On the Trimble Ezee Guide 500. Happened occasionally before but today was a lot more frequent. Ever few minutes it says "GPS signal has degraded". Then a few seconds later it says "GPS is now ready for use". During these intervals It keeps painting the coverage all the time so I can see what I have done but does not draw a line for the next pass. Odd thing is that it worked perfectly on the drive home at 16 mph. Speed makes a difference?