In this paper, radiation from a PCB trace with broadband harmonic frequency signals is proposed. For the digital signal, there are high harmonic frequency component current. These current will cause the radiated emissions which is called electromagnetic interference. Some of the radiated emissions emit or couple from the PCB traces. It means that the PCB traces act as the antenna. We design some experiments to study and analyze the radiated emissions mechanism from 30MHz to 1000 MHz. The measurement was performed in 3-m semi-anechoic chamber. It's usually used for EMI test. We found the magnitude of emissions increase with the longer length of PCB traces below 500 MHz. But above the 500 MHz, the resonant frequency length and transmission line dominate the radiation. For this paper researching results can help the PCB design and layout engineers to choose the best trace length to reduce the EMI emissions effectively.