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80 lines
2.9 KiB
Text
80 lines
2.9 KiB
Text
/*! \page page_gpsdo_b2x0 Internal GPSDO Application Notes (USRP-B2x0 Models)
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\tableofcontents
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This application note describes the use of integrated GPS-disciplined
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oscillators with Ettus Research USRP devices.
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\section gpsdob_specs Specifications
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- **Receiver type**: 50 channel with WAAS, EGNOS, MSAS
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- **10MHz ADEV**: 5e-11 over \>24h
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- **1PPS RMS jitter**: \<50ns 1-sigma
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- **Holdover**: \<20us over 3h
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<b>Phase noise</b>:
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Offset | Phase Noise Power
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---------|-------------------
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1Hz | -65dBc/Hz
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10Hz | > -102dBc/Hz
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100Hz | -132dBc/Hz
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1kHz | -148dBc/Hz
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10kHz | -152dBc/Hz
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100kHz | \< -155dBc/Hz
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<b>Antenna Types:</b>
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The GPSDO is capable of supplying a 3V for active GPS antennas or
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supporting passive antennas.
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\section gpsdob_install Installation Instructions
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To install the GPSDO, you must insert it into the slot on the board near
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the 10 MHz Reference SMA. Keep in mind that the two sides of the GPSDO
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have a different number of pins. When inserting the GPSDO, make sure to
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press down firmly and evenly. When turning on the USRP B2X0 device, a
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green LED should illuminate on the GPSDO. This signifies that the unit
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has successfully been placed.
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<b>NOTE: The pins on the GPSDO are very fragile. Be sure to press down
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evenly, or the pins may bend or break. Once the GPSDO is in place, we
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very highly discourage further removal, as this also risks damaging the
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pins.</b>
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\section gpsdob_using Using the GPSDO in Your Application
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By default, if a GPSDO is detected at startup, the USRP will be
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configured to use it as a frequency and time reference. The internal
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VITA timestamp will be initialized to the GPS time, and the internal
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oscillator will be phase-locked to the 10MHz GPSDO reference. If the
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GPSDO is not locked to satellites, the VITA time will not be
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initialized.
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GPS data is obtained through the **mboard_sensors** interface. To
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retrieve the current GPS time, use the **gps_time** sensor:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
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usrp->get_mboard_sensor("gps_time");
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The returned value will be the current epoch time, in seconds since
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January 1, 1970. This value is readily converted into human-readable
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format using the **time.h** library in C, **boost::posix_time** in C++,
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etc.
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Other information can be fetched as well. You can query the lock status
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with the **gps_locked** sensor, as well as obtain raw NMEA sentences
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using the **gps_gprmc**, and **gps_gpgga** sensors. Location
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information can be parsed out of the **gps_gpgga** sensor by using **gpsd**
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or another NMEA parser.
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\section gpsdob_power Using a power supply with the B2x0 and GPSDO
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The GPSDOs for the B2x0 draw extra power, and when running off of bus power
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only, brownouts are possible (although not guaranteed to happen).
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It is recommended to use a wall power connector when using a B2x0 in
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conjunction with a GPSDO.
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*/
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// vim:ft=doxygen:
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