Apparent solution to upstream synch rate problems

[#1]

I only post this because it may be of interest to other users.
I have been struggling for some time with loss of upstream synch with the rate dropping from 448kbps at 20dB to as low as 128kbps at 6dB noise margin.
Changing filters and phones didn't solve the problem.
Having done a search on Google I found a number of reports where double filtering a fax machine solved a similar problem. Worth a try so I added an extra filter between my filtered faceplate and the phone and answering machine.
It has now held synch at 448kbps  for  over 5 1/2 days - still keeping my fingers crossed 
Edit - note I do not have a fax machine

[#2]

Thanks Jim.
That's certainly another one for the list.

[#3]

I've seen similar suggestions for Sky boxes and DECT phones as well.

[#4]

Still rock solid except the router decided to do a reboot yesterday - now connected at 448 / 3,488 with very few FEC errors and no problems.
Now to wait for 2 or 3 weeks to see if the automatic systems drop my default noise margin or I will again start ticket tennis in trying to get BT to alter it.

[#5]

Original post updated to make it clear - I do not have a fax machine but using Google that was where I found the original reference to double filtering

[#6]

Me and my big mouth 
weather changed and I have just had three resynchs at 224kbps at 7dB