Freeview TV signal could be disrupted by 4G interference as more UK mobile providers join EE in launching their own 4G data services.
4G interference and its impact on Freeview will be measured in a London trial.
A special group, at800, has been established to assess the extent to which free-to-air TV will suffer when 4G mobile services at 800Mhz - a similar frequency to that used by Freeview - are launched by providers such as O2 and Vodafone this summer.
The tests in London will focus on 170,000 homes likely to be affected in Greenwich, Lewisham, Southwark and Tower Hamlets. Residents will be asked to report any issues.
In the first such trial, completed in the West Midlands last week, only 15 of 22,000 test households noticed a problem with their Freeview reception.
Simon Beresford-Wylie, chief executive of at800, said: "These larger tests are essential to help improve our forecast model and the way we'll tackle potential issues caused by 4G at 800MHz. We're extremely grateful to viewers in south-east London for their help with these tests."
At present, the UK's only major 4G provider is EE, but its network operates on a different radio frequency (1,800MHz) and so won't cause disruption to Freeview.
In the coming months, O2, Vodafone and Three are all expected to launch 4G networks using the troublesome 800Mhz frequency.
Communications regulator Ofcom has warned that 4G interference could knock out the Freeview TV reception of up to 900,000 homes across the UK.
at800 has been funded by mobile providers themselves, with the sole purpose of helping anyone whose Freeview TV signal is disrupted by 4G.
Households affected by 4G interference will be supplied with special filters that should eliminate the problem. For more information, visit the at800 website.