A. V. Bogdanov, S. I. Kuzlyakina, D. O. Puksa, Yu. V. Romanov

Based on the complex approach to transmitting complexes of HF high speed data transmission links the paper proposes the optimization of requirements to high power transmitters allowing to reduce transmitter complexity and cost without essential decreasing the communication reliability. It is shown that IMD of no more than 42 dB PEP in the frequency range from 1.5 MHz to 30 MHz is achievable but on actual HF links using state-of-the-art modems providing data transmission rate up to 9600 bps within the 300-3400 Hz standard telephone channel it is sufficiently to provide IMD -36-38 dB PEP . The impact of the transmitter nonlinear transfer characteristic on the intermodulation noise level specified by it for different values of the amplified signal peak factors is analyzed. It is shown that as in the case for the 3rd order intermodulation products decreasing the signal power by 1 dB (increasing the peak factor by 1 dB) results in decreasing the intermodulation noise power relative to the signal power approximately by 2 dB. It is shown the importance of the transmitter AGC correct operation using high speed modems sensitive to excessive signal limiting and spurious AM. The problem of combining the transmitter powers is considered. Using a real transmitting system as an example it is shown that expenses for increasing the efficiency of transmitting antennas can be order of magnitude more effective way of increasing the radio link power than combining powers of two transmitters by the power combiner. It is also pointed out that when the ionospheric wave is used the transmitter power change by a factor of two (by 3 dB) is hardly appreciable from the point of view of changing the radio link proper functioning.