Is the coax socket connected to the router?
Can the device be set to bridge mode?
If the answer is yes for both, all you have to do is first connect to the spare device, set it into bridge mode, give it an IP and set the gateway IP as the main router IP currently in use. Set your new WLAN SSID different from the original of course.
Then connect the spare device's WAN port to the coax socket. The device should have one if it can be set to bridge mode.
Hello and thank you in advance in helping me out!
Situation: I live with my family and in a huge duplex house. I have an ARRIS DOCSIS 3.0 Touchstone Residential Gateway - MODEL: DG1670A. My bedroom in the corner of first floor doesn't have good signals (I also assume my siblings use too much bandwidth)
I have a same device ARRIS DG1670A with me and a wall socket for Coax cable to plug it in my room.
Request: Please help me out in turning this spare device into a wifi repeater/extender.
Appreciate all the inputs.
Also, please let me know if you need any further details about my primary or spare device settings

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic