Monday, May 23, 2005

Byte: 6dB margin

The broken broadband saga concluded today, thanks to the visit of a BT engineer. I did get my money's worth from the £60 call-out charge, because it turns out that our phone line to the flat was absolutely crap. BT measure the notional line length from the exchange to your phone by the signal loss in decibels, and our line was 60dB "long", which equates to about 6 kilometres (no coincidence, about the distance between the flat and the exchange at Bagshot), which used to be about the limit of broadband services. This means that the signal is still good for 1Mb broadband, but it gets pretty marginal if your line isn't 100% solid.

After the BT engineer tested the line at my end, he found out that the loss margin (i.e. how much signal your line can lose before the signal gives out) was only 6dB, which was as bad as the engineer said he had ever seen, which explained why the signal kept dropping out at peak hours. As soon as other people started using the same line from the estate network junction box (those green boxes you see by the side of the road) to the main telephone exchange, the losses went way beyond the 6dB margin I had, and just dropped the line. The only solution, he said, was basically just to replace the entire phone line from the flat to the exchange, because it had become too to hold a decent signal degraded. He replaced the line from the flat to the junction box first, tested it again, and the signal quality still wasn't good enough, so he checked things out at the exchange, and found out that there were two main lines from the exchange in Bagshot to the junction box, and my flat happened to be on the one of the two that was inexplicably about 10dB longer than the other one. The engineer switched me over to the other trunk line, and the loss margin on my phone line shot up to 21dB (out of a theoretical maximum of 25dB).

It's now clocking on for 6pm, and we're two hours further in than I normally get before the line drops on a weeknight, so it seems that the call-out fee was well spent. I can finally get around to reviewing that Asheron's Call 2 expansion now. Keep 'em peeled for first impressions over the next couple of days. Not that I'll be playing it tomorrow night, though, since I'm seeing Revenge of the Sith... I hope it lives up to the Episode III levels in LEGO Star Wars.
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