Wi-Fi design and coverage

A house in the old part of town, stone walls half a metre thick, three apartments on three floors. The provider's router sits on the ground floor and a shop bought extender was added upstairs. Guests on the second floor say the connection keeps dropping, even though the extender shows full signal.

Full signal does not mean the link works. The extender picks up a weak signal through the stone and repeats it on the same channel, so the speed upstairs is less than half of what it is downstairs. On top of that, guest devices cling to the more distant point because nothing nudges them across to the closer one.

First we measure signal and interference room by room, including the neighbours' networks that occupy channels. The measurements decide where access points go and how cable reaches them.

• Access points wired back with cable, not chained wirelessly, wherever a cable can be run
• Only channels 1, 6 and 11 on 2.4 GHz, the ones that do not overlap
• Narrower 20 or 40 MHz channels on 5 GHz when there are several access points, so they do not step on each other
• 802.11k, v and r enabled where the equipment supports it, so a phone moves to the nearer access point by itself
• WPA3 on the business network and a separate guest network that cannot see the till or the printer

Wi-Fi cannot be faster than the line feeding it. If the speed on your internet contract is low, new access points will spread it more evenly but will not increase it. We tell you that after the survey, before any equipment is bought.

Older devices that only support WPA2 or only 2.4 GHz will still work, just more slowly. For them it is sometimes worth keeping a separate network in transition mode rather than dragging the whole network down to the level of the weakest device.