What actually blocks a wireless signal

Plasterboard and timber cost a little. Brick, stone and concrete cost a lot. Metal, including the foil backing on modern insulation boards and the metallic coating on energy-saving glass, reflects the signal almost entirely. Water absorbs it, so a hot-water tank, an aquarium or a wall of bookshelves full of paper is a heavier obstacle than it looks. The 5 GHz band loses more through every one of these than 2.4 GHz does.

The first loss needs no obstacle at all. A signal spreads out as it travels, so the share of it that reaches an antenna falls with distance even in an empty field. Doubling the distance in open air costs a set fraction of the signal, and the 5 GHz band, being shorter in wavelength, loses a little more per metre than 2.4 GHz.

The second loss is the building. Every material in the path takes a share, either by absorbing energy as the signal passes through it or by reflecting energy back the way it came. A path through three internal walls loses the sum of three walls’ worth, and a single reflective surface can remove more than all three together.

Exact figures depend on thickness, moisture and construction, and published measurements vary widely. The ranking is more stable than the numbers, and it is the ranking that matters for placement.

Both bands meet the same materials, but the higher one loses more at every encounter. As a rule of thumb, an obstacle that takes a modest share of a 2.4 GHz signal takes a larger share of a 5 GHz one, and the gap widens through dense materials. This is why a 5 GHz network that is fast in the same room can be absent two rooms away while the 2.4 GHz one is still usable there, and why an extender’s link to the router is often stronger on 2.4 GHz even when the router offers both.

The trade is capacity. The 2.4 GHz band is narrower, more crowded, and shared with everything from cordless phones to microwave ovens. It travels further and is slower; 5 GHz is faster and stops sooner. A dual-band extender that can hold its router link on one band while serving devices on the other exists to take the good half of each. Why a repeated signal carries less describes that arrangement.

Blocking removes signal. Interference adds noise, and the effect on a link is similar: the equipment falls back to slower, more robust transmission, and capacity drops. The sources are different, though, and so is the remedy, so they are worth keeping apart.

The commonest sources of interference in a home are other wireless networks on the same channel, which in a block of flats can number in the dozens; microwave ovens, which leak energy across the 2.4 GHz band while running; and older cordless telephones, baby monitors and some wireless cameras, which transmit continuously in the same band. None of these is a wall, and moving an extender a metre does not change them. Changing the channel or the band does, which is a matter for the router’s own documentation.

Older houses with solid brick internal walls, modern ones with foil-faced insulation throughout, and flats with reinforced concrete floors are the buildings in which an extender most often disappoints, because there is no socket where the router’s signal survives in any strength. Those are the buildings where a different approach earns its cost.