Download SystemManual - NRAO Safe Server

System Manual
Wideband Artificial Pulsar Signal Simulator
Rev A
April 29, 2015
Group Members:
Alexander Botten
Kerlin Canelli
Sponsor:
Randy McCullough, Lead Engineer - Digital Group, Green Bank
Instructor:
Yenumula Reddy
Abstract
This document is the culmination of the first year of work on the Wideband Artificial Pulsar
Signal Simulation Device. All research conducted and work done are outlined on the following pages.
The Wideband Artificial Pulsar Signal Simulation Device (referred to as WBAP) is a device
designed by senior students at WVU for the NRAO at Green Bank, WV. This device will be used to test
the analytic backend at Green Bank in an attempt to verify the function of recent updates.
Table of Contents
Abstract ......................................................................................................................................................2
Introduction ................................................................................................................................................4
Extended Problem Statement ..................................................................................................................4
Background ..........................................................................................................................................4
Objective ..............................................................................................................................................5
Design Achievements .................................................................................................................................6
Hardware Design........................................................................................................................................7
Eagle PCB Layout .....................................................................................................................................7
Materials....................................................................................................................................................8
Reflections .................................................................................................................................................9
Appendix I – Block Diagrams .................................................................................................................10
Appendix II – Original Design Proposal..................................................................................................14
Appendix III – Summary of Changes ......................................................................................................45
Introduction
Our project is to design a wide-band artificial pulsar signal simulation device for the
NRAO at Green Bank, WV. This paper details the project to its full extent. We have covered
the problem statement, requirement specifications, system design, test plans, and a project
management plan. We have also included our individual research papers in the appendix of
this paper. This paper will serve as the guideline going forward into the building of our device.
Extended Problem Statement
Background
At the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, it
has one of the largest astronomical telescopes in the world.
This radio astronomy
observatory has an active engineering research and development program covering a wide
field of different disciplines including the study and research of pulsars. A pulsar is simple
rotating neutron star that emits a beam of electromagnetic radiation. This pulsar can only be
seen when it is point in the direction of the earth.
At the NRAO they have done extensive research in the study of pulsars. Over the
years they have develop sophisticated digital backends in support of pulsar research and
pulsar timing projects. One of these backends that the NRAO at Green Bank is currently
using is called GUPPI which stands for Green Bank Ultimate Pulsar Processing Instrument.
This is a flexible signal processor that uses field programmable gate hardware and design
tools for pulsar observation. Another digital backend that the NRAO is about put in place is
called VEGAS which stands for the Versatile Green Bank Astronomical Spectrometer. This
contains eight independent spectrometers and provides up to 64 spectral windows and wide
bandwidths which can be used to measure the properties of light from a pulsar.
Objective
With these digital backends being developed and used at the observatory it is
important that they are operating correctly when observing a pulsar. To test this backends the
solution would be to develop an artificial pulsar that would be able to closely approximate the
natural characteristics of an actual pulsar. This means to reproduce the pulsar period and the
pulsar pulse dispersion through the interstellar medium. At Green Bank they have develop an
artificial pulsar though it does not have the capabilities to test some of the mechanisms with
these new digital backends. With the production of this test instrument, it will assist in selfsufficient testing of these backends which will remove some dependence from use the
telescope and facility infrastructure availability. Also with the creation of this instrument, it will
hopefully advance the development of pulsar research and allow a better understanding of
how pulsars function.
Design Achievements
 Block Diagram – REV 3
The block diagram has been updated to better reflect the final design of the project. The block diagram
and the Eagle schematic are very similar, with the block diagram being easier to follow and understand.
 Component Selection
All of the components needed for the currently designed WBAP have been selected. All selected
components meet the requirements of the project. Components have been verified to work as designed.
 Eagle PCB Schematic – REV A
The first version of the WBAP Eagle schematic is complete. All connections have been made, all
components have been designed and added to the Eagle Library, and vias have been added to
components where necessary. The current schematic is production ready, though more tweaks to the
design may be required.
