Re. Unid 520 kHz: https://mediumwave.info/2023/09/15/unid-39/
“By the way, 520 kHz used to be a German frequency because the Copenhague Plan (1948) did not allocate many/enough frequencies to Germany. The Germans, who were only represented by the Allied powers, called it „Wellendemontage“.

I was also listening to 520 kHz when I was on holliday in Passau long time ago.
As a former member of german radio monitoring I can tell you that the reason for giving up this frequency was the allocation of the international NAVTEX system on 518 kHz. Mode is Sitor B (broadcast), a forward error correction system.

Walter Barteczek (2023-09-15)