Ofcom gave an update to the DTG’s Spectrum Access Forum (30th January 2018) on the progress of the 700 MHz (DTT UHF channels 49-60) Clearance Programme.
Work so far has been delivered according to schedule with minimal disruption to viewers. February and March 2018 will see major changes implemented including frequency changes to Crystal Palace transmitters, covering Greater London and parts of the home counties with viewer support being provided by Freeview and DMSL.
Ofcom has also carried out coexistence testing to assess any impact from 4G handsets operating in frequencies close to those used by DTT.
It has issued a statement with its analysis and has concluded that the impact will be no greater than that of 800 MHz Clearance Programme and that the vast majority of households will not experience any interference from mobile handsets.
However it was noted that viewers with set-top aerials will be more susceptible to interference than viewers with rooftop aerials.
Filters, fitted between aerials and TVs/set-top boxes were deployed during the 800 MHz Clearance Programme to provide effective interference mitigation from 4G interference.
This same method was cited by Ofcom as a potential solution if viewers were to experience 700 MHz interference.
Currently these products are not available but it is hoped they will become available as the clearance progresses.
A further consideration is DTT aerials as some viewers with grouped aerials (such as group C/D covering UHF channels 48-60) may need to replace their aerials to continue to receive DTT.
Ofcom’s advice is to use Group K (covering UHF channels 21-48 – the remaining DTT channels following 700 MHz clearance) for households that are no longer receiving DTT in channels above 48.
However, these antennas would not cater for reception of DTT multiplexes COM 7 and COM 8 which are being moved to channels 55 and 56 on a national single frequency network (the centre frequency gap between the 4G uplink and downlink frequencies) as part of the clearance project.
These multiplexes carry services such as BBC 4 HD, Channel 4+1 HD, and CBeebies HD but are due to be switched off in 2020 when 4G is deployed in the 700 MHz band.
Households wishing to receive these services following clearance can use a wideband aerial (Group T covering UHF channels 21-60) but then also risk picking up interference from 4G when it is deployed above channel 48.
The 700 MHz Clearance Programme also has an impact on the PMSE industry (programme making and special events), as equipment such as wireless microphones and other production equipment are currently deployed in the 470-790 MHz band on a secondary, shared basis, to DTT.
Ofcom is due to release a statement soon regarding the support scheme for PMSE users having to vacate the 700 MHz and procure new equipment as a result.
The DTG runs a PMSE Implementation Group, chaired by BBC R&D, to support the industry in this transition.
DTG Staff | 08.02.2018