ADSL: Last mile, or last foot?

We often hear about the 'last mile' of copper that runs between telephone exchanges and our houses. We also often hear about distance from the exchange and noisy lines playing havoc with ADSL broadband.

Sadly, it would seem that at least some of the time the ADSL signals actually make it all the way to the customer's premises in a usable state, only to fall at the last hurdle: the ADSL micro-filter.

Until recently I've never given micro-filters much thought. They're rather unexciting devices that hang out of the phone socket generally looking untidy, theoretically filtering out those precious ADSL signals. All ADSL modems/routers come with them, and a lot of the time the ADSL signals are good enough that the quality of the filter doesn't matter that much.

Now, I live close to my exchange, and sync at the theoretical maximum of 8128Kbps down and 832Kbps up. So I was quite surprised when I switched from a Linksys router and supplied filter to a Netgear set. The Netgear, usefully, tells me something called an SNR, or Signal to Noise Ratio, and the higher this is the better the ADSL will perform. 12dB is apparently a good number.

After having never had a problem with my ADSL connection, I was somewhat surprised to learn that my downstream SNR was now just 8dB. This level, it would seem, is low enough to cause problems - constant connection drops in my case. Switching back to the micro-filter supplied with the old Linksys removed most of the connection drops, at least all of those occurring while the line was in use, by pushing the downstream SNR up to 8.6dB.

So, I'd just gained (or lost, depending on how you look at it) .6dB due to using a different micro-filter. And that was the difference between a working connection and a very broken one. Aside from the conclusion that Linksys modems are more robust than Netgear ones, the choice of micro-filter, it seemed, was more important than I could have ever imagined.

Experts and reviewers always say that when buying an MP3 player, even an iPod, the first thing you should do is bin the headphones and buy a proper pair. After all, why have a great music player if you're going to plug some crud into it? The same appears to be true for ADSL and micro-filters.

I decided to take things a step further and replace my BT telephone socket flace plate with one featuring an integrated micro-filter, separating the voice and ADSL signals at source. ADSL Nation are known for producing high quality filters, though until now I'd never really seen the point.

I'm very pleased to tell you that with the ADSL Nation face plate installed I've gained a whole extra dB! I'm now on 9.6dB downstream, sometimes as high as 9.8dB, and having no line drops whatsoever, even when the line is idle. Upstream SNR is also up by a whopping 2dB, from 11dB to 13dB and safely in the 'good' range.

Here are some top tips for all ADSL users:

• Buy yourself a good micro-filter to replace the one that came with your router. They cost between £7 and £12 and, it would seem, are worth every penny.
• Connect your router directly to the master socket. This may mean you need a wireless router, as the master socket may not be near your computer.
• If you can plug your router into the master socket, check if it's of a type compatible with an ADSL face plate that already contains a micro-filter. Then you can filter the ADSL signals at source, and, even better, you don't need micro-filters on any extensions running off of the master.

Finally, BT have a product out at the moment called the iPlate that is being hailed as a miracle cure for ADSL problems. The iPlate doesn't have an integrated micro-filter, you still need a separate one, but is supposed to significantly improve noisy phone lines and thus improve ADSL performance and SNR. Now, from what I've read, the iPlate is particularly aimed at those with complex or poor internal wiring running out from the master socket... so I don't think it's the "fix all" that it's being hailed as, but it's another option.

So go, get out there and improve your broadband. Stop listening to the Internet through a pair of bundled headphones.