Noise & ADSL Micro-filters

[Dopamine]

Does anyone know how to test ADSL micro-filters for correct operation?

I have a line that for a long time was showing a 2db drop in noise margin each time a phone call was made or received. A few weeks ago all problems with the line stopped, but in the last week they've started again. Strangely, there are times now when phone calls cause an increase in noise margin from 15db to around 17db, but it's also quite common for them to cause a complete resync, usually only at 160kbps if the resync occurs whilst the call is still live.

Unfortunately, the problems don't happen with every phone call, and don't appear unique to any one of several micro-filters that have been tried.

Normal line stats are 60db downstream attenuation, syncs between 2800-3000, but with sudden bouts of noise that often cause resyncs at a very low level.

This is a line that has a long history of problems and many BT engineer call outs, so I do not want to risk another BT call out before first categorically satisfying myself that absolutely everything at my end is working correctly, hence my need to know how to test micro-filters.

[Rik]

I don't think it's really possible to test them without specialist knowledge and equipment. I should imagine, but am probably wrong , that you'd need to apply a series of tones in the audio and ADSL spectrum, and see what percentage breaks through.

[Lance]

I think the only way us end users can test them is by replacing them and seeing if the problems goes away. If it does, the old filter is faulty!