What I mean is a logbook entry stating that the installation was performed using approved data - the ELT manufacturer's installation instructions, AC43-13, aircraft manufacturer's maintenance manual or TN etc. The sorts of things that the document you linked to talks about. I would like to find something like that that states an antenna installation that's practical in a non metal glider is OK. As yet I haven't and as far as I can tell it would be contrary to the ELT manufacturer's installation instructions and the linked AC seems to state that if one does that it is no longer a minor mod. There's a DG TN about 406's but it's not available online so I don't know what's in it.