Hardware Design
Eagle PCB Layout
Above is a capture of the Eagle PCB schematic as it currently stands. The schematic includes
every component (including the control card). All components have the required connections for
operation. All components have appropriate values assigned to them.
The red connections on the right half of the board represent the RF connections. The RF
channels are thicker than the normal connections; this is a result of material-based calculations
performed with the intent of impedance matching to the transmission lines that will be used alongside
the board. The RF channels, as currently designed, avoid any sudden changes in direction in an attempt
to minimize flux leakage from the lines. Symmetry was a desired attribute for the RF traces to
guarantee that both lines were subject to the same stresses and variables;however, due to the current
design, symmetry was only achieved to a certain extent.
The blue channels represent the data connections from the control card. As the coding for the
control of the switches still needs to be done, the data connections have been left out. This allows for
the future developers to select which data bits to use when controlling the switches.
The red connections in the top left of the card represent the +15VDC connections. There is no
plane for the +15VDC voltage, so a single trace on the top layer was used. This may be changed in
future revisions if necessary, but works in its current form.
Materials
The following materials were used in the creation of the WBAP. Datasheets (where
available) for the following components can be found on the Redmine website.

Noisecom NC2501 (x2)
◦ RF noise source.
◦ Uses +15VDC to create RF noise ranging from 1-1000MHz.
◦ Two noise sources were used in our current design. One noise source creates
the noise floor that represents the interference from the interstellar medium.
The second noise source is used to create the pulsar's signal.

MAXIM MAX2064 VGA
◦ Dual-Channel Variable Gain Amplifier
◦ Range: 50-1000MHz
◦ High-Linearity
◦ Controlled using SPI interface from control card

NetBurner MOD5270
◦ Single-Board Computer
◦ Used as control card for WBAP daughter card
◦ Synced to site-wide 10MHz clock by removing built-in crystal oscillator

Hittite HMC241QS16 (x4)
◦ 2-bit controlled, 4 input RF switch
◦ Two used per RF line to provide isolation during filtering. This prevents
signal from bouncing-back through an inactive filter.

RS-232 Cable
◦ Standard serial communication transmission line

RJ-45 Cable
◦ Ethernet cable for use in interfacing with control card

LMS Filters (x6)
◦ RF Low-pass Filters
◦ Multiple filters with varying cut-off frequencies used.

50 Ohm Coaxial Cable
◦ Transmission line used to carry RF noise from WBAP outputs.
Reflections
This project was very ambitious from the start. The decision to change from a
one- to a two-year project completion date was very helpful. The project could
potentially have been finished in a single year's worth of work, but only if the project
had been the only task. All of the auxiliary papers that didn't directly relate to the project
itself only served to take time away from the work done on the project.
The project also served as a learning experience for everyone involved. Through
the life of the project, it was revealed just what knowledge was missing from the typical
college program. It was also revealed how important communication is when working
between two groups.
Communication played a large part in this project. With the only contact being off
campus, any issues that arose would require additional time to solve. This resulted in
slower work.
For future builders of this project, communication should be paramount. This is a
complex project that will require guidance, and that can only be accomplished by
establishing communication early in the life of the project. This project will also require
the future designers to learn how to use multiple software and hardware involved in
signals and communications.
Appendix I – Block Diagrams
Illustration 1: The original block diagram. This block
diagram depicts the first conception of the WBAP. It is
a rough design that only considers what must be
accomplished in the project, and not necessarily how to
implement these features.
Illus
tration 2: This is the second block diagram. This block diagram is much
more fleshed out than the first, as it includes components that would
achieve the desired features. This block diagram also reflects the decision
to leave the dispersion and phase shift as future implementations.
Illustration 3: This is the final block diagram. This block diagram differs from
the second block diagram in that it shows the fix for isolation by including
switches on both sides of the filters.
