Can you give me a simple checklist to confirm if the issue is the router, the antenna, or both?

Here's a practical checklist you can use to tell if the problem is the router, the antenna, or both. Start with the baseline: keep the same SIM, test at the same site/location, and use the same devices so the results are comparable; then compare by swapping components in a controlled way: 1) verify the baseline by checking that the router registers and maintains a data path with the current antenna; 2) swap in a known-good antenna (same cable length and mounting) and retest; if performance improves, the antenna path is likely the limiter; 3) if no improvement, swap in a spare router while keeping the same antenna and SIM; if the spare router fixes it, the original router may be faulty; otherwise the RF path or environment is the issue; 4) inspect cabling for damage, verify connectors and mounting; 5) keep power, temperature and time-of-day constant and document readings with timestamps; 6) compare metrics such as signal strength, registration status and throughput to decide which component is limiting. If you want, share your model, firmware version and current status-page readings and we’ll help interpret.