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How to aim long distance WiFi antennas - the low-cost way

Very often I'm being asked how can we aim such long distance WiFi links.

A relatively simple way of doing this would be to use a high-power analog signal transmitter fed into the antenna on one side, with a spectrum analyzer identifying that signal on the other side.

In our global village world - we can find the above for less then $300 (total for both sides), which conventionally would cost way over $10,000:

Buy a high-power 2.4Ghz video transmitter from:www.chinawholesaleonline.org
At first - I was a bit worried to give my credit-card on an unknown Chinese web-site. For once, I'm happy that I was brave enough. The owner of that site - Adam, had dispatched the transmitter immediately, and I got it days later via DHL. However, the unit was faulty, it would often not turn-on, the frequency would not be stable and would shift with temperature and the power was less then 300mW.
For a moment I thought to myself that I deserved it for buying from such an unknown source. However, I have emailed Adam, and he had quickly <"read more", to continue>

 

Chinese video transmitter - 2w

Here is the small transmitter being measured with a spectrum analyzer to establish the power. Look at the nice and stable analog signal which is so easy to spot on the far side.

Wi-Spy modification dispatched a replacement unit (on his expense - including the shipment) this time from another manufacturer. Days later - I was testing the new unit which works flawlessly and emits the expected 2 watts power.

The unit comes with a 4-way switch to select the frequency - all within the WiFi band.

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For the other side - all we need is a low-cost spectrum analyzer - hemm, sound impossible - but there is a solution: buy an extremely overpriced $400 Wi-Spy USB gadget , to replace a full-blown spectrum analyzer. Or buy the half-price and still over-priced older-version WiSpy without the external antenna connector. I opted for the later and decided to modify the unit myself to include the RF connector. The RP-SMA connector cost about $2 and in 10-15 minutes of work I could save the extra $197 - seems like a good deal.

I the photos of the modification should be self explanatory - if anyone have any questions - feel free to use the "comments" below.

I remember someone else who had posted long ago about this modification, but I searched the net and could not find it anymore.

While a bit on the ugly side - it does work well and easy to do. Arguably my selection of PCB-mounted connector was not ideal, but that is what I have in hand at the time. It must also be a bit less lossy then any crimped connector with a coaxial cable - so maybe a bit of increased sensitivity.

Happy aiming...

 

 

 

thank you for the post

Maharaj of all the wifi-walas,

Thank you for the post. This should help solve many of the problems that we face when we are establishing new nodes at far of places. Thanks!

Regarding Mesh Nodes

Hi Yahel,

Sorry to include out of context post.
My name is Pradeep.We are currently working in Indian institute of Madas on finding a reliable and low cost wireless mesh solution to solve the last mile problem for rural india.
We started the project in July end.
By now we have done quite a few tests on coverage and throughput using a $49 meraki mini(802.11g).
Though the coverage was good it failed on throughput as the max throughput we got was around 8 Mbps max.
Right now we are looking to design a reliable outdoor mesh node which would give us a throughput of around 20 mbps at least and for the same we are planning to use a directional antenna to create backhaul link.I have some specific queries.Your input will be valuable
1. What is the structure of your Mesh nodes??
a. Are they single radio or dual radio??
b. Which card you are using??
c. What is the Tx Power and the range ??
d.what protocol you are using..is it WiLD??i have gone through the paper on WiLD.It improves the throughput of links on the range of Kms..but our initial set up we are planning for a max distance between nodes around max 1km.So,can you suggest what protocol to be used??
e. What is the exact list of hardware requirements for building Airjaldi Mesh router??
f. What throughput does the mesh provide on 2,3 hops respectively??
g. How many users a typical air jaldi mesh router supports??
h. whats the cost of the Czech router??
May be i am asking lot of questions .But I have gone through the documentation on Airjaldi provided on the site.But i could not get clear answers of above questions from them. May be you have already answered above questions many times..If you could guide me on this it would be of great help.

Thanks and regards,
Pradeep
pradeep.ghimirey@gmail.com

Thanks!

Yahel, we continue to appreciate your efforts--not just what you're doing for your part of India, but for the rest of the world by documenting your research and discoveries. :-)

I splurged and bought the $400 Wi-Spy. It has better resolution than the $200 model, and I'm also nervous about loosing sensitivity by doing a bad soldering job.

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