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Ofcom warned of wireless interference

30 November 2006

Spectrum management company JFMG (Joint Frequency Management Group) has warned industry regulator Ofcom that impending bandwidth auctions could disrupt programme-making via wireless links, writes Richard Dean.

The conclusion emerged from an initiative by JFMG to explore how wireless cameras perform in the real world, following repeated complaints that the performance of wireless systems doesn’t match manufacturers’ claims even under current frequency allocations.

Tests revealed that wireless cameras in the 2025 to 2110MHz band suffer interference from 3G mobile phone towers operating immediately above, especially when – as if often the case – a roof-top camera receiver is positioned near high power mobile phone transmitters, leading to a severe reduction in operating range.

According to JFMG managing director, Paul Gill, the worst affected channels are likely to be 2105MHz and to a lesser extent 2095MHz, while in extreme cases the performance on any channels in the band may be impaired if the 3G signals are strong enough to overload the wireless camera receiver.

Gill warns that new users in spectrum immediately below this band, and also above 2290MHz, could cause further problems for programme makers. However, equipment manufacturers didn’t emerge as entirely blameless either.

During three days of laboratory tests at the BBC Training and Development at Wood Norton near Evesham commissioned by JFMG, technicians uncovered crucial weaknesses on wireless kit helpfully lent by UK suppliers.

Problems identified across a range of popular wireless receivers included inadequate protection against another wireless camera in the next channel, extreme vulnerability to interference from 3G masts, susceptibility by downconverters to overload by strong signals, greater vulnerability by some HD systems to interference from an adjacent user than for a similar SD system, and adverse effects from other services in unrelated and widely spaced frequency bands.

For wireless camera transmitters, the tests showed that many higher powered systems spilled over into neighbouring channels by more than the permitted amount, with the risk of interference to other users.

JFMG says it will inform Ofcom’s auction advisers of the potential pitfalls facing programme makers from new users moving in ‘next door’. It also plans to provide detailed test data to manufacturers, particularly for wireless transmitters that don’t appear to meet the required performance standard.

But oddly enough, there doesn’t appear to be a minimum performance requirement for wireless camera receivers. The best advice that JFMG can offer is that users “must ensure that the performance is suitable for the type of deployment that is envisaged.”

For further information, see ‘How Green are today’s Digital Wireless Cameras?’ under News and Topics at the JFMG website.

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