Appendix II – Original Design Proposal
Final Design Proposal
December 3, 2014
Group 6: Greenbank Wideband Artificial Pulsar
Group Members:
Alexander Botten
Kerlin Canelli
Sponsor:
Randy McCullough, Lead Engineer - Digital Group, Green Bank
Instructor:
Yenumula Reddy
Contents
Introduction ..................................................................................................................................... 3
Extended Problem Statement .......................................................................................................... 4
Background ................................................................................................................................. 4
Objective ........................................................................................................................................ 5
Requirements Specification ............................................................................................................ 6
Marketing Requirements ................................................................................................................. 8
Overall architecture of the system .................................................................................................. 9
User Interface Specification .......................................................................................................... 10
Software specifications to the function level .................................................................................11
Test Plans ...................................................................................................................................... 13
Project Management Plan ............................................................................................................. 15
Appendix 1 – Project Website ....................................................................................................... 17
Background – Green Bank Telescope ........................................................................................... 20
Background – Pulsars.................................................................................................................... 21
Project Design/Needs .................................................................................................................... 22
Objective Tree ............................................................................................................................... 23
Stakeholders .................................................................................................................................. 25
Conclusion .................................................................................................................................... 26
References ..................................................................................................................................... 27
Introduction
Our project is to design a wide-band artificial pulsar signal simulation device for the
NRAO at Green Bank, WV. This paper details the project to its full extent. We have covered
the problem statement, requirement specifications, system design, test plans, and a project
management plan. We have also included our individual research papers in the appendix of
this paper. This paper will serve as the guideline going forward into the building of our device.
Extended Problem Statement
Background
At the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, it
has one of the largest astronomical telescopes in the world.
This radio astronomy
observatory has an active engineering research and development program covering a wide
field of different disciplines including the study and research of pulsars. A pulsar is simple
rotating neutron star that emits a beam of electromagnetic radiation. This pulsar can only be
seen when it is point in the direction of the earth.
At the NRAO they have done extensive research in the study of pulsars. Over the
years they have develop sophisticated digital backends in support of pulsar research and
pulsar timing projects. One of these backends that the NRAO at Green Bank is currently
using is called GUPPI which stands for Green Bank Ultimate Pulsar Processing Instrument.
This is a flexible signal processor that uses field programmable gate hardware and design
tools for pulsar observation. Another digital backend that the NRAO is about put in place is
called VEGAS which stands for the Versatile Green Bank Astronomical Spectrometer. This
contains eight independent spectrometers and provides up to 64 spectral windows and wide
bandwidths which can be used to measure the properties of light from a pulsar.
Objective
With these digital backends being developed and used at the observatory it is
important that they are operating correctly when observing a pulsar. To test this backends the
solution would be to develop an artificial pulsar that would be able to closely approximate the
natural characteristics of an actual pulsar. This means to reproduce the pulsar period and the
pulsar pulse dispersion through the interstellar medium. At Green Bank they have develop an
artificial pulsar though it does not have the capabilities to test some of the mechanisms with
these new digital backends. With the production of this test instrument, it will assist in selfsufficient testing of these backends which will remove some dependence from use the
telescope and facility infrastructure availability. Also with the creation of this instrument, it will
hopefully advance the development of pulsar research and allow a better understanding of
how pulsars function.
Requirements Specification
Functional Requirements and Engineering Requirements
For an optimal finished product, there are few requirements that need to be meet.
1. Larger Bandwidth – (100MHz-1000MHz)
This is the most important feature that is required for this device. The current
artificial pulsar device is restrained to a much smaller bandwidth. Having a
larger bandwidth will allow a more accurate reproduction of an actual pulsar.
Also this bandwidth should be user selectable. The plan is to implement this by
using noise sources and a tunable bandpass filter.
2. Command Line Interface
This will be a user interface that will be implemented using code. The plan is to
use either C++ or Python coding languages to execute this allowing the
scientists to easily operate the device.
3. Adjustable pulse amplitude
This is to allow the scientists to adjust and differ the pulse to simulate variability
when creating the pulsars.
This will be accomplished by using a voltage
controlled attenuator.
4. User selectable pulse width and period
The voltage controlled attenuator will also be used to accomplish this task.
Along with coding, it will allow the scientists the option to adjust and set the
pulse wide and period of the pulsar they desire.
