DGPS with two EM406A GPS units

Hi everyone.

I came across a section in the EM406A datasheet mentioning input from another GPS unit, thus enabling DGPS (http://www.adafruit.com/datasheets/em406a_ug.pdf - bottom of page 10).

Has anyone done this? Is it as simple as connecting the TX from GPS#1 to the RX of GPS#2?

I've been looking around on the net, but info is scarce.

Thanks! :slight_smile:

My understanding from a short read this morning of the literature http://solutions.seilerinst.com/Portals/1/Catalog%20Items/Mapping/WP_Delta.pdf suggests that one unit must be fixed and that the signals from two (or more) units can be combined to minimize statistical deviations.

With the new postprocessing engine, DGPS positions
at decimeter (10 cm/4 inch) accuracy are achieved
faster, at longer ranges from the base station, and
under tougher conditions than with older
postprocessing technology

I do not know if the above "postprocessing" could be done in near realtime via an RF modem. It is an interesting question. However, it was not that many years ago that GPS was actively "degraded" by the Air Force (May 2000.) I have read articles suggesting that the U.S. military and Homeland Security were concerned about ever increasing accuracy of small GPS units.... FYI.

Source: Center for International Stabilization and Recovery - JMU

Real Time DGPS
With this method, corrections are sent directly from the DGPS provider (or one’s own base station) to the rover unit in the field. This is usually used for navigational purposes and provides essentially instantaneous sub-meter positioning. In some areas of the world, the real time correction can be received from government broadcast stations using a small receiver which connects to the field GPS unit.
Post-processing is employed if the data does not need to be used immediately in the field. For the deminer, post-processing is recommended for two reasons. Post-processing is usually cheaper than real time DGPS and it enables the user to store files and stay organized. This method involves bringing the rover unit back to the base station (or laboratory where base station files are stored, or can be obtained) and doing the post-processing there.