SNR Margin reducing with time
Posted: Fri Apr 01, 2016 8:42 am
Hi,
I've noticed with my 7800DXL, while it stays connected the noise margin gradually reduces then stays at that reduced level until the next time it reconnects even though the speed may be the same. For example yesterday morning when I was doing some stuff the noise margin was just over 4, but after reconnection it was back to 6dB and in that case at a very slightly higher speed. Now 24 hours later the margin is back to 4.1dB. There's a general pattern of margin dropping over night and picking back up again in the morning, and quite a lot of bit swapping goes on.
Any idea what's going on? I was speculating maybe that it may be an issue with the bit swapping algorithm, that swapping backwards and forwards reduces the overall SNR, and it only gets properly reset by a new synchronisation. Doing a bit of research it appears that some modems only bit swap away from poor tones, and don't swap back if those tones subsequently become available - does anyone know if the 7800DXL behaves like that? It doesn't quite explain, because if the bit swapping was only one way I'd expect it to pretty much stop after a few days as it should have "found" all the tones that go bad and stopped using these.
Thanks, Tony S
I've noticed with my 7800DXL, while it stays connected the noise margin gradually reduces then stays at that reduced level until the next time it reconnects even though the speed may be the same. For example yesterday morning when I was doing some stuff the noise margin was just over 4, but after reconnection it was back to 6dB and in that case at a very slightly higher speed. Now 24 hours later the margin is back to 4.1dB. There's a general pattern of margin dropping over night and picking back up again in the morning, and quite a lot of bit swapping goes on.
Any idea what's going on? I was speculating maybe that it may be an issue with the bit swapping algorithm, that swapping backwards and forwards reduces the overall SNR, and it only gets properly reset by a new synchronisation. Doing a bit of research it appears that some modems only bit swap away from poor tones, and don't swap back if those tones subsequently become available - does anyone know if the 7800DXL behaves like that? It doesn't quite explain, because if the bit swapping was only one way I'd expect it to pretty much stop after a few days as it should have "found" all the tones that go bad and stopped using these.
Thanks, Tony S