As per @Andrew116 prompting, played around with. It works, so put here for easier finding in the future! 
Here’s my super simple steps:
Step 1. Fit a U22.A Jammer on your Viggen.
Step 2. Right console, Jammer mode selector to ‘A’, Jammer channel to ‘K’. Bork Bork!
Step 3. Fly around and pick up signals, but don’t die. Go Fast Mr Rabbit!
Step 4. Land. System into ‘BER’. Open up kneeboard and the ELINT page shows the Lat/Long boxes.
There should be a file in DCS AJS37 folder ELINT.info that contains all the text info, with emitter number, the frequency detected (so you can tell what it is), how long you heard it and the ‘box’ coords.
EDIT: ELINTData.info is found in your ‘Saved Games’ DCS_AJS37 folder. Create one first I guess, although mine already was there from Simple Radio.
To plot it nicely on a map, a bit of code, e.g.
Example ELINT line from video:
NW 43,32,10 040,07,39 SE 43,12,12 040,24,40 (two sets of degrees, minutes and seconds).
So that’s 43.53611111, -40.1275 by 43.20333333, -40.41111111 decimal for our box (top left, bottom right).
With a bit of Google Maps API it looks like:
Example code to play around with here:
Fun stuff! 