 Thus, ground dipoles are sited over low conductivity underground rock formations (this contrasts with ordinary radio antennas, which require "good" earth conductivity for a low resistance ground connection for their transmitters).The two U.S. Navy antennas were located in the Upper Peninsula of Michigan, on the Canadian Shield (Laurentian Shield) formation, which has unusually low conductivity of 2×10−4 siemens/meter.resulting in an increase in antenna efficiency of 20 dB.