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4G filter types

at800 provides free filters to viewers. Each indoor filter is smaller than a pack of cards and does not need batteries or a power supply. We have tested each type of at800 filter to ensure it works correctly in the UK.

Different types of filters

Viewers with rooftop aerials will require a separate weatherproof filter. The filter needs to be attached to the mast and connected between the aerial and the TV or between the aerial and any masthead amplifier or outdoor splitter by a professional aerial engineer. Viewers living in blocks of flats will require a separate communal filter. All our outdoor and communal filters are designed and tested for outdoor use where adverse weather conditions can occur. Find out more.

When inserted, filters will attenuate the signal slightly and we have set strict targets for filter manufacturers in order to minimise this ‘insertion loss’. This is important when households in areas with a weak DTT signal need to maintain the maximum available signal.

Weak DTT signals are often addressed by adding an amplifier which is designed to boost available signals. These can be mast head (in-roof or on roof) variants or distribution versions designed to share the available signals between different TV equipment in a home. However, in general, amplifiers can increase interference issues. They cannot distinguish between wanted and unwanted signals including signals that are causing interference, therefore reception issues can be made worse.

Channel 59 or 60 filter?

Freeview services are delivered on different frequencies (commonly referred to as UHF channels) from a network of more than 1,150 UK transmitters . Here is a diagram to explain: Each TV UHF channel is 8MHz in width, and all reside between UHF channel 21 and UHF channel 60. New 4G services at 800 MHz are being introduced in the vacated UHF channels (61-68) which were cleared by the Digital Switchover. The 4G services in this capacity do not use 8 MHz spacing but are 10 MHz wide and rather than being called 4G channels are called 4G blocks. There are three 10 MHz uplink (for handsets) blocks and three 10 MHz downlink blocks.

One 8 MHz TV channel is able to carry a number of digital TV and radio stations (for example BBC One, BBC Two, BBC Three etc.) combined – or multiplexed – together to use the spectrum most efficiently. In order to receive and watch all channels available on Freeview, a property must be served by one of the primary 80 main transmitters carrying at least six multiplexes*.

Transmitters across the UK use different sets of UHF frequency blocks to carry the multiplexes. For example, Crystal Palace in London transmits on channels 22, 23, 25, 26, 28 and 30.
* Some primary transmitters also carry two temporary HD multiplexes that, through operating at lower power, reach fewer homes. Some also carry an extra multiplex providing local TV with restricted reach.

4G-Spectrum-Diagram-v2

If any one of the digital TV multiplexes is transmitted on UHF channel 60 and interference to Freeview can be seen, a channel 60 filter is required. If multiplexes are carried on any UHF channel up to 59 a channel 59 filter is needed. To find out what UHF channels your serving transmitter uses to deliver Freeview, visit the Digital UK website and enter your postcode in the coverage checker.

CE Marking

DTG Testing provide a conformance testing service for manufacturers who have supplied at800 filters. The DTG testing service stipulates that filters must be CE compliant. Each product has its own set of compliance information which can be found here. Under its agreement with at800, DTG Testing issues licences to manufacturers for their products that meet the required specification and related tests.