'Yet' is a weird term to start that sentence with. 'As expected' would be a better fit.
You showed us the schema where [call_sign] does not permit nulls, then you showed us an error you got when you tried to put a NULL value into [call_sign]. Seems pretty straight forward.
I would use the wizard to import the file into a new table (
https://docs.microsoft.com/en-us/sq...import-flat-file-wizard?view=sql-server-ver15). Once imported you can verify issues and build a query around anything preventing the direct importation. THen you can turn that query into an INSERT INTO and move the data into the actual table you want that data in.