In the framework of military or humanitarian operations, it is important to determine the geographic location of High Frequency (HF) transmitters by analyzing the emitted electromagnetic signals. This paper presents a time domain geolocation technique, exploiting the time of arrival of the radio signal received at a set of single antenna stations. A preliminary study showed that the location could be established without explicit knowledge of the ionosphere height. We present a measurement campaign designed to validate this approach, where HF stations are deployed in 5 sites in France. The ionospheric channel is regularly sounded at the frequencies of 6.40 MHz, 8.06 MHz and 9.95 MHz. This experiment allows analyzing the effect of the ionosphere on radio transmission, including the observation of the different propagation modes and the diurnal channel variations. The initial measurement results are then used to evaluate the performance and limitations of time domain HF geolocation.