In Windows, how do I avoid connecting to a Wi-Fi network through a specific AP?

Question

In my house, I have a network set up like this:

A wireless router connected to a cable modem, which is connected to the Internet. The wireless router broadcasts the Wi-Fi network NET1. My computer is distant from this router but it's still able to connect to it by a faint signal. Between my computer and the router, there's a wireless repeater, which does nothing but get the messages from and to the router and re-broadcast them. Effectively, it's like there are two Access Points to the same Wi-Fi network. The image below may provide a better explanation:

This all sounds very nice, but in practice the repeater adds a tremendous amount of latency to my connection when I connect through it, and in fact I have a better connection when I turn it off and connect directly to the router, even with faint signal. But I can't leave it off as there are more computers further away from the router that can only connect to the Internet by the repeater's signal.

So to the question: In Windows, how do I avoid connections to a Wireless network by Access Point? One thing that comes to my mind is MAC Address banning or something similar, but I don't know how to do this.

I would also appreciate instructions to Ubuntu (GNOME), but I will understand if it would be more appropriate to create a separate question for it.