Very wide band pick-ups

After a brief recall of some basic definitions wide band monitors of different type will be reviewed. I will classify them according to nature of coupling: resistive, capacitive and electromagnetic. The last class is by far the most colourful and is subdivided into single monitors, signal power adders and coherent signal voltage adders. Pure magnetic monitors are not considered. The single monitors are intended for coherent high frequency signal observations, while the adders are intended for weak incoherent high frequency observations.