An article by Massimo Biondi (in Italian) about telepathic experiments utilising radio broadcasts mentions the SPR:
https://psireport.wordpress.com/2017/12/27/radio-esperimenti-di-massa/comment-page-1/#comment-198
The experiment reported in the SPR's Proceedings can be found in vol, 38, in an article by V J Woolley: 'The Broadcasting Experiment in Mass-Telepathy'. It took place on 16 February 1927 The article can be read in the SPR's online library.