Estimation of the availability of data modems on oblique high latitude HF paths

The performance of beyond line-of-sight (BLOS) high frequency (HF) communication systems is dependent on the match between the system and the propagation environment. Antenna gain and transmitter power, and consequently the received signal to noise ratio (CNR), are very important in this respect. However, the match between the signalling waveform and the time and frequency spread characteristics of the propagation path often deserves equal or greater attention. This paper is based on the analysis of data collected by a channel sounder known as DAMSON (Doppler And Multipath SOunding Network) which can characterise the narrow band HF channel (3 kHz) by measuring its scattering function. The system uses low power, pulse compression waveforms and makes extensive use of digital signal processing techniques in order to measure, in real time, the signal time of flight, multipath spread, Doppler spread and shift, and signal strength over communications paths. The DAMSON system operates from remote sites on pre-selected frequencies ranging from 2 to 30 MHz