The objective of this paper is to provide a framework by which jitter phenomena, which are encountered at the output signals of a head board in an automatic test equipment (ATE), can be st udied. In this paper, the jitter refers to the one caused by radiated electromagnetic interference (EMI) noise, which is present in the h ead of an ATE due to DC-DC converter activity. An initial analysis of t he areas of the head board most sensitive to EMI noise has been made. It identifies a sensitive part in the loop filter of a phase locked loop which is used to obtain a high frequency clock for the timing generato r. Different H-fields are then applied externally at the loop filter to verify the behavior of the output signal of the head board in terms of RMS jitter. As for RMS jitter measurements, a frequency domain m ethodology has been employed. A trend for RMS jitter variation with r espect to radiated EMI magnitude as well as frequency has been obtai ned. Also the orientation of the external H-field source with resp ect to the target board and its effects on the measured RMS jitter has be en investigated. For measuring the RMS value, a proper circuitry has been designed on a daughter board to circumvent ground noise and c onnectivity problems arising from the head environment.