This paper presents two novel interference measurement estimators for the DRM (Digital Radio Mondiale) system. They are based on the PSD (Power Spectral Density) estimation of the received spectrum, and provide interference estimation whilst the DRM transmitter is in operation. The first estimator provides successful detection of in-channel narrowband interference. If the interferer is an AM co-channel signal, the second estimator takes advantage of the specific characteristics of the DRM modulation to provide accurate measurement of the signal-to-interference ratio value. This allows protection ratio calculus and failure detection caused by interference.