I asked on here a while ago about getting a first GPS.  In the end I found a new Trimble 250, with the DGPS antenna.  I really couldn't see where the additional cost of a fancier unit was justified when the only use I currently see for it is guidance.  Thanks to all for the replies.

Does this antenna function like a cell phone booster on a vehicle, and it works best surrounded by a flat surface to bounce the signal to?  such as in the middle of a flat roof? The reason I ask is if I want to mount it on the quad to go mark obstacles, boundaries, manure application areas, drainage etc,  can I just stick the antenna where ever, or will it need a big flat surface to function properly?