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28.04.17 in Everything

How do 4G filters work?

What’s a filter and how does work?

Radio frequencies at 800 megahertz (MHz) are now used for 4G but, up until 2013, these frequencies could carry TV broadcasts. Because of this, 4G at 800 MHz can still be received by TV aerials. When 4G signal strength is much higher than the received TV signal, it can affect TV reception.

Filters are small devices designed to filter out 4G but allow TV signals to reach the tuners in TVs and set-top boxes, such as BT TV, Talk Talk TV, EE TV and YouView. Because the filters block 4G, they prevent interference.

TV is currently broadcast in the UK on frequencies up to 790 MHz. (There are plans to stop using frequencies from 694 MHz to 790 MHz for TV by mid-2020. More can be seen about this 700MHz Clearance, here).

4G signals currently use frequencies from 791 MHz and higher.

A very good 4G filter should not affect any frequencies used for TV, but effectively attenuate (stop) signals just above 790 MHz.

The filters we supply are electronically tuned devices with capacitors and inductors designed to allow most frequencies to pass but reduce those in the unwanted range to very low levels so they won’t cause interference. Typically, our filters reduce unwanted 4G signals to about one-thousandth of their original strength.

Types of filters

All our 4G filters have similar pass-band and stop-band capabilities.

However, in different parts of the country, TV signals are carried on different frequencies.

In areas where the very highest frequencies (782 to 790 MHz) are not used for TV, filters don’t need a sharp a cut-off between TV and 4G. We call these ‘channel 59 filters’, because they allow TV on UHF channel 59 (774 to 782 MHz) to pass and then start attenuating higher frequencies until they are fully effective at stopping 4G above 791 MHz.

But in some areas of the country, TV is carried on UHF channel 60 (782 to 790 MHz). Filters used in these areas require a much steeper cut-off as there is a gap of just 1 MHz between TV and 4G. These channel 60 filters are of a higher specification.

In addition to channel 59 and 60 filters, different specifications are required for indoor and outdoor use, for individual properties, and large communal installations.

Outdoor filters are weatherproofed to withstand rain, wind and extreme temperatures. They also have F-type connectors, where aerial cables screw into the filter, which are more robust and weather resistant. They are required where households have masthead amplifiers, where TV signals are boosted as they leave the aerial. Filters must always be fitted before any amplification to prevent 4G signals affecting the amplifier.

Communal filters, as well as always being weatherproofed, have a higher specification still. These reduce 4G to at least one ten-thousandth of their original power, so that they cannot be subsequently boosted by more powerful communal amplifiers. This helps ensure the best possible TV signal is passed from the aerial into the system.

Our consumer indoor filters are small and can be fitted behind the TV. They have commonly recognised standard ‘push-in’ coaxial aerial connectors and a separate short fly lead. They are simple to self-install, robust, and safe to handle.

All of our filters are passive devices, meaning they do not require an external power supply.

Need a filter?

If you have noticed new Freeview interference and need a filter for your TV or if you live in a communally managed property and your landlord needs to fit on to a communal aerial, we can provide both types free of charge.

Please call us on 0808 13 13 800 to review your issues and we can arrange for a filter to be sent to you.

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