KP4AO Arecibo Observatory QSL Posted by myradiowaves on 12 Novembre 2017 Posted in: Ham. Tagged: Arecibo Observatory, KP4AO, qsl. Leave a Comment Paper qsl of the research campaign in July 2017 of the Arecibo Observatory on the HF frequencies 5.125 and 8.175 MHz. Report sent with SASE to the manager W3HNK an received in 4 months.