5. Polarization of pulses
This will be created by using a voltage controlled phase shifter.
This will
represent the variety of different phases a pulsar can be and will scientists to
adjust the phase to see if the outputs are correct with the digital backends.
6. Independent noise floor
In space, there are many other variables that could affect a pulsar when
travelling through the interstellar medium.
To reproduce this effect, and
independent noise floor is to be put into place. Then will be done by using a
second noise source and then combing that to the noise source that is
reproducing the pulsar.
7. Sub pulses and interpulses
This would be a nice added feature for our device.
When studying actual
pulsars, they sometimes create sub pulses, which are pulses that are less
strong emitted by a pulsar, and interpulses, which is a pulse emitted to the
opposite end of the pulsar. With this feature it added to the device, it would
accurately reproduce a real pulsar.
Marketing Requirements
Marketing Requirements are essentially not applicable for this particular project
because there is no real market for this instrument. The NRAO in Green Bank, WV will be the
only primary stakeholders interested in using this device. There is a possibility of marketing to
other radio observatories, though at this stage of development there is no marketable use of
this product.
System Design
Overall architecture of the system
The device we are going to design will be a black-box piece of testing
equipment. For the internals, the following diagram was provided by Randy as a
proposed layout of components. The device will be relatively easy to use. The only
knowledge needed to operate the device would be a simple understanding of a
command-line interface. Once the signal is fed into the analytical backend at Green
Bank, the engineers and scientists on their end will simply need to use their machines
as normal. Our finalized device will essentially be plug-and-play with their system.
User Interface Specification
The user interface will be a text-based interface. It was specifically requested that we
do not use a GUI, but instead try to structure our interface as a command-line style interface.
The user will first be met by a screen prompting them to log in to the device. The first
prompt will ask for the username. Once the username has been entered, and verified as a
valid username, the user will be prompted for a password. Once the password is correctly
entered, the software will bring the user to the main menu.
We will use a text menu that contains options corresponding to setting each individual
value of the simulated pulsar signal. Once an option is selected from the menu, the user will
be prompted to enter the value of the variable they selected. The user will be given a
message confirming that the value was changed to their specification, and then the menu will
be shown again.
The menu will include an option to begin producing the signal with the given
parameters. While the signal is being produced, the user will be shown a prompt to provide
the proper command to stop the signal generation, otherwise the signal will continue to be
produced for as long as the user allows it to run. When the user cancels the production of the
signal, the user will be returned to the main menu. From the main menu, the user can change
the desired values, re-run the simulation, or logout from the simulation software. When the
logout option is selected, the software will sit on the prompt for the username.
As far as physical interface, there will be three physical features. The first feature will
be a power switch. This will be used to turn on and off the device when it is or is not needed.
The second feature will be the Ethernet port. This port is going to be how the user’s computer
interfaces with the artificial pulsar. And finally, the device will have some transmission lines
that will carry the signal that is being generated.
Software specifications to the function level
The first part of our software is the user login interface. Using a prompt to collect input
from the user, we will compare the provided username to a list of usernames that will have
been provided before-hand. Once the username is confirmed, the index of the username will
be used in a secondary matrix to confirm that the correct password will be entered. A failed
attempt will result in a return to the prompt for the username. Once the password check has
been passed with a correct password input, the software will display the main menu.
The main menu will be a list of controllable parameters, a run function, and a logout
function. When each of the controllable parameters is selected, the software will show a
prompt for and get input from the user to set the chosen parameter to an acceptable value. If
the value is not within bounds of an acceptable range, the prompt will show again, and a new
input will be taken from the user. After a valid input, the main menu will show again.
The run function will turn on the power to the signal generator. This function will also
send the value of each variable to the corresponding control component. This is when the
previous inputs will get implemented in the physical attributes of each component. This
function will display a prompt saying that the signal is being generated, and give the proper
action to take to turn off the signal. While the signal is on, the user will not have control of
variable input. Once the signal is turned off, the power to the signal generator will be turned
off, and the main menu will be shown again.
The logout function will wipe the screen and display the username input prompt. This
screen will be the first and last screen the user sees when interacting with the device.
