Robert,
A few questions -
1. What mobile device are you using? Trimble nomad 800
2. What XY and Z coordinate systems are you using? HARN 83 Florida West Zone Foot, NAD 83
3. Are you using 'Height above ellipsoid' or 'Mean Sea Level'? Height above ellipsoid
4. If you're using MSL, did you specify a geoid separation value? There are online calculators which can give you the value for your location. We have a leica backpack GPS that we grab the NMEA 0183 stream via a serial cable. We have a VRS sytem for RTK
GPS Preferences > GPS Height tab > Geoid Separation. We have to post process the elevations, to be correct as per the grid (elevational geiod). We use 0 for the antenna height and geiod seperation. Because the anntenae height is already figured in teh NMEA stream
GPS Height
5. When you say that the values are high, are you determining this by prior collected data you know to be correct? When we post process, we get a geoid_ z values that when you add to the geiod grid you get the real elevation. Example: In 7.1 we got 5.3 for a elevation , with arcpad 10 we get 10.3. We have determined it is the actuall arcpad software causing this. We setup with 7.1 and 10 on the same spot, and the geoid_z was off. We are using certified benchmarks to test.
6. How long are you waiting on each point before you take it. Also, are you averaging? If you wait on a point for several minutes (even give it 10-15 minutes on a single spot as a test) does the accuracy of the elevation improve? We are not averaging, we use a VRS system with survey grade leica backpack, we wait until the accuracy is within .10 then take the shot, via the NMEA stream at the time
Thanks.