"A Linear Transponder for Amateur Radio Satellites" article by Dr. K. Meinzer, DJ4ZC, available https://amsat-dl.org/en/helaps/
"Lineare Nachrichtensatellitentransponder durch nichtlineare Signalzerlegung", Dissertationsschrift Physik Uni Marburg von Karl Meinzer, 1973, available https://amsat-dl.org/en/helaps/