The density of FR4 is 1,850 kg/m^3. If we assume a PCB area of 12*50 = 600 mm^2...
For a 1.0mm PCB: 600 * 1.0 * 1.85 = 1.110g For a 1.6mm PCB: 600 * 1.6 * 1.85 = 1.728g
There doesn't appear to be much documentation for contestia...
Really we're looking at Olivia MFSK - contestia is just a variant.
It's already implemented in dl-fldigi here
(Inverse) Fast Hadamard Transform needed