Revision method to aproximation multinomial with equal amplitude

In work shown the low efficiency of the using the modern generator of measuring signals for measurement of the frequency features in the field of infra low frequencies. It is offered to using signal on base of the trigonometric multinomial with even discrete spectrum and method to his aproximations. The are received analytical expressions of the discrete harmonic spectrum of approximating function. Is offered method of the estimation of inaccuracy of the approximation in the manner of ratio of the harmonicas of the stray spectrum and unevenness of amplitudes spectrum in workspace of frequencys.