The H20 (particularly the H20-600) is known to have a much better tuner than the HR20, particularly in its performance in a multipath environment. The sort of signal fluctation you see on the HR20 is typical of multipath.vernonator said:
Multipath is a very common problem with indoor antennas. You may find the reception changes when you swap antennas, since each antenna will have its own multipath issues.