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Freeview-watching Londoners are safe from 4G interference, with trials failing to elicit even a single complaint - thanks to the capital's comprehensive coverage and its use of a Freeview band well clear of invading 4G signals.

The tests were carried out by at800, the body charged with spending £180m in mobile-network cash to mitigate forecast interference which is stubbornly failing to manifest.  A test network around Dudley managed to generate 15 complaints, all swiftly addressed, and ongoing trials in Brighton have knocked out Freeview for a handful of viewers (again swiftly fixed) but predictions that 4G telephony would leave two million homes bereft of TV were, it seems, wide of the mark.

The frequencies sold off early this year, and bought by the mobile operators, include a band at 800MHz previously used for analogue TV and the fear was that dodgy TV signal boosters would amplify the 4G signal and knock out Freeview. But with no information on how many boosters were fitted, or how old they were, the scale of the problem was very hard to quantify: which is why operators were cajoled into stumping up the cash and testing has been proceeding with such caution.

Interference wasn't expected in London as the Freeview signal is strong across the capital and the telly frequencies used there are well clear of the 4G networks.  Significant problems would have been disastrous for the mobile operators, but no problems at all is only an issue for at at800 which needs to justify the small mountain of filters it's already ordered in anticipation of problems.

The answer is to mail them out proactively, which is why 28,000 were sent out to Londoners before the test transmissions began. No one will ever know how many are sitting, unused, on hallway tables - or how many will end up in landfill next year - but the mass mailing lets at800 (and, by extension, the network operators) take credit for solving the problem before it appeared.

Brighton will be a more interesting test: the Freeview signal there is right alongside where Three will be deploying 4G, and the local topography restricts the Freeview signal. A few cases of interference have already popped up, but in general it seems that DVB-T (as used by Freeview) and LTE (as used by 4G) are making for good spectrum neighbours.

As the proverb has it, good fences make good neighbours, but we'll never know if the mailshotted frequency fences actually had much effect in this particular case. ®

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