The NMEA interface is used for early model Garmins and other makes of GPS.
If waypoints are to mark the points of an object (i.e. a paddock or pipeline), you will need to plot these points onto a Points layer. Then, having created a polygon/lines layer, trace over the points when drawing on the polygon/lines layer.
Alternatively, you can select a polygon/lines layer if the waypoints/track file you are downloading are to form the one object only. This will automatically create the object when downloaded. You will need to stop the GPS transmission between each object.
