Freeview TV reception may be affected by 4G interference as UK mobile providers follow EE in launching 4G mobile internet services.
Equipment designed to prevent 4G interference with Freeview TV signal is to be tested at thousands of households in west London.
An organisation called at800 has been set up to assess the extent to which free-to-air TV reception will suffer when 4G mobile internet services, which operate at 800MHz - similar to the frequency used by Freeview - are launched by the likes of O2 and Vodafone.
Now in its third phase of testing, the group is sending specially designed radio filters to 28,000 homes across Bretford and Isleworth, in the London borough of Hounslow.
Simon Beresford-Wylie, chief executive of at800, said: "This test will help us assess any problems viewers may have with fitting filters and whether receiving one in advance improves awareness and understanding of the potential issue.
In the first phase of testing, completed in the West Midlands earlier this month, only 15 of 22,000 homes noticed a problem with their Freeview reception. The second phase is still under way, focusing on 170,000 households in south east London.
At present, the UK's only major 4G provider is the mobile network operator EE, but its 4GEE service operates on a different frequency (1,800MHz) and so cannot cause disruption to Freeview.
In the coming months, O2, Vodafone and Three are all expected to launch 4G mobile internet services using the troublesome 800MHz frequency.
Ofcom, the UK communications regulator, has warned that 4G interference could disrupt the Freeview TV reception of up to 900,000 UK households.
at800 has been funded by the mobile operators, with the sole purpose of helping consumers whose TV signal is affected. For more information, visit the at800 website.