I have tested the NovAtel OEM 5 boards in several receivers (Viva, Carlson Surveyor GPS, X900) and while they have been okay in a matched base – rover pairs, they have not compared well to systems based on the Trimble BD970 boards or Spectra/Ashtech ProMark 800 receivers.
A week ago, I had an opportunity to compare a BD970 based receiver with a receiver using the NovAtel OEM 6 board under the big tree in front of our office. (I will describe the test I run in a moment.) Both receivers use exactly the same antenna element (in fact they are nearly identical.)
The OEM 6 is simply amazing. Solutions are really snappy. The ‘verified fix’ usually happens a few seconds after the initial fix. [For some reason, I find myself liking the dual fixing quite a bit. Especially when the verified fix happens so quickly. The OEM 6 really feels good under canopy.]
Here is a quick description of the test I run:
1. Corrections are served by the TURN VRS network in RTCM3 format with a virtual base 1-mile to the north. The corrections are played through a Pacific Crest UHF radio so that both GPS receivers under test get corrections at EXACTLY the same time.
2. I use two prism poles, 1 meter apart. The left pole is 1/2 meter lower than the right pole.
3. I wait for both receivers to fix, count to 5, store a single position, then dump both receivers, exchange positions and repeat. 60 times. So I have 30 occupations for each receiver on each pole. (I wait 5 seconds after the receiver fixes, independent of the other receiver.) If a receiver won’t fix in two minutes, I move it away from the tree, then sneak it back onto the pole.
The test location is, well, horrible. There is a giant tree 2-meters to the South, a two-story building 2-meters to the East, and big power lines to the west. The location is not suitable for GPS work. Which makes it perfect for testing receivers.
In the past, the OEM 5 boards have not fared so well in the Trimble VRS network. (The Trimble BD970 is matched to the Trimble VRS network and usually beats out every other receiver that I have tested other than the PM800 which either as good or better.)
But the OEM 6 has as good of performance as the BD970 based receiver. Absolutely.
What makes this remarkable and noteworthy is: the OEM 6 is about $1,200 less when bundled into a rover solution. Thats $2,400 for a base-rover pair.
Your takeaway should be: “Consider OEM6 based RTK GPS receivers. They are hot. Much better than the OEM 5 based receivers.”