A. V. Bogdanov, D. O. Puksa, Yu. V. Romanov, V.V. Fomin

The paper deals with state-of-the-art professional transistor HF radio transmitters with power of 1 kW and 5 kw and HF modem with data transfer rate up to 9600 bps in the band of 300-3400 Hz made by ONIIP. The authors pay special attention to the validity of requirements to nonlinear combinational distortions factor. Requirements of the modem to the reception and transmitting equipment are considered, importance of struggle against impulse noise at reception of a signal and correct realization of algorithms of automatic gain control (AGC) in reception and transmitting routes is marked. The distortions brought by the internodal link equipment of spased radio centres and critical at data transfer rate about 9600 bps in the band of 300-3400 Hz are marked. The tendency of replacement of tube device by transistor ones at power of about 1-5 kW is considered, the opportunity of border expansion of applicability of transistors up to 20 kW due to new element base is specified. The authors also show the replacement of OFDM modems by single-carrier modems when signal band is about several tens of kilohertzes. Combination of a modem, receiving and transmitting equipment as well as antenna feeder devices in adaptive reception and transmitting systems is considered as a perspective way of increase of communication reliability.