  We report experimental results of low temperature magnetotransport in high
mobility 2D electron systems exposed to radiation up to 20GHz frequency using a
simple dipole configuration. Magnetoresistance oscillations are observed as in
previously reported higher frequency radiation on 2D systems, however minima
here can be seen to extend to negative biases, and zeroes previously reported
are not observed persistently around the full sample perimeters. In addition,
under radiation, voltages are observed from internal to external contacts in
the absence of applied driving currents not due to simple rectification. These
findings are consistent with micro- and macroscopic theoretical pictures of
radiation induced transport and current instabilities due to local negative
resistivities. However, the temperature dependent development of minima is
shown to be severely power dependent, and outside of present theoretical
understanding.
