A collection of tools for amateur radio astronomy observations




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simple_ra


A collection of tools for amateur radio astronomy observations

Marcus Leech, Science Radio Laboratories, Inc

Introduction

A collection of tools, known as simple_ra has been developed as an open-source toolkit in support of small-scale radio astronomy observations, including:


  • Continuum in any of: total-power, differential, or correlation interferometer modes

  • Pulsar monitoring

  • Spectral observations

The simple_ra application is based on the Gnu Radio SDR application framework, and provides a WXGUI graphical user interface, as well as extensive command-line configuration options, and a suite of post-processing tools.

System Requirements

The software can be made to run on single-core and multi-core systems with at least 2GB of memory, and a modern x86-class CPU running at 2.1GHz or faster.

The software can be installed on both Fedora and Ubuntu systems as well as Scientific Linux 6.3. There is an installer script that will be described later in this document.

SDR hardware is required that is compatible with the gr-osmosdr “plug in” for Gnu Radio, such hardware includes:


  • RTLSDR “dongle” devices

  • Ettus Research USRP devices

  • HackRF and BladeRF devices1

  • AirSpy devices, when they become available

For purposes of time synchronization, it is recommended that the system be configured to use NTP to synchronize the system time. Other services may also be used, they key thing is that the system time should be reasonably accurate at all times so that LMST time-stamps are accurate.

During installation, the system needs to be connected to the Internet, to allow software packages to be downloaded and installed.

The data-logging process produces several megabytes per day of log files, depending on configuration.

Installation

There is an installation script at:

http://www.sbrac.org/files/install-gr-ratools

This script will install the Gnu Radio prerequisites, as well as simple_ra, and related tools.

It should run on recent Fedora, Ubuntu, RedHat, and SL6 distributions.

Once it has been downloaded, it can be run as a shell script:

chmod 755 install-gr-ratools

./install-gr-ratools



The simple_ra command

The command that is used to start the simple_ra application is called simple_ra . Assuming that you've placed your $HOME/bin directory into your command search path, you can start up the application by simply typing simple_ra at the command prompt.



The simple_ra command takes a plethora of command-line parameters, as shown below:

--srate rate

This sets the sample-rate that will be used by the hardware for the device(s) attached to the application to rate, in Hz.

--devid device

This sets the device ID of the main channel to device. See DEVICE NAMING below for more details.

--devid2 device

This sets the device ID of the secondary channel to device. See DEVICE NAMING below for more details. If a real hardware device is specified, then the application automatically enables either differential mode (where the –devid2 channel is a terminated reference), or interferometer mode, depending on the setting of –interf.

--longitude decimal-longitude

This sets the longitude used by the LMST computations to decimal-longitude. Longitudes that are notionally “west” are expressed as negative numbers.

--fftsize size

This sets the size of the FFT used in spectral logging to size. The size of the instantaneous spectral display, however, is always 2048. This setting should, for efficiency reasons, use a size that is a power of 2, and 1024 is probably the smallest useful size.

--freq frequency

This sets the operating, tuned, frequency, in Hz, to frequency. Exponential notation is allowed. So that for example, 1GHz can be entered as 1.0e9.

--gain gain

Set the hardware RF gain to gain. Like –srate and –frequency, this applies to both devices if two devices are used.

--dbw detector-bandwidth

This sets the detector bandwidth, in Hz, to detector-bandwidth. This setting must be less than the sample rate, and is often set to about 80% of the notional sample rate. It can also be used for spectral shaping to a certain degree in RFI situations.

--dcg dc-gain

This sets the DC gain to dc-gain. The value provided must be one of [100,1000,10000,100000].

--lrate logging-rate

This sets the logging interval, in seconds for logged data, to logging-rate. A value of 5 is typical.

--ppm ppm-estimate

For some types of hardware, this can be used to tell the drivers what the estimated parts-per-million frequency offset is. The given ppm-estimate value is a floating-point number.

--fifo fifoname

This sets the filename used to send high-speed detector data to an external FIFO for other types of real-time processing. Normally, this is set to /dev/null, but it can be set to any legitimate file using fifoname. Typically, some external script would set up a FIFO, and the FIFO reader, and then tell simple_ra what the name of this FIFO is.

--skoffs sky-offset

This option is used when the tuned frequency and sky frequency are different. For example, for a standard commercial C-band feed, the tuned frequency range would be 950-1450 MHz, typically, but the sky frequency is 2750Mhz higher. If this is the case, use sky-offset to configure for the use of a down-converter before the receiver hardware. This affects the frequency that is logged in logfiles, as well as de-dispersion calculations for pulsar monitoring.

--expname experiment-name

The software produces two formats of logging files, one of which is in a .CSV format for use with programs like Excel. The experiment-name parameter is used to add a suffix to the .CSV files giving the (abbreviated) experiment name.

--cdevn calib-device-name

This sets the device name to calib-device-name (typically a USB serial device like /dev/ttyUSB0 or /dev/ttyACM0) used to control the calibration on/off signals, if they are used.

--cdevrate calib-device-baud

This sets the hardware baud rate of the calibrator-control device to calib-device-baud. For a USB based serial device, this setting is often not meaningful, but should be specified anyway.

--cdevon calib-device-onstring

This sets the character-string to send to the calibrator-control device to calib-device-onstring for turning the calibrator source ON.

--cdevoff calib-device-offstring

This sets the character-string to send to the calibrator-control device to calib-device-offstring for turning the calibrator source OFF.

--cdevinit calib-device-initstring

This sets the initialization string for the calibrator-control device to calib-device-initstring. This is typically used at startup time to initialize the calibration-control device to a known state.

--cinterval auto-calib-interval

This sets the interval for automatic calibration run to auto-calib-interval, in seconds.

--contime auto-calib-ontime

This sets the ON time for automatic calibration to auto-calib-ontime, in seconds.

--sppe


This enables advanced spectral processing, including notch filters, spectral-flattening, and de-dispersion.

--spde


This enables meaningful spectral display. Without this, there is still a spectral display, but it runs at a very low rate, to conserve CPU cycles.

--sple


This enables spectral logging.

--dfd


This flag is used to disable the detector pre-filter (set with –dbw above). Setting this option reduces the CPU footprint a small amount.

--tpld


This flag is used to disable total-power (or differential or interferometer) detector logging.

--interf


This flag enables a correlation-interferometer mode where the two devices (--devid1 and –devid2) correspond to two coherent hardware channels, and the output is derived using a cross-multiply between the two channels, subject to configurable delays and phase adjustment. This obviously requires hardware that is coherent, and can deliver samples that are time-aligned.

--ppe


This flag controls the initial state of the pulsar processing. By default, pulsar processing is turned OFF.

--which fileprefix

This sets the file prefix to fileprefix for purposes of logging and other functions. Normally, simple_ra places log files in $HOME/simple_ra_data/.... But if fileprefix is specified, data files are instead placed in $HOME/simple_ra_data/fileprefix/....

DEVICE NAMING

The --devid parameter accepts a device name in the format used by the gr-osmodr

"generic" source block, which supports a number of device types, including:



  • Ettus Research UHD/USRP devices

  • RTLSDR dongles

  • HackRF

  • BladeRF


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