Praise be to Allaah.
It was reported that the Prophet (peace and blessings of Allaah be upon him) gave orders that the call to the eclipse prayer should be made by saying “Al-Salaatu jaami’ah”. This was narrated by al-Bukhaari and Muslim. The Sunnah is for the caller to repeat that until he thinks that the people have heard; there is no set limit for that as far as we know. And Allaah is the Source of strength.