A Single-Antenna Repeater for HF Radio Propagation Studies.

摘要

The purpose of the work was to develop and test a compact, portable, calibrated single-antenna repeater which has application to HF radio propagation studies. For example, high-frequency backscatter ionograms--depending on the terrain-generally show one or more discrete range intervals where the returned energy is appreciably greater than the general noise-like return from other ranges. The ground features which cause these areas of enhanced HF energy reflection are not as yet fully understood. A portable repeater is capable of being operated in those areas where such reflections exist so that a direct comparison can be made between the repeated signal and the natural echoes. The repeater described in this report is especially useful with FMCW sounding waveforms. A fundamental problem in building any repeater is the avoidance of oscillations when it is attempted to retransmit an amplified signal with receiving and transmitting antennas in the same locality. The solution adopted in this case consists of switching one antenna rapidly between transmitting and receiving modes. The received signal is amplified, then stored for the duration of the receiving period. At the end of that period it is transmitted. The act of switching in this way does not seriously degrade the operation of the repeater; in fact, it confers certain unique advantages. (Author)