Test Plans
To test our device, we will be using software available through Green Bank. The main
analytical software we will be using is RF/Microwave simulation software. Using the software,
we will be able to finalize our design. This software will have to be used on site, and therefore
will either need to be run by a staff member at Green Bank while we tell the staff member
parameters, or it will require a trip to Green Bank. The later method of testing is preferred, but
as it is more time-intensive and costly, it will not be used for early testing.
Once we have verified that our design works, we will build our device. Testing during
this stage will be difficult, as the device will need to be tested at Green Bank, where we have
access to the needed sensors and scopes. There shouldn’t be any major redesign during the
build stage, as it would be costly and set us back as we wait for parts to be procured. The
majority of our testing will be through the simulation software.
Once the device is finalized, testing to confirm that the device is still functioning
properly will require someone with knowledge of pulsar behavior. Beyond the obvious test of
whether or not you are getting an output at all, the only way to test that the output of the
device is correct would be to configure the device to run similar to a known pulsar and
compare the output from the simulation and the real thing. If the signals do not match, testing
will need to be done on a per-component basis to find the component that is incorrectly
modulating the signal.
To test that the user-interface and software functions are working properly, we can just
run the software without being connected to the device. We would be able to confirm that our
login verification works properly using a matrix filled with dummy information. The variablesetting functions can be tested by adding running them and confirming that the values are
correctly recorded within the software.
Project Management Plan
Up to this point, the entirety of the project has been a collaboration between both
members (aside from stated individual work). Since our group consists of only two people, we
have decided that it would be less efficient to separate work more than is absolutely
necessary. By working together on each aspect of the project, we both have a better grasp of
the overall project. This allows us to complete each individual task in a fashion that results in
a better product. Both members contribute equally to the project.
As for planning ahead and creating a work schedule for the future, we have one
problem that prevents much planning. Our project will require a large amount of simulation
before the building step can begin. The simulation software required for our project is only
available to us through Green Bank. This software is also in high demand among the
employees of Green Bank, so we have to get simulation time where we can. This results in an
inability to accurately predict dates for milestones and “check-points.”
As of right now, we plan to coordinate with Randy on when we can get simulation time.
In the meantime, we will be continuing to further our knowledge on each individual component
of the design, as well as begin to select potential components. One element of the project that
we can work on is the user interface. The user interface should take no more than a month to
complete and test. The only test we won’t be able to perform until later is outputting from the
software to the hardware to ensure correct control.
While we may be limited on what we can do without the simulation software, it allows
us time to adequately document our process and research. This is a key component of the
project so that in the event that we do not complete the device, it would not be difficult for
someone else to pick up from where we left off in the design.
References
"Green Bank Site." National Radio Astronomy Observatory. Web. 22 October 2014.
<https://science.nrao.edu/facilities/gbt/>.
"Pulsar." Merriam-Webster. Merriam-Webster. Web. 22 October 2014. <http://www.merriamwebster.com/dictionary/pulsar>.
McCullough, Randy. “Wideband Artificial Pulsar.” Green Bank/WVU Visit. Green Bank, West
Virginia. 14 October 2014.
Lorimer, D. R., and M. Kramer. Handbook of Pulsar Astronomy. Cambridge, UK: Cambridge
UP, 2005. Print.
Appendix 1 – Project Website
https://redmine.lcseecloud.net/projects/greenbank-wideband-artificial-pulsar-randymccullough
Above is the link to our Redmine page associated with our artificial pulsar project. The
website contains all of our documents throughout the life of the project (through Spring 2015),
discussion threads related to our project, as well as documentation pertaining to work done.
