I have a dual band router - top of the line new one - but Wirelesd connection is terrible in basement. I have cable internet. My modem is upstairs and my wireless router. I have a cable outlet in the basement too. How can i get a strong internet source in my basement as well as upstairs? Two routers?
You don't need another router... you only need an access point.
The best way to do this is to buy an access point, and run Ethernet between it and your router. Many access points can also operate in a mode where they relay a wireless signal, but this isn't exactly a reliable or high-performance solution in most cases.
You would need to get a second modem/line to use a second co-axial cable outlet for internet, since cable internet is tied to the modem.
I see two options that may work - power line networking between the upstairs and basement, assuming they're on the same loop, or if possible pulling down ethernet from upstairs to downstairs. You can then plug in a another router or AP as per my answer here