The Industry standard cable for SDI is Belden 8281, which is a solid core, twin screened co-ax. The spec using this cable should allow transmission of 200 meters plus without losses.
Over shorter runs ANY reasonable quality 75 Ohm co-ax should be fine - but avoid RCA cables and adapters, use directly crimped BNC on both ends.
Hope this helps
Richard Ansell
Snell & Wilcox