There is an analysis of the detectability of human radio signals at: http://www.faqs.org/faqs/astronomy/faq/part6/section-12.html http://www.faqs.org/faqs/astr

There is an analysis of the detectability of human radio signals at: http://www.faqs.org/faqs/astronomy/faq/part6/section-12.html http://www.faqs.org/faqs/astronomy/faq/part6/section-12.html The main uncertainty is at estimating the level of radio technology that can be available to alien civilizations.