It is disliked for a person in a state of janabah to perform the adhan; because the effect of janabah appears in the mouth, preventing the utterance of revered remembrance, just as it prevents the recitation of the Quran, unlike minor impurity. The adhan should be repeated because it is meant to inform those who are absent, and it is possible that some may hear it while others do not, so repeating it is beneficial. See: Al-Bada'i 1: 149-152.