The GPS receiver in Raveon’s M7 and Atlas PL GPS transponder may be configured for different situations. By default it is configured for LAND operation.
Selecting the correct operating parameters has a significant impact on GPS receiver performance. GPS receiver dynamics may be optimized for LAND, AIR, or SEA operation.
LAND = 1 Maximum speed the GPS will receive at is 233knots/268mph/430kmh. Useful altitude from -2000 to +9000 meters.
SEA = 2 Maximum speed the GPS will receive is not specified. Useful altitude from -2000 to +9000 meters.
AIR = 3 Maximum speed the GPS will receive at is 1000knots/1150mph/1800kmh. Useful altitude from -2000 to +50,000 meters.
The default setting for the GPS receiver used in Raveon’s M7 series of GPS transponders and Atlas PL Transponders is LAND.
The default LAND operating parameters allow the receiver to perform well in most environments. Transponders with firmware version C12 or higher are able to view the GPS receiver’s configured dynamics, and change the dynamic mode between AIR, LAND, and SEA. Upon power up, the firmware reads the internal GPS receiver’s current configuration.
The user can optimize the internal GPS receiver in the transponder to a particular application. If the receiver is then taken out of this environment, the specifically tuned receiver may not operate as well as a receiver with the default options.
The dynamics feature default setting is LAND mode, where the receiver assumes a moderate dynamic environment. In this case, the satellite search and re-acquisition routines are optimized for vehicle type environments. In SEA mode, the search and re-acquisition routines assume a low acceleration environment. In AIR mode, the search and reacquisition routines are optimized for high acceleration conditions.
Reading the GPS Receiver Configuration
The GPS receiver configuration may be determined by using the GX command to show the overall configuration of the M7 or Atlas PL transponder. The “Dynamics” command will also return a string in the following format that indicates how the GPS receiver in the transponder is currently configured.
MMM, EE.E, SS.S
MMM: dynamic mode AIR, LAND, or SEA
EE.E: Elevation Mask
SS.S: Signal Mask
This is the minimum elevation angle for satellites to be used in a solution output by the receiver. Satellites which are near the horizon are typically more difficult to track due to signal attenuation, and are also generally less accurate due to higher variability in the ionospheric and tropospheric corruption of the signal. When there are no obstructions, the receiver can generally track a satellite down to near the horizon.
This mask defines the minimum signal strength for a satellite used in a solution. There is some internal hysteresis on this threshold which allows brief excursions below the threshold if lock is maintained and the signal was previously above the mask.
Configuring the Dynamics
Use the DYNAMICS command to set or read the dynamics. DYNAMICS with no parameter will return the configuration. The following commands may be used to set the dynamics:
DYNAMICS 0 (factory default dynamic mode)
DYNAMICS 1 (LAND)
DYNAMICS 2 (SEA)
DYNAMICS 3 (AIR)
When issuing the DYNAMICS x command, give the GPS receiver a few seconds to execute it. The M7’s firmware will also send a “flash save” command to the GPS receiver after the dynamics configuration is changed so that the change becomes permanent in the GPS receiver. Upon power-up, the GPS receiver will use the new dyncamics setting.
To verify the dynamics setting was saved, cycle power on the M7 or Atlas PL, enter the CONFIG mode, and enter the GX command to view the overall configuration of the device. The GPS receiver dynamics will be displayed.
Advanced GPS Receiver Configuration
To facilitate the advanced user, Raveon added a command “PASS” in the C12 firmware. PASS will pass the parameter of the command to the internal GPS receiver in NMEA format. The GPS receiver used in the M7 transponder and ATLAS PL personal locator is a Trimble Copernicus II. The technical manual for the Copernicus II contains details on how to configure it using NMEA type messages.
For example, to set the GPS receiver to AIR mode, issue the following command while in the command mode.
The command’s paramter is a NMEA formatted sentence without the * or the checksum. The M7 or Atlas will append the * and the checksum to the sentence before sending it to the internal GPS receiver. To set the dynamics, use the DYNAMICS x command, not the PASS command. The PASS command is provided to the advanced user who wished to reconfigure the receiver’s low-level configiruation paramters such as signal and elevation masks.
If you change the GPS receiver’s configuration with the PASS command, do not forget to issue the save configuration command to the GPS reciever. The save command for the GPS receiver in the M7 and ATLAS PL is: