Digital Signal Processing in Radio Astronomy

Interferometry

Thu, 03 Aug 2023 00:00:00 +0000

Basic theory of interferometry - Basic theory describing additive and multipicative interferometry.
Using 2-Horn Interferometer for Additive Interferometry - Explanation of how to interpret additive interferometry results, with an example.

Installing gr-radio_astro on Ubuntu 20.04

Tue, 27 Jun 2023 00:00:00 +0000

This will install the spectrometer program spectrometer_w_cal.grc as well as other useful radio astronomy GNURadio programs onto a system using Ubuntu 20.04.

Complete the following steps:

Open a terminal window in Ubuntu.

Install gnuradio external python dependencies and SDR drivers by typing the following and hit enter:

sudo apt install gnuradio gr-osmosdr airspy python3-h5py python3-ephem git cmake liborc-0.4-dev -y

To clone the repository: in the terminal, type and Enter: git clone https://github.com/WVURAIL/gr-radio_astro.git
Switch to the gr-radio_astro directory: cd gr-radio_astro
Switch to the gr-radio_astro 3.8 branch by typing: git checkout gr38
Make a build directory: mkdir build, and then move to it: cd build
Then run the following in the build directory:
```
cmake ..
sudo make
sudo make install
```
Additional Steps for setting the proper Python environment:
Open a terminal window.
Make sure you are at the home directory (type and Enter cd ). Then type gedit .bashrc to open the .bashrc file in an editor.
Scroll to the very bottom of this file, add a blank line, and then copy and paste the following code: export PYTHONPATH=/usr/local/lib/python3/dist-packages:/usr/local/lib/python3.8/dist-packages:$PYTHONPATH
Save and close (x in upper right corner).
Additionally you can create appropriate symbolic links
1. Check which python is the installed version of GNURadio by opening gnuradio-companion in a terminal window and click on Help --> About and noting the python version on the dialog box that opens.
2. Go to the following by typing: cd /usr/local/lib/python3.8/dist-packages or cd /usr/local/lib/python3.9/dist-packages for the appropriate python version.
3. Type ln -s /usr/local/lib/python3/dist-packages/radio_astro

Check that the Installation was Successful

Restart your terminal window. Run the program in Gnuradio:
- In a terminal window type gnuradio-companion
- Open the spectrometer_w_cal.grc program as follows:
  
  File --> Open --> gr-radio_astros --> examples --> *spectrometer_w_cal.grc*
- Plug an Airspy radio, with the LNA attached, into the USB port. Run the program by hitting the start triangle (“execute the flowgraph”) on the menu bar at top. If no errors occur, you are all set!

How to Update files from the gr-radio_astro gr38 Repository

Open the terminal window.
From your home directory (cd ), go to the gr-radio_astro folder: cd gr-radio_astro
Type git status. Check the “On branch …” statement at the top. You want to be in the gr38 branch. To get there, type git checkout gr38.
If a warning message shows up about local changes made that could overwrite files, type git stash.
Type git status to check that you are “On branch gr38”.
Type git pull.
- If a warning message shows up about local changes made that could overwrite files, type git stash.
- Then type git pull again.
Change to the build directory: cd build
Type rm -rf *. NOTE: Make sure you are in the build directory before typing rm -rf *!
Then run the following:
```
cmake ..
sudo make
sudo make install
```
The update is complete.

To Run the __spectrometer_w_cal.grc__ program in Gnuradio After Updating:

In a terminal window type gnuradio-companion.
Close any previous version of spectrometer_w_cal.grc that might be open in Gnuradio.
Open the new version of spectrometer_w_cal.grc from the folder /gr-radio_astro/examples/
- under File select Open;
- Navigate to the gr-radio_astro folder.
- Under examples open DSPIRA; then select spectrometer_w_cal.grc.
Connect an Airspy SDR to a USB port, and start the program running (Hit the black triangle at the top middle ribbon bar.)

Installing Ubuntu

Tue, 27 Jun 2023 00:00:00 +0000

Our software works under Ubuntu versions 22.04 LTS and older.

Installing the Ubuntu OS on a Windows computer will require you to partition the hard drive, copy Ubuntu OS onto a bootable flashdrive, and install it onto the partition, as follows:

A. Partition a Hard Drive - Before installing Ubuntu on the hard disk, you need to partition the hard disk in Windows.

NOTE: A hard drive with at least 250 GB is recommended.

Before proceeding, check that Device Encryption is OFF. (This is also known as Bitlocker.) For most Windows systems, this can be done as follows:

Boot up the computer in Windows.
Open the Start menu.
- In the search box type “encryption”.
- In the menu that pops up, click on Manage Bitlocker.
- Verify that it is off and turn off if needed.
- If it was on and you turn it off, you will need to wait until Windows has completed un-encrypting the hard drive before you can proceed. This could take some time.

Now you are ready to partition the hard drive.

Open a Command Prompt window with admin rights, as follows:
- In the search field, type Command Prompt, or just CMD.
- Click on Run as Administrator from the selections on the right side of the window that pops up.
- Click Yes on the pop-up to allow the app to make changes to your device.
In the Command Prompt window that pops up, enter the command diskmgmt.msc to open the Disk Management utility.
In the Disk Management window, right click on OS (C:) and select the Shrink Volume option in order to reduce the partition size.
Wait for the system to query partition size data; then enter the desired amount of space you want to shrink, and hit in the Shrink button. The amount chosen to shrink will be the amount that will be allotted to Ubuntu. This should be an absolute minimum of 50 GB; we recommend at least 100 GB.

After the shrink process completes, a new unallocated space will be present in your drive. We’ll use this free space to install Ubuntu alongside Windows, as described below.

B. Download Ubuntu 22.04 onto a Bootable Flashdrive

You need to download Ubuntu Desktop 22.04 ISO onto the hard drive in Windows. You want to choose the Desktop version. It will take some time to download this file.
Download BalenaEtcher for Windows and install it if you don’t already have it.
Install a 32 GB or larger flash drive in the usb port.
Run BalenaEtcher. Choose the Ubuntu 22.04.iso file as the image and the flash drive as the target. It will take some time for this to run.

C. Install Ubuntu 22.04 Alongside Windows

Turn off the computer. Place the bootable flash drive in the USB port. Turn on the computer, holding down the bootable key (F12) in order to boot from the Ubuntu USB bootable image.
On the first installation screen, select Install Ubuntu and hit Enter to start the installation process. Complete the prompts as needed.
After the installation is complete, you will restart the computer. Choose the Ubuntu option from the menu that appears.
Check the date and time displayed on your computer. If it is not correct, it must be corrected in order for the installation to be completed successfully. This can be changed in the Date & Time menu under Settings.
Open a Terminal window. This can be found in the Show Applications waffle in the lower left corner of the screen.

NOTE: Most of the commands we use are entered in a Terminal window. We recommend adding the Terminal to your Favorites to be accessed easily.
With the time being correct, in a Terminal window type and enter sudo apt update. Then type and enter sudo apt upgrade. This will bring the Ubuntu installation up to date.

The Ubuntu OS is now ready to use.

Setting Up a 2 Horn Interferometer

Mon, 11 Jul 2022 00:00:00 +0000

Procedure for Setting Up a 2 Horn Interferometer

These are instructions for how to set up and run a 2 horn interferometer using a Lime SDR with GNURadio. The GNURadio spectrometer programs write time-stamped data files once every integration time. For the adding spectrometer, called Interferometer_SimpleSpectrometer_Adding.grc, the data includes horn A spectra, horn B spectra, and the power spectra from the sum of their signals. For the multiplying spectrometer, called Interferometer_SimpleSpectrometer_Multiplying.grc, the data includes horn A spectra, horn B spectra, the magnitude of the interference, and the phase of the interference.

List of Equipment

a. 2 Horn telescopes, each consisting of:

  ▪ horn & can antennae
  ▪ cradle
  ▪ stand
  ▪ bolts for cradle axle
  ▪ clamps - recommended to secure the cradle position after the horn is aligned   b. Electronics

  ▪ computer with the GNURadio spectrometer program on it:
      - adding spectrometer program:  [Interferometer_SimpleSpectrometer_Adding.grc](https://github.com/WVURAIL/dspira-lessons/blob/master/FilesUploaded/interferometer_simpleSpectrometer_Lime_adding.grc)
      - multiplying spectrometer program: [Interferometer_SimpleSpectrometer_Multiplying.grc](https://github.com/WVURAIL/dspira-lessons/blob/master/FilesUploaded/interferometer_simpleSpectrometer_Lime_multiplying.grc)
  ▪ Lime SDR with USB cable to connect to a computer – This SDR can digitize 2 channels.
  ▪ 2 bias T's for powering the LNA's; the Lime does not provide power to the LNA’s.
  ▪ 5 V transformer to power the bias T's
  ▪ 2 SMA cables to connect the Lime Rx outputs to the "RF" inputs of the bias T's
  ▪ 2 long SMA cables to connect the "RF+dc" outputs of the bias T's to the LNA's
  ▪ 2 LNA's

c. Accessories for setting up

  ▪ duct tape - recommended for taping the devices and cables in place
  ▪ inclinometer - recommended for setting the telescope angle
  ▪ E-W (N-S) line - critical!
      - best method: determined, prior to a run, from the shadow of a vertical pole or string at sun's transit
      - or determine using an accurate compass
  ▪ Large protractor to help orient the telescopes
  ▪ pliers for tightening the horn rotation axis
  ▪ string - can be useful for aiding the alignment of the horns relative to each other
  ▪ tape measure
  ▪ tent in case of rain

Schematic Diagram and photo of the electrical connections
Setting up the horns

a. Assemble 2 horns as would be done for a single horn observation. b. For horns with a baseline along the east-west direction, set them parallel to each other, pointing at the same spot in the sky (e.g. the sun when it transits). c. Here are some tips: ▪ Sometime before doing interferometry, establish the N-S direction marking the shadow of a vertical pole when the sun transits. ▪ If the horns are to be set up with an E-W baseline, use some sort of large compass or -square to mark the E-W direction perpendicular to the N-S direction. A tape measure or string can be useful for doing this.
Setting up the electrical connections - REFER TO THE PHOTO ABOVE

a. Data for “Horn A” is collected on the cable that is plugged in to RX1 on the Lime SDR; RX2 is for Horn B. b. Be sure that the 5 V dc transformer for powering the bias-T’s is plugged in, and check that the power strip is on. c. The “RF” terminal of each bias-T is connected to the respective RX1 and RX2 on the Lime. d. The “RF + dc” terminal of each bias-T is connected to the respective LNA.
NOTE ABOUT COMPUTER POWER: Be sure the computer power settings are such that it does not go to sleep. Also, for longer runs it is recommended to have the computer plugged in during the run.

For Adding Interferometry:

a. Run the spectrometer program Interferometer_SimpleSpectrometer_Adding.grc

b. Plug the Lime SDR into a USB port.

c. On the computer set up the file directories for data collection:

  ▪ Create a folder appropriately titled for the data collection, e.g. "Sun_scan_July21". Be sure any folders and filenames have no spaces in them.

  ▪ Run GNURadio: $ gnuradio-companion

  ▪ On the canvas in the Interferometer_SimpleSpectrometer_Adding.grc program, open the Variable boxes described below; these are in the upper left side of the GNURadio canvas:

      • Open the "prefix_hornA" Variable block (double-click it). For "Value" type the pathname to the subfolder that will be used to collect the spectrum of Horn A. This must be in quotes. In the example below horn A data is written to the sub-folder "magnitude_july21" that is in the subfolder "sun_july21" which is a subfolder of "interferometer_data", etc. This will be written in the prefix-hornA Variable box as: "/home/john/dspira_2021/interferometer_data/sun_july21/hornA_july21/"

      • Set up similar file pathnames in the Variable blocks "prefix_hornB" and "prefix_adding".

      • Be sure these sub-folders on the computer have been created.

d. If all is good, you are ready to go. Delete the test files in each folder (not required but recommended).

e. Start the program. Select “Long Integration” and “Writing to File”. If all is good, the graphs should show signals being collected.

For Multiplying Interferometry:

a. Run the spectrometer program Interferometer_SimpleSpectrometer_Multiplying.grc

b. Plug the Lime SDR into a USB port.

c. On the computer set up the file directories for data collection:

  ▪ Create a folder appropriately titled for the data collection, e.g. "Sun_scan_July21". Be sure any folders and filenames have no spaces in them.

  ▪ Run GNURadio: $ gnuradio-companion

  ▪ On the canvas in the Interferometer_SimpleSpectrometer_Multiplying.grc program, open the Variable boxes described below; these are in the upper left side of the GNURadio canvas:

      • Open the "prefix_mag" Variable block (double-click it). For "Value" type the pathname to the subfolder that will be used to collect the spectrum of Horn A. This must be in quotes. In the example below interference magnitude data is written to the sub-folder "magnitude_july21" that is in the subfolder "sun_july21" which is a subfolder of "interferometer_data", etc. This will be written in the prefix-mag Variable box as: "/home/john/dspira_2021/interferometer_data/sun_july21/magnitude_july21/"

      • Set up similar file pathnames in the Variable blocks "prefix_phase", "prefix_hornA", and "prefix_hornB". 

      • Be sure these sub-folders on the computer have been created.

d. If all is good, you are ready to go. Delete the test files in each folder (not required but recommended).

e. Start the program. Select “Long Integration” and “Writing to File”. If all is good, the graphs should show signals being collected.

PlutoSDR software Installation

Wed, 04 Aug 2021 00:00:00 +0000

The steps below outline the installation of software that is needed to run the Pluto SDR in GNURadio. More information and support about GNU Radio and IIO Devices can be found at: https://wiki.analog.com/resources/tools-software/linux-software/gnuradio

Step 1: Install Dependencies

Open a terminal window. Then type (or copy and paste) and enter the following:

sudo apt install libxml2 libxml2-dev bison flex cmake git libaio-dev libboost-all-dev
sudo apt install libusb-1.0-0-dev
sudo apt install libavahi-common-dev libavahi-client-dev
git clone https://github.com/analogdevicesinc/libiio.git
cd libiio
cmake .
make
sudo make install
cd ..

Download and build libad9361-iio

git clone https://github.com/analogdevicesinc/libad9361-iio.git
cd libad9361-iio
cmake .
make
sudo make install
cd ..

Additional Installations

sudo apt install bison flex cmake git libgmp-dev
sudo apt install liborc-dev

Build and install gr-iio from source:

git clone -b upgrade-3.8 https://github.com/analogdevicesinc/gr-iio.git
cd gr-iio
cmake .
make
sudo make install
cd ..
sudo ldconfig

Your system should now be ready to install the PlutoSDR Source block in GNURadio. If there are any problems, refer to the information at: https://wiki.analog.com/resources/tools-software/linux-software/gnuradio

Other Horn Designs

Thu, 29 Jul 2021 00:00:00 +0000

Baby DSPIRA Horn - A smaller version of the design presented above can be found in a pdf here and in videos here. This includes a cradle and stand as part of its construction. This design operates using all of the other components and software used with the standard DSPIRA horn described within this webpage. It provides easy use and is good for demonstrations.
Radio Telescope Base Construction Guide - Instructions for building a radio horn telescope similar in design to the DSPIRA horn.
Cone Horn Construction - Instructions for building a cylindrical radio horn with a cylindrical can.

