I reckon my line loses around one eighth of its capability from that notch, so it can be quite an impact.
The power notching is specified in the NICC's ANFP, ND1602 v5.1.1,
http://www.niccstandards.org.uk/publications/llu_spec.cfmI've attached the appropriate graph from the ANFP - where the different coloured lines give 5 example power masks (ie max power limits) for 5 different cabs. It shows 5 of the 26 different settings; my
very rough rule of thumb is that a CAL of 10 maps to 1km of exchange-cabinet distance for standard 0.5mm copper (the CAL is actually attenuation at 300kHz, in dB).
- Pink line: CAL=50, approx 5km full notch, trough at 0.5MHz, like @BE1's
- Blue line: CAL=40, approx 4km, full notch, trough 0.6-0.8MHz
- Light blue line: CAL=30, approx 3km, full notch, trough 1.1-1.2MHz
- Green line: CAL=20, full notch, trough 1.5-2MHz,
- Yellow line: CAL=10, partial notch at 2MHz
- Red line: CAL=0, outside the exchange, no notch
When looking at the variations, the CAL=20 notch looks worst to me, but I could be wrong - I hate trying to interpret logarithmic graphs.
My notch looks very much like CAL=25ish, but the distance could be as little as 1.4km ... but I'm pretty sure the lines are only 0.4mm copper, which will skew things.