here with have a 1989 Emmelle Cortina XL that iv been chipping away at for a few years, the only original parts are the frame, axle, chainset, stem,seatpost, front mech. after finding the bike at my local landfill i liked the frame and new i had to do something with it. i will upload more...
looked once more on my archive of old catalogs,
DB had till 1987 a rather handwriting-style font for the Diamond Back main decal (like this one from 1987)
The 1988 line up had the new Diamond Back main decal font, but all bikes had u-brakes at the chain-stays.
So if it's at all a DB, i do meanwhile question this, it has to be from 1989 or later.
As said by @Rampage DB seem to have never used an internal cable routing. Also the drop-outs of your frame are a bit strange, look like low end models but the eyelets are missing.
Maybe a Curaca from 1989 (was available in red too) and one of the rare ones with rear brake at the seat stays.
But tube diameter looks smaller, and sure, with changed cable routing for the rear brake and eyelets removed?
Especially the internal cable routing outlets look very professional, rather than done at home...