Build a Simple Spectrometer

Sun, 04 Jul 2021 00:00:00 +0000

Introductory Lessons on Using GNURadio and Some Basic DSP
- Lesson 1 - Introduction to GNURadio basics.
- Lesson 2 - Learning more GNURadio tools building a multiple waveform source.
- Lesson 3 - Demonstration of Fourier series.
- Lesson 4 - Demonstration of how an FFT block works.
- Lesson 5 - Filter basics.
Build a Simple Spectrometer - Directions on building a simple spectrometer for a horn telescope, with detailed explanations of the blocks.

Raspberry Pi

Thu, 01 Jul 2021 00:00:00 +0000

Raspberry Pi’s are inexpensive and the more modern Pi’s are powerful enough to keep up with the level of signal processing on GNURadio associated with Radio Astronomy applications.

Supported Raspberry Pi Devices
Installing Ubuntu image with radio astronomy preinstalled on a Raspberry Pi
Operating system requirement
Installing Ubuntu on Raspberry Pi
- Prerequisites
Post Installation actions:
- Interacting with the Raspberry Pi
Installing gr-radio_astro

Supported Raspberry Pi Devices

All devices must have RAM greater than 4GB

Raspberry Pi 4 Model B
Raspberry Pi 400

Installing Ubuntu image with radio astronomy preinstalled on a Raspberry Pi

This image requires a minimum of 16GB of space on the SD card.

Download the image here
Unzip the .zip file.
Use Raspberry Pi Imager to install this image.
1. Insert SD card into your card reader on your computer
2. Open Raspberry Pi imager.
3. Click Choose OS, and choose Use Custom.
4. Select the correct image file downloaded in step 1 and 2 from your system.
5. Click Choose storage and select your inserted SD card.
6. Click write.
7. More info here and a video
Insert SD card to Raspberry Pi and power it up.
The default user name is pi, with password raspberry. Change the password after first boot.

Setting OS and installing software from scratch.

Operating system requirement

Ubuntu for Raspberry Pi Click here for more Info

Note: The custom gr-radio_astro software is now only supported for GNURadio 3.8 only. The Raspberry Pi OS by default installs GNURadio 3.7 which is not longer supported.

Installing Ubuntu on Raspberry Pi

Prerequisites

Support Raspberry Pi
A microSD card (9GB minimum, 16GB recommended)
A computer with a microSD card drive
A micro USB-C power cable
A monitor with an HDMI interface (Optionally for installing Ubuntu Server)
A micro HDMI cable (Optionally for installing Ubuntu Server)
A USB keyboard and mouse (Optionally for installing Ubuntu Server)

Instructions from Ubuntu to install the OS on the Raspberry Pi 4

NOTE: Firstly, for Ubuntu desktop a monitor and mouse and keyboard is required. If you do not want to access the full desktop interface of ubuntu and only interact via command line interface you can install Ubuntu Server instruction for Ubuntu server installation here. Secondly, Raspberry Pi is built on an ARM based architecture any version of Ubuntu will not work. The OS has to specific to the Pi.

Post OS Installation actions:

Interacting with the Raspberry Pi

Using a moniter and mouse and keyboard like any other desktop.
Using SSH:
1. This method can be used on any machine with ssh server enabled.
2. Install X server on your computer. VcXcrv on windows and XQuartz for macOS.
3. Power up the Raspberry Pi and connect your computer via ethernet cable
4. First we need to determine the IP address of the raspberry PI: How to determine Raspberry PI IP address
5. If the determined IP address is <IP address> then in the terminal type ssh -Y pi@<IP address>
6. More info on SSH here
Using PuTTy on Windows:
1. Download PuTTy.
2. Add IP address in the hostname field.
Using VNC: More info here

Installing `gr-radio_astro`: Installing gr-radio_astro

Notes: run volk_profile after installing everything to make sure GNURadio is optimized to work on your device.

Installing gr-radio_astro

Thu, 01 Jul 2021 00:00:00 +0000

This will install the spectrometer program spectrometer_w_cal.grc as well as other useful radio astronomy GNURadio programs from the gr_radio_astro repository in GitHub.

NOTE: The instructions on this page will install files for Ubuntu 22.04. If you are using Ubuntu 20.04 LTS, click here for the installation.

