Advisory note AN-15Coverage
What a published map really shows, why indoors is different, and the only method that tells you what happens at your own address.
Note AN-15 · four sections · reviewed July 2026 · no prices published
Independent status. fernwick is an independent guidance and information service. We are not a mobile network. We are not affiliated with, endorsed by, appointed by or connected to Three, EE, O2, Vodafone, Sky Mobile, Tesco Mobile or any other provider, and we hold no commercial arrangement with any of them. We do not sell, supply, arrange or broker SIM cards, contracts, handsets or services of any kind, and we take no commission. Everything published here is general information and must not be relied upon in place of the provider's own current terms.
Our position in one lineMaps are computer predictions of outdoor signal. One cheap month at your own address is the only evidence that actually counts.
§1What maps show
A coverage map is a model of predicted outdoor signal, built from terrain, mast positions and transmit power. It is a sound first filter and an unsound conclusion.
A stated percentage of population coverage describes people rather than land, and outdoors rather than indoors. It tells you very little about a particular kitchen.
If any of this is unclear
Telephone the advisory and we will talk it through. There is nothing to buy at any point.
020 3896 5248This line is for guidance and information only. We sell nothing, arrange nothing and act for no provider. If anything on this page is unclear, telephone and we will explain it. §2Why indoors differs
Modern insulation, thick masonry and metallised glazing all block radio. This is physics rather than a fault in the service.
- Wi-Fi Calling is the standard remedy — calls travel over your broadband and building materials stop mattering. Free on every major network, and off by default on many handsets.
- 4G Calling is needed for voice now that 3G has closed everywhere.
- Position matters: one metre toward a window changes reception measurably.
- Repeaters bought independently can interfere with the network. Ask your provider what approved option it offers instead.
§3Congestion is a different problem
Full signal bars with nothing loading is congestion — more handsets than the mast can serve — rather than weak reception. It concentrates at stations, venues and city centres in the early evening, and no handset setting resolves it.
Switching network helps a coverage problem and may do nothing at all for a congestion one, which is why the rush-hour test matters as much as the postcode check.
§4Establishing the truth at your address
Run two checkers, weighting indoor predictions.
Buy one rolling month on the intended masts through the cheapest wholesale brand.
Live on it for an ordinary week, testing the rooms you occupy and your commuting point at rush hour.
Re-run the checks once a year — masts are built and re-farmed constantly, and two estates are currently merging.
Before moving house, check the new postcode before exchange. Signal is far easier to verify than to fix.
Speak to the advisory
Telephone the advisory and we will talk it through. There is nothing to buy at any point.
020 3896 5248This line is for guidance and information only. We sell nothing, arrange nothing and act for no provider. If anything on this page is unclear, telephone and we will explain it. Independent status. fernwick is an independent guidance and information service. We are not a mobile network. We are not affiliated with, endorsed by, appointed by or connected to Three, EE, O2, Vodafone, Sky Mobile, Tesco Mobile or any other provider, and we hold no commercial arrangement with any of them. We do not sell, supply, arrange or broker SIM cards, contracts, handsets or services of any kind, and we take no commission. Everything published here is general information and must not be relied upon in place of the provider's own current terms.