Hello, experts, i have alfa ac1900 wifi adaptor but its not working according to my need, i want to catch wifi network from my neighbour friend to my home but it shows only one signal,as my laptop also can show one signal some times , so what can i do ,should i replace antennas or what ,please suggest me guys
Where does OpenWrt come into play?
I dont understand sir what u r asking
And we don't understand what, and why, you're asking us.
Simple english if you dont understand its your problem not mine
If you had been using it, I probably would have...
You think.you are smarter than everyone here so its your misunderstanding please ....
Does that bother you ?
Since this device is only powered via a usb adapter and has no external dedicated AC/DC adaptor the power you would need to get any sufficient db increase in any aftermarket antenna would be a waste of time and money.
As an example. These would mess up your pad with wired extensions to your removable antennas. Back in the day I use a powered amplifier to a suction cup directional antenna for the 802.11b to bring internet from my uncles to my grandmother. Did it again for bringing internet to a new home construction for my parents from my brother in laws.
I assume the one signal you can pick up is the 2.4G and the one your are trying to get a better handle on is the 5G. That's going to be pricy.
Talk to you good friendly neighbors and see if running a cable is within the borrowing sugar kinda scope, or float a balloon, I hear that's all the rage now. 
You could replace the antenna(s) with a directional antenna, but that would not be legal. As a general suggestion, you should move the adapter HIGHER and CLOSER and minimize OBSTCALES (walls, leaves, etc) between the two points.
Run power and ethernet to the remote location of the router.
Oh i sent to someone's else mistake i replied u,?sorry bro
Ok by the way which antenna can i use
The device you have pictured has 4 removable antennas. Two are for 2.4G radio, and likewise the other 2 are for 5G.
You would have to test this by removing pairs to see the degraded signal db. This is somewhat risky as a radio should not be used without the antennas for very long.
You could snap the casing off and take a macro picture of the layout to see where the antenna leads connect to which radio SoC.
But the bottom line is as @hap said, it may be illegal in your country (In), and/or your device is severely limited to powering any extension.
You are posting on the openwrt forum, how is your issue related to openwrt?
Is this usb wlan device connected to an openwrt device of some kind?
He's an OpenWrt member with a non OpenWrt device seeking advice. Simple.