How to mute your neighbor's WiFi with your second router?

Question

WiFi

Greetings! Recently, I asked a question about increasing the speed of Waffle. As it turned out, the problem is that my neighbor jams everything. I connected another router and the speed result was also bad. The neighbor's point is unscrewed at full capacity and it is she who also catches throughout the apartment. But the point is that he has an Internet DSL for 8 Mbps, and the point is powerful. And I have FTTP for 100 Mbps. It turns out that he specifically jams me, but he doesn’t give a damn, because his speed is not high anyway and he doesn’t jam much.
Moreover, I have not even determined yet where exactly the signal comes from. Or from the next entrance opposite (10 meters), or in my house from above or below. It’s unlikely from my floor, since my apartment and that of another young neighbor are separated by a hut in which my grandmother and grandfather live, who have no Internet. A signal with full power through the apartment in the middle would not have reached.
Question: how can I make sure that his network is cut off and does not interfere with my broadcast. Or at least the second one. There is another old Wi-Fi DSL router. Maybe organize a jammer out of it?
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Added. I changed all channels, but it does not help. Since the signal is so strong that even on other channels there is an intersection.

Answer 1

Just change the Wi-Fi channel. Surely you have a default sixth one there.