Studies of the fine structure of the object 1803+784

We have investigated the fine structure of the object 1803+784 at a wavelen gth of 18 cm with an angular resolution of similar to0.5 mas. The structure consists of a core (injector) and a jet. The angle of the relativistic pla sma outflow is equal to the angle of a conical diverging helix-the trajecto ry of compact components, suggesting a similar shape of the jet. The helica l structure and the curvature of the jet axis are assumed to be determined by rapid and long-period precession of the rotation axis. The core radio em ission at 18 cm is attenuated by absorption in the ambient ionized medium ( cocoon wall) by >25 db. The bright compact component is the nearby part of the jet extending outside the dense part of the screen. Ionization variatio ns in the medium cause low-frequency radio variability. Screen parameters a re estimated. (C) 2001 MAIK "Nauka/Interperiodica".