30-300 MHz), a third current probe 14 3 designed to operate in the UHF range (300-1000 MHz), and a fourth current probe 14 4 designed to operate in the L-band range (1000-2000 MHz). As shown in FIG. 5, the first current probe 14 1 may be coupled to a HF transceiver 36. The second current probe14 2 may be coupled to a VHF transceiver 38. The third current probe 14 3 may be coupled to a UHF transceiver 40. The fourth current probe 14 4 may be coupled to a L-band transceiver 42. In this fashion, the tree 12 behaves as the antenna element and the ground 44 that the tree grows out of functions as the antenna ground.

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Long range WIFI is a thing: https://en.wikipedia.org/wiki/Long-range_Wi-Fi

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getting the wifi happening on the OpenWRT router.

('firstboot’ if you need to wipe clean and start again)

firstboot (for fresh install)vi /etc/config/network config interface 'loopback' option ifname 'lo' option proto 'static' option ipaddr '127.0.0.1' option netmask '255.0.0.0' config interface 'lan' option ifname 'eth0' option type 'bridge' option proto 'static' option ipaddr '192.168.1.1' -> ip address's our tplink option netmask '255.255.255.0' option gateway '192.168.1.254' -> address of the router option dns '192.168..1.1 8.8.8.8' /etc/init.d/network restart

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wifi wavelength = 123mm. so A quarter wavelength would be 30.75mm

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