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Plusnet Broadband

 
Filters



To prevent interference between the ADSL signal and  analogue devices such as telephones, fax machines, answering machines, set top boxes, alarms etc, Low Pass filters are required. These filters are designed to block all  frequencies above 4 KHz which is basically the broadband signal and allow all speech frequencies which are below 4KHz to pass through.
 
Broadband FilterBroadband Filter
 
Two of the most common types of micro-filter.
 
When connecting any appliance to a broadband enabled line with your filters fitted correctly, there should be no interference between the broadband and speech circuit.
Filters are only required in sockets where there is an appliance plugged into it. So for instance if you have 4 extension sockets but only two telephones, then you would only require a filter for each of the sockets where the telephone is plugged into it.
Some installations have a special front plate which replaces the bottom half of a British Telecom/Openreach Master Socket (NTE5) called a Service Specific Face-Plate. This face plate has a inbuilt filter and therefore requires no further filters. Any extension wiring connected from this main socket would also be filtered. A draw back to this type of inbuilt filter is that you must connect your modem/router in this socket and you are therefore unable to connect your modem/router in a extension socket. Not always useful if you require your modem/router in a different room.
 
Linebox with a built in ADSL Filter
 
BT/Openreach Master Socket (NTE5) with a Service Specific Face-Plate fitted.
 

Typical faults caused by incorrectly fitted or faulty filters are:

  • No synchronization
  • Adsl signal dropping out randomly
  • Slow speeds
  • Noise
  • No dial tone on telephone
  • Incoming calls receive an engaged tone.

To resolve an issue with filters the first thing to think, has the service worked before and if so what has changed?
If the service has worked before the best method is to systematically unplug telephone devices and filters one at a time to isolate the problem. If this fails, unplug all equipment, filters and extension leads and try your router/modem in the test port of your BT/Openreach main socket.

If the service has never worked, check that your modem/router has a solid ADSL light in the BT/Openreach test port. If your service works in the test port then the problem line within your premises. If you cannot obtain a signal in your test port then co-operation will be needed with your Service Provider.

 
Linebox
 
Linebox demonstrating BT/Openreach test port
 
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