Can anyone tell me if lengthening the cable from our satellite dish to
our digital TV set-up will lessen the quality of the reception?

At the moment the dish is attached to the chimney stack and drops
vertically from it, in a straight line, through the attic, through the
first floor, to the TV on the ground floor.

The chimney needs demolishing and rebuilding and we're thinking that
once that's done the house will look better if the dish is attached to a
gable wall. Not so obvious. But the length of the cable (travelling
horizontally along the length of the house before dropping much the same
distance as before) would then be twice the length it is now.

Will this lessen the quality of the reception? Much?

Eddy.