  We consider the modulated harmonic wave in the discrete series connected
Josephson transmission line (JTL). We formulate the approach to the modulation
problems for discrete wave equations based on discrete calculus. We check up
the approach by applying it to the Fermi-Pasta-Ulam-Tsingou type problem.
Applying the approach to the discrete JTL, we obtain the equation describing
the modulation amplitude, which turns out to be the defocusing nonlinear
Schr\"odinger (NLS) equation. We compare the profile of the single soliton
solution of the NLS with that of the soliton obtained in our previous
publication.
