[Pisces]

If it is just a line then it would simulate the radio direction finder. As the circle antenna would not really be able to give you distance, only direction. Signal intensity would be quite hard to transform in to a distance, since the many unpredictable factors in radio wave propagation. That's why the big thing is triangulation, directions from different stations intersecting near the source. From a single Uboat or ship, the best you can do is simply move towards the line. That loop antenna can actually not distinguish if the radio source is in front of it, or if it is behind it. So you really would have to consider both directions.

If you get an icon on the map with course and speed and time indication then it is just a radio Intel report. Imagine there being German scoutplanes or simply BdU telling you what it found out from whatever sources it got. Convoys get radio messages as text accompanied with them. You know, the ones that show up in some menu. Single opportunity ships just show up on the map, bit still have those details when you hover or click on it. Speed being show as a rough estimate range.

If you see an icon on the map fairly close to you then it is likely within visual range and a sighting of the crew, or radar if you have it. It doesn't show speed or time, or course as text. At best you could tell course by the way the icon is pointing.