Measure before you change anything
Open your router's admin page and find the signal readings. You are looking for RSRP (strength), RSRQ (quality), SINR (cleanliness) and the band currently in use. Write all four down together with the router's current location. Without a baseline you cannot tell whether anything you do next actually helps.
Take the readings at a consistent time of day, because cell congestion changes the picture. Comparing a Sunday morning reading with a Wednesday evening one will mislead you about whether a change worked.
As a rough guide: RSRP better than -85 dBm is strong, -85 to -100 dBm is workable, -100 to -110 dBm is weak, and worse than -110 dBm needs intervention. SINR above 15 dB is good, 5 to 15 dB is fair, and below 5 dB will hold your throughput down no matter how strong the signal reads.
Move the router — the free fix people skip
Position is worth more than almost any purchase. Signal enters a building through openings and weakens dramatically through block and reinforced concrete, so a router on an interior shelf is starting from the worst possible position.
Work through the building with a laptop or phone showing the router status page, pausing at each candidate position for a minute so the readings settle. Try window sills on different faces of the building, upper floors, and any position with a clear line toward where you believe the mast is. Height helps almost always.
Keep the router away from metal surfaces, mirrors, microwave ovens, large appliances and other routers. A metal burglar-proof grille directly in front of a window is a surprisingly effective signal blocker and is worth testing around.
- Test at least four positions before concluding that the building is the problem.
- Upstairs almost always beats downstairs.
- A window facing the mast beats a larger window facing away from it.
- Give each position sixty seconds before reading the numbers.
Technician’s tip
If moving the router improves the signal but the good position is inconvenient, remember that a long Ethernet run to a well-placed access point is cheap. Put the router where the signal is and move the Wi-Fi to where the people are.
Lock the band, or try a different network
If your router lets you lock to a specific band, it can be worth testing. A router will sometimes prefer a high band with more capacity but marginal coverage when a low band would give a far steadier connection indoors. Test each supported band for a few minutes and record the results.
Be careful with band locking as a permanent setting. It stops the network from moving you to a better cell when conditions change, so use it as a diagnostic first and a permanent configuration only when the evidence is clear.
It is also worth borrowing a SIM from a different operator and testing the same positions. Coverage varies street by street, and the cheapest possible fix is sometimes a different SIM rather than any hardware at all.
Add an external antenna
When position and SIM changes have been exhausted, an external antenna is the highest-value hardware upgrade available. Mounted outside and above the roofline, it removes your walls from the radio path entirely and can transform a marginal connection.
Directional antennas such as Yagi and panel types offer more gain but must be aimed at the serving mast. Omnidirectional and cross-polarised panel antennas are more forgiving to install and are the right choice when you are unsure of the mast direction or when you want to keep options open.
Your router must have external antenna connectors to use one. Check the connector type as well — SMA, TS9 and CRC9 are all common and need the right lead or adapter. Keep the coaxial run as short as practical, since every metre of cable gives back some of the gain you paid for.
Know when to stop
There is a point at which further spending on the mobile path stops making sense. If a professionally installed antenna at height still produces poor SINR, the limitation is the network rather than your equipment, and more gain will not create signal that is not there.
At that point the honest options are a different operator, a dual-SIM router that can use whichever network is behaving, or satellite for sites with no viable mobile service at all. A good installer will tell you this rather than selling you a third antenna.