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What the different between WiFi antenna and WIMAX 4G antenna?, I want to boost the signal for my router to 4 km, I found this antenna in local store, but it seems weird there is only 1 leg, not like the normal WiFi antenna, leg for TX and the other to the ground, how can i connect this one to the router?

WIMAX ANTENNA

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    \$\begingroup\$ Do you at least know the model of the antenna? If you do then you could do a search online and look for it's datasheet. \$\endgroup\$ – KillaKem Mar 13 '15 at 11:26
  • \$\begingroup\$ I asked the local store about the dp, or if he have any datasheet, they don't know anything about it, i did not found any antenna for long range here in my country, for that i think i will build one from scratch, he gives me 8 antenna like this, and told me just connect them together, i don't think that's true, and i am sure this one for WIMAX not for wifi \$\endgroup\$ – narzan Mar 13 '15 at 19:29
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Allow me to put some numbers together....

A normal wifi router is probably good for a range of 30 metres but you want to be able to project that range to 4000 metres. OK so far?

Now, the link loss of a radio system is basically contained within the following equation: -

Loss (dB) = 32.45 + 20\$log_{10}\$(f) + 20\$log_{10}\$(d)

Where f is in MHz and d is in kilometres. This equation tells you how many dB of power loss you can expect at a given distance with a given carrier frequency.

Of importance here is the distance part of the equation. At 30 metres this contributes a value of -30 dB whereas at 4000 metres this is a loss of +12 dB.

Simple math tells me that you are looking for an antenna with a gain improvement of 42dB above and beyond the current antenna. Maybe your current antenna is a monopole with a gain of about 2dBi. So now you are wanting an antenna with a gain of about 44dBi.

Firstly - what you have shown in the picture will not have a gain of 44dBi. It might be a gain of 10dBi maximum and this leaves you considerably short of the 4km distance you wanted. Maybe use a yagi antenna: -

enter image description here

A 7 element Yagi antenna has a gain of about 13dBi and increasing the number of elements is producing diminishing results

enter image description here

What about a dish antenna? The gain of a dish is: -

Gain = \$\dfrac{4\pi A}{\lambda^2}e_A\$ (see this link)

  • A is the area of the antenna aperture, that is, the mouth of the parabolic reflector

  • d is the diameter of the parabolic reflector, if it is circular

  • \$\lambda\$ is the wavelength of the radio waves.

  • \$e_A\$ is a dimensionless parameter between 0 and 1 called the aperture efficiency. The aperture efficiency of typical parabolic antennas is 0.55 to 0.70.

If you do the math (and assuming an efficiency of 1) you'll calculate that your antenna will need to be 6m diameter. Hope I did the math right.

But, even if you did manage to project your wifi signal to a 4km distance, what are you going to talk to? A dish antenna with this much gain (in fact any antenna with this much gain) will be extremely directional - is that what you want?

I hope you realize that wifi is two-way comms and anything at 4km needs to have a similarly sized antenna to project their signal back - the power needs to be focussed back to the wifi antenna at 4km distance.

Have you really thought thru what you want?

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    \$\begingroup\$ I think your calculations are OK but are extremely optimistic because they ignore all fading losses (which will most likely add a significant amount of loss). \$\endgroup\$ – KillaKem Mar 13 '15 at 13:40
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    \$\begingroup\$ @KillaKem I totally agree but in reality I was trying to demonstrate to the OP the futility of his aims. Definitely add another 20dB onto the antenna for fade margin should the OP think this is a practical solution!! \$\endgroup\$ – Andy aka Mar 13 '15 at 13:47
  • \$\begingroup\$ wow that's a perfect answer! but yagi antenna will not work for me, i am looking to make free wifi hotspot in my area for students :) , I buy UBNT unifi AP, from the datasheet, TX power can be 4W and have 2 internal omni antenna 20dp, and like what you said the other side must have a good antenna too to send the data back, i am thinking to make 2 antennas, omni, and quad antenna on a satellite dish 2m to receive the data, anyway each antenna will have 2w, is that will work for me, or i will receive allot of noise !? \$\endgroup\$ – narzan Mar 13 '15 at 19:55
  • \$\begingroup\$ omni will be just for 1KM, and quad will be for long distance and to receive the data, so from what you said i need omni antenna with at least 10dp for 1km !? but why the AP have 20dp omni antenna and when i test it it's only 300M ?! \$\endgroup\$ – narzan Mar 13 '15 at 20:38
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    \$\begingroup\$ I'm sorry but I can't really comment on what you bought or what problems or misunderstanding you have with what you bought. If you wish, please produce a diagram showing what you are intending to do and maybe raise a new question. Note also that my answer said that a YAGI will not work and then I went on to propose a dish antenna but, that would need to be 6 metre+ in diameter and, as was pointed out by a commenter, this doesn't take into account fade margin. \$\endgroup\$ – Andy aka Mar 13 '15 at 20:44

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