The book answer is ... about a foot off the ground to cancel EMI. However... i prefer to noise cancel at swinging height. Why? because the noise cancel will set the channel being used and those 28 freq that are randumly chosen. For me, i dont see how i can get the best channel without it knowing what the ground conditions are. Each channel has 28 freq... but unlike the SOV which has its freqs set at 1.5 kHz intravals, the Explorers isnt a set freq apart. It could set them on the high end or low end depending on the EMI.... without knowing the ground conditions? The wrong choice may have dramitic affect on the depth.