SMO 1932 Sweden

The call is SMO (Sugar Mike Oscar), not SM zero.

This was an experimental station och the Frösö Island in the lake Storsjön, close to the city of Östersund, apparently in connection with a camping ground.
It was not a ham station, although they were allowed to work hams.
The Swedish PTT had issued a few three-letter calls around 1930. They all disappeared before WWII.

QSL Patrick Rigg Collection
Info courtesy of SM6JSM