Multipath and Doppler observations during transatlantic digital HF propagation experiments

Digital HF transatlantic propagation experiments between two nodes at Dourbes, Belgium, and Needham, MA, using identical digisonde 256 systems became operational in October 1983. Adaptive two way sounding and real time channel evaluation studies are to be conducted among the network's nodes. Presently, the Dourbes station is transmitting 10 kW pulses using a horizontal rhombic antenna while the Needham station uses a long-periodic antenna for both transmission and reception. Amplitude and Doppler shifts of different multipath modes were measured during magnetically quiescent and disturbed periods for the first month of operation. The pulse modulation enables clear separation and identification of the multihop paths. Real time discrete Fourier transforms determine the Doppler shifts imposed by height changes of the reflecting ionospheric layers. A comparison of the observed MUF's of the dominant 2F mode with the MUF's predicted by the IONCAP model show the latter to be about 20 to 30% higher.