There is no MacWilliams identity for convolutional codes (Corresp.)
James B. Shearer, Robert J. McEliece · IEEE Transactions on Information Theory · 1977
An example is provided of two convolutional codes that have the same transmission gain but whose dual codes do not. This shows that no analog of the MacWilliams identity for block codes can exist relating the transmission gains of a convolutional code and its dual.