Map of United Kingdom TETRA (Airwave) coverage (downlink) at 400MHz.
TETRA / AIRWAVE
TETRA is a trunked digital radio system used by the emergency services.
It operates in the 400MHz band and is commonly known in the UK by it's service name 'Airwave'.
At 400MHz, a TETRA signal has better penetration and coverage than GSM mobile but lacks bandwidth. TETRA handsets have higher power output than a mobile phone and generally speaking the network has less towers operating at greater ranges due to it having reduced capacity compared with GSM mobile.
Making the layer
Green represents a strong signal up to -60dBm, blue is a weaker signal up to -90dBm. Actual coverage will vary due to environmental and atmospheric variations.
This layer was created from 3466 distinct sites provided by OFCOM with the Python client and API. It required the OFCOM data to be rearranged into the CSV format ready for processing. Resolution was kept low at 600 pixels per degree given the large scale of the layer. Radius for each site was kept at a consistent 30km - clearly this varies by site and ERP but during trials 30-40km was identified as an average range of TETRA towers. An average clutter height of 6 metres was applied across the UK for the sake of time/cost and the power output was standardised to 10Watts due to concerns over data accuracy (see below).
UK national coverage for the downlink is good. Dead spots are present in remote rural areas like National parks and the Highlands but these are common to most RF networks also. Tower density increases proportionally with population density, as does the number of Emergency services subscribers.
The map does not show the uplink from the handset to the tower. This is the weaker link in most scenarios and is harder to model in an efficient manner.
During processing of the OFCOM data we were surprised at the effective radiated power of some of the sites which were offered as dBw. When these were converted to Watts ERP, the power exceeded capabilities of most commercial TETRA equipment (10W) by a factor of 10. As the data was lacking in detail, we replaced the dubious power levels with a more realistic 10 Watts ERP. TETRA power output is a controversial topic and we don't want to fuel the fire with the first map we created which looked positively luminous, especially since the data quality is questionable.