A 12 MHz radio path over 2000 km has been used to examine the stability of the transmitted frequency over intervals of time generally frequency over intervals of time generally needed to take a sea state measurement of the ocean surface on a radar backscatter experiment. The variance of observed ionospheric Doppler shifts during successive 100 second intervals is about 0.04 Hz for one hop, point to point propagation predominatly through the F layer. This is expected to double for backscatter paths and to be directly proportional to the carrier frequency. Although the observations apply directly to only one ray in the radar beam and exclude mixed modes on the return the second-order spectra from which sea state conditions may be calculated.