I am receiving HF-Fax, RTTY and Navtex information from a simple SSB radio
linked to a PC with SeaTTY software.

Where can I find reading matter of very basic nature (for somebody who has
no previous knowledge) wherein I can find out about simple fundamentals.
E.g. 'Signal: white +425Hz'; F1B/C class emission; how to use parameters
such as AFC local and global deviation, effect of squelch and squelch
threshold; what is 'unshift on space', etc.? (I have ploughed through help
files which are no doubt useful for someone who understands basics, but not
very good as idiot guide).