Concerned is a spectral profile of electromagnetic (EM) emission from a signal line on a high-speed digital circuit. The authors have proposed and examined an a priori method to predict the peak frequencies on spectral profile of EM emission from printed circuit boards (PCBs). Profile of an EM spectrum is determined by the resonance of digital circuits. It is the purpose of this paper to investigate the parameters that determine the spectral profile of EM emission from a signal line on a PCS. In this paper, measurements and calculations of EM spectra were carried out for different load capacitances. EM emissions were measured with a small loop antenna at a 50mm from the surface of the PCB. Measured EM spectra had two peaks. Calculated EM spectra, which was based on transient current given by the analog simulator SPICE, had two peaks too. Results of calculations of EM spectra for different internal capacitances of an IC tell that lower peak frequency is determined by the resonance frequency of the resonant loop which is composed of an IC package and a decoupling capacitor. Comparison with measured EM spectra and calculated EM spectra for different load resistances tell that sharpness of the other peak depends on Q factor of a resonant loop which includes a signal line. Therefore the peak frequencies of EM emission spectrum can be predicted as two resonance frequencies of two resonant circuits.