Complete the following steps:

Open a Terminal window. This can be found in the Show Applications waffle in the lower left corner of the screen.

NOTE: Most of the commands we use are entered in a Terminal window. We recommend adding the Terminal to your Favorites to be accessed easily.
If you have not already done so during the GNURadio installation, install the gnuradio external python dependencies and SDR drivers by typing the following and hit enter:

sudo apt install gnuradio gr-osmosdr airspy python3-h5py python3-ephem git cmake liborc-0.4-dev -y
In the terminal type and enter:

git clone https://github.com/WVURAIL/gr-radio_astro.git
Switch to the gr-radio_astro directory: cd gr-radio_astro
Type and enter: git branch to verify that you are on the “main” branch. If you are NOT on the main branch, then type and enter: git checkout main.
Make a build directory: mkdir build, and then move to it: cd build
Then run the following in the build directory:
```
cmake ..
make
sudo make install
```
To check that the installation was successful, type and enter cd to get to the home directory. Run the program in Gnuradio:
- In a terminal window type gnuradio-companion
- Open the spectrometer_w_cal.grc program as follows from the File menu:
  
  File –> Open –> gr-radio_astros –> examples –> DSPIRA –> spectrometer_w_cal.grc
- Plug an Airspy radio, with the LNA attached, into the USB port. Run the program by hitting the start triangle (“execute the flowgraph”) on the menu bar at top. If no errors occur, you are all set!

Occasionally the files in gr_radio_astro may change. Complete the following to update these files.

How to Update files from the gr-radio_astro Repository

Open the terminal window.
From your home directory (cd ), go to the gr-radio_astro folder: cd gr-radio_astro
Type git status. Check the “On branch …” statement at the top. You want to be in the “main” branch. To get there, type git checkout main.
Type git pull.
- If a warning message shows up about local changes made that could overwrite files, type git stash.
- Then type git pull again.
Change to the build directory: cd build
Type rm -rf *. NOTE: Make sure you are in the build directory before typing rm -rf *!
Then run the following:
```
cmake ..
make
sudo make install
```
The update is complete.

To Run the __spectrometer_w_cal.grc__ program in Gnuradio After Updating:

In a terminal window type gnuradio-companion.
Close any previous version of spectrometer_w_cal.grc that might be open in Gnuradio.
Open the new version of spectrometer_w_cal.grc from the folder /gr-radio_astro/examples/DSPIRA/
- under File select Open;
- Navigate to the gr-radio_astro folder.
- Under examples open DSPIRA; then select spectrometer_w_cal.grc.
Connect an Airspy SDR to a USB port, and start the program running (Hit the black triangle at the top middle ribbon bar.)

Installing GNURadio

Thu, 01 Jul 2021 00:00:00 +0000

To install GNURadio, complete the following:

Open a terminal window.
Type and enter sudo apt update
Type and enter sudo apt upgrade
Type and enter

sudo apt install gnuradio gr-osmosdr airspy python3-h5py python3-ephem git cmake liborc-0.4-dev -y.

You may need to respond ‘Y’ to a few prompts before installation is complete.

Digital Signal Processing in Radio Astronomy

Interferometry

Installing gr-radio_astro on Ubuntu 20.04

How to Update files from the gr-radio_astro gr38 Repository

Installing Ubuntu

Setting Up a 2 Horn Interferometer

Procedure for Setting Up a 2 Horn Interferometer

PlutoSDR software Installation

Other Horn Designs

Build a Simple Spectrometer

Raspberry Pi

Supported Raspberry Pi Devices

Installing Ubuntu image with radio astronomy preinstalled on a Raspberry Pi

Setting OS and installing software from scratch.

Operating system requirement

Installing Ubuntu on Raspberry Pi

Prerequisites

Post OS Installation actions:

Interacting with the Raspberry Pi

Installing gr-radio_astro: Installing gr-radio_astro

Installing gr-radio_astro

How to Update files from the gr-radio_astro Repository

Installing GNURadio

Installing `gr-radio_astro`: Installing gr-radio_astro