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ROUTERS – How to increase speed by altering the BT Exchange “Signal to Noise Ratio”- SNR


Your local BT Exchange operates a default SNR of 6.  This is to give you speed, and stability – the double whammy of great ADSL broadband.

However, you may not need an SNR of 6 – if the lines are stable.  If you can decrease the SNR to 3 and maintain stability you will increase your download speeds.



A killer feature is the ability to easily tweak the target signal-to-noise (SNR) margin to maximise broadband speed by taking back control of lines from overzealous Digital Line Management (DLM) systems in exchanges. As shown on our Broadband SNR Margin Tweak page, adjustment of the target SNR margin can substantially increase downlink speeds.

Target SNR margin adjustment with the 8800NL can significantly improve download speeds for many broadband users, as described in our Broadband SNR Margin Tweak page. No longer are broadband users completely dependent upon exchange Digital Line Management (DLM) systems, which can sometimes increase the target SNR margin to very high levels (substantially reducing download speed).

While many broadband lines can function perfectly adequately with a 3 dB target SNR margin without issue, DLM systems often set the target SNR margin above this figure. For example, the default target SNR margins used by BT and TalkTalk equipment are 6 dB and 9 dB, respectively. Furthermore, DLM equipment at the exchange can potentially increase the target SNR margin to 18 dB. Changing the target SNR margin from 18 dB to 3 dB can more than double download speeds!

As with the new Billion 7800DXL, the target SNR margin adjustment feature is very simple to configure, and is accessed from the  ‘Configuration’ ‘WAN’ ‘SNR’ submenu (as shown below).

SNR Configuration menu on the Billion 7800DXL

The table, below, provides the numbers that need to be entered to obtain different reductions in the target SNR margin. We slowly decreased the target SNR margin until we were happy that we had achieved the highest download speed without making the line unstable.

Once you get used to being able to adjust the target SNR margin, it is very difficult to return to a modem without this facility as you really do feel out of control!



Note the Billion 8800 AXL offers all Gigabit ports and high speed 5 GHZ WIFI – using the rock solid Broadcom chip and AC WIFI.  2.4 GHZ offers normally only 300 MBPS, whereas the AC 5 GHZ spec is 3 times faster, and offers 1200 MBPS and over.


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