OT MF interference and ADSL {Was: Slow radio downloads - a bit off topic}

[Dave Liquorice]

On Wed, 19 Nov 2014 12:57:30 +0000 (GMT), Jim web wrote:

> Be interested to hear if anyone else has had the same sort of weird
> behavior that seems to be phased with sunset! 

ADSL is affected by interference from MF broadcast stations. During the day 
the ionosphere is "wrong" for the long distance recepetion of MF stations 
and you can only hear local stations via the ground wave.

At night the ionopshere changes and reflects the signals from MF stations 
over the horizon and you can receive them via the sky wave. Under the right 
conditions it's possible to hear east coast US MF stations in the UK. 
Normally all you can hear are stations from all over Europe.

This added "noise" at night can play merry hell with ADSL2 which uses 
frequencies from 125 kHz to 1.1MHz (or 2.2MHz for ADSL2+) for the downlink. 
The MF broadcast band covers 530 kHz to 1.6 Mhz.

I know if my ADSL resyncs during the day it'll do so at aroound 7 Mbps, come 
evening the noise will have increased and the error rate skyrockets, thus 
reducing throughput and causing the connection to drop, though unless it 
gets really bad it won't actually resync. Resync at night and it'll be just 
over 6 Mbps, this produces a stable connection day or night that is 
relatively error free.

What is a bit odd about your "fault" is the fairly regular timing. Sync 
during the day could well be way above what it can do at night hence the 
drop at sunset (though that seems a bit early). In the morning the reduced 
noise prompts the modem into resyncing at a high rate, ready for the 
evening...

Apart from the last 50 m or so our line is undergroud. I can imagine that a 
line with a lot of overhead would be far more sensitive to this diurnal 
change in noise level.

-- 
Cheers
Dave.