The first live test to help assess the extent to which Freeview TV programmes could be impacted by new 4G mobile services has been completed, with less impact than expected.
In certain circumstances it is possible that new 4G services at 800 MHz could interfere with some existing terrestrial digital TV signals.
It is said 4G services operating in higher frequency bands, such as 1800 MHz and 2.6 GHz, do not have the potential to impact Freeview.
In the 4G test only 15 households out of around 22,000 in a test area comprising Cradley Heath and Rowley Regis in the West Midlands reported problems with TV reception caused by 4G.
Before the test, at800, the customer facing testing organisation used by the mobile industry's Digital Mobile Spectrum Limited (DMSL), had a forecasting model which predicted 120 households would be affected. DMSL is funded by the UK's mobile operators.
The 22,000 homes surrounding the 4G at 800 MHz frequency masts were sent information in advance of the testing asking them to contact at800 directly if they experienced problems with Freeview.
Over 100 calls were logged by at800 from these households. Professional aerial installers, as well as TV signal experts from at800, the BBC and Ofcom, visited locations that reported problems to verify their cause.
All issues that could be attributed to 4G at 800 MHz were in television systems with signal amplifiers, either in communal blocks or domestic installations where the amplifier was attached to the aerial.
A filter that blocks 4G signals at 800 MHz from reaching TV tuners resolved problems seen by viewers when installed between the aerial and amplifier. The filter does not affect the use of mobile phones.
Simon Beresford-Wylie, chief executive of at800, said: "This was a useful, small-scale test. We'll now improve our forecast model and look at the approach we use to tackle the issues we've seen. Further extensive evaluation will occur during April and May as masts are switched on for tests across larger urban areas."
Domestic at800 filters are smaller than a pack of cards and when installed correctly block 4G frequencies at 800 MHz, said at800.New 4G mobile services at 800 MHz and digital TV operate in adjacent parts of the radio spectrum. Equipment that receives television signals, such as aerials, amplifiers and digital tuners, can fail to block 4G at 800 MHz.
This can cause loss of sound, blocky images or loss of some or all Freeview channels as viewers receive it through their aerial. BT Vision, YouView, Talk Talk and Top Up TV also provide Freeview services. Satellite and cable TV services are unlikely to be affected by 4G at 800 MHz.
Despite industry assurances however, Ofcom last year admitted thousands of homes would still see their Freeview signals blacked out by 4G services, as they would not benefit from a filter.