A communication system transmits data signals between communication nodes. A first data signal is transmitted as an electromagnetic wave along a first data transmission path to a receiver using skywave propagation. A second data signal, identical to the first data signal, is transmitted to the receiver along a second data transmission path. The two data signals are compared at the receiver to determine any distortion caused by the skywave propagation. Data regarding the distortion is sent back to the transmitter so that subsequent transmitted data signals may be preconditioned when sent by skywave propagation.