Where an extender belongs in a building

Roughly halfway between the router and the area to be covered, at a point where the router’s signal is still strong, with as little masonry and metal in the way as the building allows. Not in the dead spot itself. The link-quality light on the unit reports whether a given socket meets the condition, and it is the only reliable instrument for the job.

An extender is a repeater, not a source. The best it can offer the far room is the signal it hears from the router, minus the cost of relaying it, which on a single-radio unit is about half. If the router’s signal at the extender’s socket is strong, half of strong is still useful. If it is poor, half of poor is nothing much, and it will be delivered at the slow, error-tolerant rate that a poor link forces on both hops.

People naturally plug the unit in where the problem is, in the far bedroom or the garden office. That is the one place it cannot work well, because the reason those rooms have a problem is that the router’s signal has already faded by the time it arrives. The extender needs to be placed before the fade, not after it.

Halfway is a starting point rather than a rule. The aim is the point along the path from router to far room at which the signal is still strong enough to relay well, and no further. Sometimes that is a third of the way, because a thick wall stands just beyond; sometimes it is two thirds, because the path is open. The path is what matters, and it is rarely a straight line. A signal that has to pass through two internal walls and a floor to reach a socket on the direct line may reach a socket further along the corridor more easily, because the corridor offers a clearer route.

What actually blocks a wireless signal sets out which materials cost the most, and the answer is not always the thickest-looking wall.

Almost every extender carries a light that reports the strength of the signal it receives from the router. On some it is a colour, on some a row of bars, on some an arrow per band. Whatever its form, it answers the only question placement asks: is the router’s signal strong at this socket? A good reading means the socket qualifies; a poor reading means it is too far along, or the wrong side of something solid.

The reading belongs to the socket, not to the room. Two sockets on opposite walls of the same landing can read differently, because one has a stud wall between it and the router and the other has a doorway. What the indicator lights report describes this light and its relatives.

A wall-plug extender goes where a socket is, which limits the choice. Within that limit, a few things consistently matter.

• Height and openness. A socket at waist height in a corridor generally serves better than one at skirting level behind a sofa. Furniture, particularly anything with a metal frame or a large body of water such as an aquarium, sits between the unit and the router as surely as a wall does.
• Distance from large metal objects. A refrigerator, a boiler, a radiator or a filing cabinet immediately beside the unit shadows a large arc of its coverage. Metal reflects the signal rather than absorbing it, so the shadow is deep.
• Distance from interference. A microwave oven in use, a cordless-telephone base and some baby monitors all transmit in the 2.4 GHz band. A socket beside any of them gives the extender a noisy channel to listen on.
• The floor between. A socket directly above or below the router, one floor away, is often a better position than a socket further along the same floor, because a concrete or timber floor is one obstacle where three internal walls are three.

The router is a source and the extender is not, so a small improvement in the router’s position is worth a large one in the extender’s. A router in a cupboard under the stairs, on the floor behind a television, or at the far end of the house from where people sit, is throwing away coverage that no repeater can restore. Where the incoming line allows the router to stand somewhere central, high and open, the extender may not be needed at all, or may be able to stand somewhere far better. When an extender is the wrong answer takes that thought further.