Lowering the base frequency of AEM systems is important for increasing depth of exploration in conductive terrain, but is difficult because receiver coil motion noise dramatically increases noise levels. By re-designing the receiver coil and coil suspension, the receiver coil motion noise has been largely eliminated in the Helitem35C system. In this paper we compare survey data acquired at 30 Hz with 15 Hz and 7.5 Hz data. In order to generate appreciable ground signal at 7.5 Hz, a 50% duty cycle square pulse has been used. The survey data had signal well above noise levels to the 30 ms channel centre time possible with the 7.5 Hz, providing greater depth of exploration and better interpretation of conductors.


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