In reply to:

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Edit: To clarify 'SNR'. It is a ratio between signal level and noise level (both being expressed in db). As it's a ratio, it has no unit.

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Sorry, but this is nonsense. Signal-to-noise ratio is measured in decibels (dB). Signal power levels are measured in watts.

The dB is defined as 10 x log(10) of the ratio P1/P2, where in this case P1 is the signal power and P2 is the noise power. In other words the decibel is a logarithmic unit for specifying a ratio (NOT a power level).

Eric

Actually, SNR can be a straight ratio (with no units, as dividing units into each other, removes the unit), or can be expressed in db.
As you say, SNR (with db unit) is 10 x log(10) of the power ratio, but the power ratio expressed without units, and prior to multiplying by 10log(10), is still valid.
Quite what units you use when comparing power level in dbm (which is a valid measurement BTW - dbm is the ratio of the signal level, compared to 1mW) - Maybe still db (as the true dbm/dbm ratio - before mucking about multiplying by 10log(10) - has no units).

All of us are made to suffer pay up and smile whatever service we get. BT believe we should just accept whatever we may be lucky to receive if almost anything.
Instead of just putting up with all this effort and time we should act like the french for example and deliver the message of the paying punters and take it to the world outside. How long is all the knowledge and the friends who just ask for the service that we should be receiving put up with this.
Its time for all to think of some legitamate action. Its time to take this matter to your politicians and make them deliver some results, it can be done. It should be done.
All we want is what we are paying for. Does this have some support please.

You were correct,
BT will not retrain the line or to put it another way they will not fix a fault on equipment owned by BT that I rent from them. After waiting over 2 weeks for an answer to specific question put to them I have given up and asked them to close my complaint (I know it shouldn