This paper reports the emission at 237 MHz of the activity centre located in the McMath zone 11482 during its passage on the solar disc, from 17 to 31 August, 1971. During this period it has been practically the only active group from the radio point of view.
The instrument of the Trieste Astronomical Observatory is a radiopolarimeter working at 237 MHz from which we can obtain with high time resolution the two circularly polarized components of the solar radiation. From the characteristics of the radiometer the accuracy in the computation of the degree of circular polarization can be generally considered to be better than 10%.
Before and after the passage of the active centre on the solar disc the emission was decreased to a minimum level (12 solar f.u.) and during the passage a strong noise storm developed which continued almost every day. The maximum of the emission was on August 24 at 13 h 30.36 m UT, with a flux density of 546 x 10 -2z W Hz -~ m -z. The behaviour of the daily mean emission during the whole passage of the source shows a marked directivity, typical, on the other hand, of noise storms.
For what concerns the polarization, it may be of interest to consider its behaviour in the days during which there was more variability, that is August 23, 24, 25. During the other days the polarization percentage was rather stable, at about 50% left. Figure 1 shows the behaviour of the degree of circular polarization during these days, together with the correspondent behaviour of the flux density of the total emission. August 24's emission needs a particular consideration. During the second part of August 23 and at the beginning of August 24 the emission presented a change in the polarization, while type I bursts were still present with a left handed circular polarization. From 9 h UT of August 24 the emission increased strongly, being again lefthanded polarized, while type I bursts disappeared completely. For a period of about an hour, between 14 h and 15 h UT, while the emission decreased slightly and there was also a decrease in the polarization, type I bursts reappeared, but now completely unpolarized. After 15 h UT the polarization and total emission increased and type I bursts disappeared again.
As far as the localization of the emission is concerned, interferometric measurements at 169 MHz and 408 MHz made in Nancay (see Solar-Geophysical Data 325, I) show two different sources, located approximately above the preceding and the following spot of the group. Furthermore, the fluxes measured at 169 MHz show that the preced-Solar Physics 30 (1973) 159-161.