Characteristics of radio signals during the sounding of Halley's comet

Experimental data are presented on variations of the phases and frequencies of coherent radio signals in the decimeter and centimeter wavelength regions emitted from the Vega-1 and -2 spacecraft. Results of calibration measurements obtained during the period from February 14 to March 17, 1986 are compared with the results of the radio sounding of Halley's comet on March 6 and 9, 1986. It is shown that the effect of the plasma shell of the comet on radio wave propagation is commensurate with that of the interplanetary plasma. Quasi-periodic (with a period of about 30 sec) signal fluctuations were identified during the flight of the Vega-1 through the cometopause.