It won't work if you replace one of them with 2.4GHz antenna. What are you trying to fulfill? Extend Wi-Fi range? If so, why not buy a repeater or range extender?

Connecting directly to your modem, you can get about 1000mbps and it is stable? Did you check the download speed when downloading a file from the internet?

I am asking you login main router's web interface instead of http://tplinkextender.net? Do you know how to login your main router's web interface? What's the IP address of it? Since you can access...

Did you try to disable UPnP?

It is not a bug. Share the reply got from TP-LINK support team: :) The antennas of TD-W8968 are designed with main antenna and affiliated antenna. The affiliated antenna can barely work without the...

What's the security settings on your router? If you just remove the network profile and reconnect with the password, can you connect successfully? http://www.tp-link.com/en/faq-281.html Try...