The company says the 'I-Plate' hardware filter, which screws into a phone socket in the home, typically increases broadband speed by 1.5Mbps

BT may have been making a few noises about investing in a fibre-broadband network for the UK — provided it can get a guaranteed return on investment — but it's still banking on getting the most out of Britain's ageing household wiring first.

BT Wholesale has said it will be offering its ISP customers a hardware filter that could potentially improve customers' broadband by filtering out electrical interference in the home caused by TVs, fluorescent lighting and home wiring.

The patent-pending gadget is called the 'I-Plate' and screws into a phone socket in the home. BT said trials of the technology have shown filtered lines can enjoy a variety of improvements, including faster speeds and a more stable connection.

In a benchmark survey of 36,000 lines, BT said filtered lines typically showed a speed hike of up to 1.5Mbps, with some showing improvements of as much as 4Mbps, although BT has warned higher speeds aren't guaranteed.

BT added that the filter can also extend the geographical reach of a broadband service by around 10dB, and claimed households that are some distance from an exchange could see an improved service, while others that were previously beyond the reach of a broadband service may now be able to get it.

Ian Fogg, research director at JupiterResearch, told ZDNet.co.uk sister site silicon.com that the move is "a tactical measure" by BT "to make the best of current broadband technology".

He said: "It should give some small improvements, but it's very much BT trying to prolong the life of putting broadband over telephone lines. If BT was being more aggressive with rolling out optical fibre, which gives a big step change in broadband speeds, this announcement would be much less significant."

Fogg added that some ISPs already offer ways for customers to maximise broadband speeds, such as encouraging customers to plug their broadband modem into the master socket rather than into an extension socket, and providing a broadband router with the same chipset as equipment in the customer's local exchange, which Fogg said can also give a slight speed improvement.

Users of the I-Plate will need to have a BT NTE5 master socket and extension wiring in their home. The telco estimated that seven out of 10 UK homes have the affected master socket and home wiring — some nine million households.

BT said broadband interference is caused by an antenna effect produced by the 'bell wire' — a third wire that runs alongside the pair of wires carrying the telephone and fat-pipe signals — which forms part of the extension telephone wiring that runs around most homes.

The more electrical equipment there is in a home, the more potential interference there is to the broadband line. The I-Plate works by isolating the bell wire and filtering out the interference. The device can easily be installed by customers, according to BT, and fits between the front and back plate of the master telephone socket (as pictured below).

BT Wholesale will be offering the I-Plate to its ISP customers, which, according to BT, may or may not choose to pass on the cost of buying the hardware to customers. Some ISPs may choose to make the gadget available to customers for free, a spokeswoman for BT added.

A recent silicon.com reader poll found that UK consumers are making do with broadband speeds of up to 8Mbps at home, while research earlier this year from price-comparison website uSwitch suggested line speeds are still on average 50 percent slower than the headline speeds advertised.

Copyright © 1995-2009 CBS Interactive Limited. All rights reserved
ZDNET is a registered service mark of CBS Interactive Limited. ZDNET Logo is a service mark of CBS Interactive Limited.