Portishead
England · TV
Position 51.484040, -2.780786 Grid reference ST45887641 Nation England Ground height 85 m Antenna height 25 m Aerial group Group A — C21–37, the low end of the band Polarisation Vertical BBC region West ITV region West ITV news region West Parent transmitter Mendip Ofcom site number 11045 The position is our conversion of Ofcom's grid reference ST45887641 from OSGB36 to WGS84 [V] . Ofcom publish no latitude and longitude for television sites. The transform is verified rather than assumed: on the 3,403 radio records that carry both, it reproduces Ofcom's own coordinates to within 0.1 m.
How far it reaches The share of the UK's 238,895 Census Output Areas where this mast is the strongest signal of its kind. Not the share it reaches at all — most places can receive several transmitters, and only one of them can be the best.
This is a share of areas, deliberately, and not a number of homes. Checked against Ofcom's own published coverage, this model gets the ranking of transmitters right (Spearman 0.861) and over-states how far each one gets by a median factor of 2.5. A share is a ranking statement and survives that; a household count would not, so there isn't one. How this is worked out .
On the map
Where Portishead is the strongest signal for television.
Television This site carries the three public-service multiplexes and none of the three commercial ones, which is the normal arrangement at a relay — 1,059 of 1,169 sites are like this. Channels on SDN, ARQ A and ARQ B are simply not transmitted here, and no aerial will recover them; they need a main station. PSB3 (BBC B) is the UK's only DVB-T2 multiplex and carries every HD channel. Losing the HD channels while keeping the rest is therefore a single-multiplex fault rather than an aerial problem.
Transmitter data is Ofcom's; every dataset and the terms it is used under are listed under sources . Coverage figures are modelled, not measured, and are systematically optimistic .