  Keeping the discretness of the reciprocal space we calculate the spectrum of
incoherent electron-hole excitations in the conducting Fermi liquids. The metod
is illustrated on the well-known jellium model within the random phase
approximation. It also leads to the formulation os a sum rule from which we get
the details os dispersion curve for the collective plasmon mode. The notion of
time averaging in the discrete approach is briefly recalled.
