I have an Atcom IP01 Asterisk box for VOIP which has a FXO module to connect to a POTS line. The phone line is either a long line or has some dodgy aluminium in it somewhere as the best synch speeds achievable are around 2.5Mbps once the SNR has been forced down (Billion 7800N router) - stats from the router:
Operational Mode ADSL2+
SNR Margin(Upstream) 6.3
SNR Margin(Downstream) 2.2
Line Attenuation(Upstream) 47.6
Line Attenuation(Downstream) 71.5
With the IP01 connected through a standard filter into the master socket, it forces the router a resync immediately and it will resynch around 1.6Mbps. Double filtering is forcing a resync to about 2.2Mbps.
I suspect this is down to additional noise the Atcom unit is putting onto the line, but a second unit is also causing the same issue so in theory should rule out faulty hardware.
Is there anything other than double or treble filtering that I could try doing to minimise the additional noise / immediate resync?