Hello Gilles
This seems to be a part of the Peil G6 radiocompass. This specific box (KAgK6) is located between the antennas and the electronics, and was intended to optimize the signal transmission. You can find a manual of the Peil G6 here :
https://www.cdvandt.org/D-Luft-T-406...er-PeilG-6.pdf (the description of the box is included).
Have a nice confined day !
Jean Schreiber