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2be9d18ec4
* New method: --values="key1=value1,key2=value2" * To read key2: --values="key1=value1,key2,key3=value2" * Added --read-all option to read all values in EEPROM without burning * Old arguments still work but print deprecation warning Conflicts: host/docs/usrp_x3x0.rst
87 lines
3.5 KiB
ReStructuredText
87 lines
3.5 KiB
ReStructuredText
========================================================================
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UHD - Internal GPSDO Application Notes (USRP-N2x0/E1X0 Models)
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========================================================================
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.. contents:: Table of Contents
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This application note describes the use of integrated GPS-disciplined oscillators (GPSDOs) for
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the USRP N-Series and E1xx. For information regarding the GPSDO that is compatible with
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the USRP X-Series, please see:
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`USRP-X3x0 Internal GPSDO Device Manual <./gpsdo_x3x0.html>`_
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=======
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------------------------------------------------------------------------
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Specifications
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------------------------------------------------------------------------
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* **Receiver type**: 50 channel with WAAS, EGNOS, MSAS
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* **10MHz ADEV**: 1e-11 over >24h
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* **1PPS RMS jitter**: <50ns 1-sigma
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* **Holdover**: <11us over 3h
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* **Phase noise**:
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* **1Hz:** -80 dBc/Hz
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* **10Hz:** -110 dBc/Hz
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* **100Hz:** -135 dBc/Hz
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* **1kHz:** -145 dBc/Hz
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* **10kHz:** <-145 dBc/Hz
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**Antenna Types:**
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The GPSDO is capable of supplying a 3V for active GPS antennas or supporting passive antennas.
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------------------------------------------------------------------------
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Installation Instructions
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------------------------------------------------------------------------
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Instructions for mounting the GPSDO kit onto your USRP device can be found here:
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`http://www.ettus.com/content/files/gpsdo-kit_2.pdf <http://www.ettus.com/content/files/gpsdo-kit_2.pdf>`_
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********************************************
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Post-installation Task (N-Series only)
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********************************************
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**Note:** The following instructions are only necessary for UHD 3.4.* and below.
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This is necessary if you require absolute GPS time in your application
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or need to communicate with the GPSDO to obtain location, satellite info, etc.
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If you only require 10 MHz and PPS signals for reference or MIMO use
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(see the `Synchronization Application Notes <./sync.html>`_),
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it is not necessary to perform this step.
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To configure the USRP to communicate with the GPSDO, use the
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**usrp_burn_mb_eeprom** utility:
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::
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cd <install-path>/lib/uhd/utils
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./usrp_burn_mb_eeprom --args=<optional device args> --values="gpsdo=internal"
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-- restore original setting --
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./usrp_burn_mb_eeprom --args=<optional device args> --values="gpsdo=none"
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------------------------------------------------------------------------
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Using the GPSDO in Your Application
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------------------------------------------------------------------------
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By default, if a GPSDO is detected at startup, the USRP will be configured
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to use it as a frequency and time reference. The internal VITA timestamp
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will be initialized to the GPS time, and the internal oscillator will be
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phase-locked to the 10 MHz GPSDO reference. If the GPSDO is not locked to
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satellites, the VITA time will not be initialized.
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GPS data is obtained through the **mboard_sensors** interface. To retrieve
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the current GPS time, use the **gps_time** sensor:
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::
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usrp->get_mboard_sensor("gps_time");
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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++, 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 using
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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** or
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another NMEA parser.
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