save nat file (not complete)

[peterdudfield]

Pull Request

Description

Save .nat file for 5 min data

Fixes #

How Has This Been Tested?

CI tests

• [ ] Yes

Checklist:

• [ ] My code follows OCF's coding style guidelines
• [ ] I have performed a self-review of my own code
• [ ] I have made corresponding changes to the documentation
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have checked my code and corrected any misspellings