The "Erstling" IFF transceiver was activated from ground stations by switching the pulse repetition frequency from 3,750 Hz to 5,000 Hz. The on-board device replied by sending a pre-programmed morse code signal on 156 MHz. The coding unit was a motor-driven cam switch encrypted with two ten-bit code keys. Würzburg stations needed to be equipped with accessory units, namely a query transmitter code-named Q-Gerät ("Kuh", German "cow") and the identification receiver "Gemse" (German for "chamois").