These codes are often implemented in concatenation with a hard-decision code, such as Reed Solomon.
A convolutional code is specified by:
n: number of output bits
k: number of input bits
m: number of registers
The following picture shows a (2, 1, 3) convolutional encoder with generator polynomials G1 = 111 and G2 = 101 :
The graph of the convolutional encoder is presented in the following picture :