Propagation management for no acknowledge HF links

The problem of propagation management of HF communications circuits is discussed for the no-acknowledge case, i.e., where no reply is possible from the receiving terminal. In such a case propagation management relies heavily on the accuracy of predictive models of the ionosphere. Allowance for both the deviations of the actual behavior from the prediction and the effects of probable noise and interference at the receiver must be made in the communications equipment configuration and information controlling software. Topics discussed include: pre-1979 tests, prediction performance, scaling of ionograms, equipment control and data logging. The present method for transmission of Naval messages without acknowledgement is the HF Fleet broadcast; multichannel low-speed telegraphy is converted to tone pairs and frequency division multiplexed onto 3-kHz single sideband channels which are simultaneously transmitted at a number of radio frequencies (normally 7 or 8) from stations at Canberra and Darwin.