It's not a standard modem. Fiber lines work with media converters rather than built-in modems, suggesting your setup likely includes a router. Extending WiFi can reduce speed and create problems. Avoid using them when you need high demand. If the converter isn't set to bridge mode, double NAT issues may arise—two layers of NAT and firewalls block direct access. Placing coax near the fiber entry point can cause instability. Consider Moca if you have coax close to your fiber connection; it uses coax as Ethernet for a steadier link. You might even install a 4-port switch with WiFi in another room for better performance. If your router has adjustable antennas, tweak their position. Since they’re omnidirectional, slight angle changes can help. If the router sits directly above where you need coverage, that could be the cause. In my home, a 1300 sq ft house with the router on the second floor gives strong coverage in both indoor and outdoor areas. Another choice is mesh networking, which uses separate radios for main and satellite devices, offering more reliable communication than weak extenders.