Broadband power line communication (PLC)has attracted attention by promising very high data rates along with ubiquitous network providing connectivity points in the houses and buildings connected to the grid in the most cost effective way such that no extra costs of installations are incurred. However, since broadband PLC occupies a very limited frequency band, it is forced to coexist with numerous powerful licensed communication systems transmitting in the same band. The interference caused by these systems may complicate or even block data transmission in the power line network channel. In literature, there is a considerable amount of work regarding narrowband interference (NBI)suppression. Most of the proposed methods, which can be classified as NBI avoidance and NBI cancellation techniques, require interference statistics. In this paper, we perform measurements in the frequency band of 1-100 MHz with an aim to identify and evaluate NBI levels above the power line network noise floor by assuming some preliminary information about the possible sources of NBI.