A. D. Vinogradov, P. A. Mozgovoi

In article is organized theoretical and experimental study main radio parameters of the high frequency receiving channel of the small-dimensioned polarization HF radio direction finder on the base of the one round loop antennas with upper feeding. It is shown that antenna of such channel must be an active and non-resonance. The antenna amplifier must have high-resistance entry load, but its output resistance must be equal to a wave resistance of the feeder between antenna and receiver. The experimental study of the model active loop antenna is organized. The analysis has shown that for minimum possible level of the environment noise in HF range, necessary to take into account also internal noises of the receiving channel. For channel on base active loop antenna in real noise situation HF range using low-noise antenna amplifier integrated with loop radiator allows to improve sensitivity on field of the receiving channel and to elevate the acting height of the loop radiator for count of the optimum enabling the loop in scheme of the receiving channel. In scheme of the receiving channel with active loop antenna occurs the additional reinforcement, because the module of the factor of the fission of the voltage of the input divisor, formed impedance of the loop and input resistance of the amplifier, have units less because reactive parts of input impedance loop and input impedance amplifier have the miscellaneous signs. The antenna amplifier performs the role of uncording device, weakenning influence local subject, surrounding direction finder, and laying under surfaces on character of the receiving channel. The optimum size of the loop radiator for achievement of limiting importance of sensitivity on field equal approximately 0,5 m. The antenna amplifier for achievement of limiting importances sensitivity on field, alike for the whole HF range, must have a frequency slopping and be equal approximately 20 dB on lower and 7 db on upper frequency of the range. Article contains 15 figures and 18 bibliographic sources of the information.