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ADSL Inline and Central Filters

C10 Remote Filter / Central Filter

Broadband (ADSL, DSL, ADSL2 & ADSL2+) generates noise on the phone line which causes problems for anything connected to that line other than the computer modem.

A central filter can be fitted in a way that eliminates the need for any additional filters in the house. Central Filters are installed to eliminate "line noise" ensuring:

  • the fastest possible ADSL / broadband speed within your premises
  • elimination of any problems associated with monitored alarms
  • elimination of ADSL modem drop outs caused by star wiring on the premises.

Why alarm systems require Central Filters

Alarm systems, when wired correctly for monitoring, process the phone line first before it has the opportunity to travel throughout the premises or to you modem.

This is referred to as Mode 3.

The purpose of wiring your alarm system to mode 3 configuration, is to ensure it is able to dial out in the event of a break in, regardless if the phone has been accidently left off the hook or if the phone is forcibly removed.

If the ADSL line is the same line being used in monitoring the alarm system, then a good quality Central Filter / Remote Filter or Network Termination Device must be fitted to the premises ensuring that there is no broadband signal being processed by the alarm.

In short, alarm systems hate ADSL broadband and modems hate alarms.

Failure to do so can result in ADSL modem drop outs, slow speeds, synchronisation problems, phone lines cutting out etc.

The benefit of Central Filters with your existing phone cabling

Line health will be dependent on the existing phone wiring.

Energy is required for ADSL signals to travel along phone lines and turn corners.

Therefore, more phone lines / extensions (Star wiring) or phone points connected to the line will result in a poorer quality line or higher line attenuation.

The same goes for corrosion on the line. Corrosion will increase the resistance resulting in a poorer quality signal.

The best way to ensure the best quality signal is to have one phone point wired to standard or install a good quality Central Filter or Network Termination Device with a DSL line module.

A Central Filter or Network Termination Device will allow the connection of many phone line extensions without interference of the ADSL / broadband signal to the modem.

ADSL Inline Filters

ADC Krone inline ADSL filter

If you do not have a Network Termination Device or Central Filter installed, it is essential that a good quality ADSL inline filter be connected to any devices being used on the phone line other than the modem.

Our experience has shown that no more than 2 ADSL inline filters should be connected to an ADSL line if the maximum performance from your service is required.

If additional extensions or devices are required, then a Network Termination Device (NTD) or Central Filter should be correctly installed by a licensed technician.

An ADSL inline filter must not be connected to an alarm system as this is a band aid solution and will not fix noise on the phone line, slow adsl speeds or modem connection "drop outs".


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