30 We have learned with not little joy that your press is a sturdy champion of Catholic principles, that the Marconi Radio, whose voice is heard in an instant round the world - marvelous invention and eloquent image of the Apostolic Faith that embraces all mankind - is frequently and advantageously put to use in order to insure the widest possible promulgation of all that concerns the Church, and We commend the good accomplished. But let those who fulfill this ministry be careful to adhere to the directives of the teaching Church even when they explain and promote what pertains to the social problem; forgetful of personal gain, despising popularity, impartial, let them speak "as from God, before God, in Christ" (II Corinthians II: 17).
Source: Sertum Laetitiae (Vatican.va)