Equipment employing new cross-correlation design concepts for receiving and processing weak rf signals in a noisy environment is described. It is shown how this equipment becomes an integral part of the instrumentation for measuring the differential phase between the ATS-6 satellite 40- and 360-MHz coherent cw signals that have been propagated through the ionosphere. The relationship between 40-MHz phase and amplitude scintillation was developed using differential phase data from the ATS-6 geostationary satellite. The 40- and 360-MHz coherent signals were propagated through the ionosphere and received on the 150-ft radio telescope at the Sagamore Hill Radio Observatory. The influence that the traveling ionospheric disturbances (TID) have on the phase of the 40-MHz signal receives special emphasis, and it is shown how the presence of TID aids in the analysis.