Appendix 2 – Individual Research Papers
Individual Research Paper
October 22nd, 2014
Group 6: Greenbank Wideband Artificial Pulsar
Alexander Botten
Group Members:
Kerlin Canelli
Sponsor:
Randy McCullough, Lead Engineer - Digital Group, Green Bank
Instructor:
Yenumula Reddy
Contents
Background: Green Bank
Telescope…………………………………………………………………………………………………
……3
Background:
Pulsars……………………………………………………………………………………………………
…………………….…..4
Project
Design/Needs……………..………………………………………………………………………………
…………………………….5
Objective
Tree………………………………………………………………………………………………………
……………………………….6
Stakeholders………………………………………………………………………………………………
……………………………………….…7
Conclusion…………….…………………………………………………………………………………
………………………………………….…8
References…………………………………………………………………………………………………
………………………………………….9
Background – Green Bank Telescope
The National Radio Astronomy Observatory (NRAO) in Green Bank, WV operates the world
premiere astronomical telescope operating at meter to millimeter wavelengths. The telescope was
constructed from 1991 – 2002, and had its first light, or first use, on August 22nd, 2000. The telescope is
the world’s largest fully steerable radio telescope, allowing it access to 85% of the entire celestial
sphere. The telescope boasts a 100-meter diameter collecting area, an unblocked aperture, and surface
accuracy that provides unprecedented sensitivity across an operating range of 0.1 – 116 GHz.
The telescope is used for astronomy about 6500 hours every year, with 2000-3000 hours per
year available to high frequency science. The telescope is responsible for many discoveries including
the detection of three new millisecond pulsars in 2002, a large coil-shaped magnetic field in the Orion
molecular cloud, the most massive neutron star known, and complex molecules (such as sugar) in
space. Part of the allure of the telescope is its high efficiency, flexibility, and ease of use. These allow
for the rapid response to new scientific ideas.
Background – Pulsars
A pulsar, or pulsating star, is a highly magnetized, rotating neutron star. The star emits a beam
of electromagnetic radiation that can only be observed when the beam of emission is pointing towards
Earth. The emissions can take the form of radio wavelengths, visible light, X-ray, and/or gamma ray
wavelengths. Pulsars exhibit precise rotational periods ranging from roughly milliseconds to seconds.
Certain types of pulsars rival atomic clocks in their accuracy in keeping time. The precise periods make
pulsars useful tools. Observations of a pulsar in a binary neutron star system (a star system consisting
of two neutron star rotating around their common center of mass) were used to indirectly confirm the
existence of gravitational radiation. The first extrasolar planets were also discovered around a pulsar.
The formation of a pulsar begins when the core of a massive star is compressed during a
supernova. The core collapses into a neutron star, or a highly dense star made predominantly out of
closely packed neutrons. The neutron star has a much smaller radius than the star from which it was
created. The newly created neutron star retains most of its angular momentum. The high angular
momentum and reduced radius result in the neutron star having a very high rotation speed. The high
rotational energy generates an electrical field from the movement of the strong magnetic field. This
electric field causes the acceleration of protons and electrons on the star surface, resulting in a beam of
radiation that is emitted along the magnetic axis of the pulsar. The magnetic axis is not necessarily the
same as the rotational axis. This misalignment causes the beam of radiation to be seen once for every
rotation of the neutron star, not unlike how the beam from a lighthouse can only be seen when it is
directed at you.
Project Design/Needs
The NRAO currently has an artificial pulsar that can be used to test their analytical backend, but
the introduction of a more advanced backend has resulted in the need for a new, more powerful
artificial pulsar. The use of an artificial pulsar to fine-tune the telescope’s analytical backend is much
more reliable and practical than viewing a known pulsar with the telescope, as time on the telescope
itself is highly valuable.
The current artificial pulsar only operates on a bandwidth of about 127 MHz, which isn’t very
useful in the approximation of high-frequency pulsars. It also has no provisions for representing pulse
dispersion and is dependent upon the use of a signal generator for establishing the requisite pulse
period.
The proposed new artificial pulsar will be a “black box.” It will be self-contained and only have
an Ethernet jack (or similar standardized interface) as a means of connection. The new artificial pulsar
is proposed to have the following features (in order from most important – least important):
1. A selectable bandwidth ranging from 100 MHz to 1000 MHz
2. A command-line interface that accepts commands structured similar to
commands written in Python
3. Independent, non-polarized noise floor
4. Adjustable pulse amplitude with pseudo-randomly generated differences in
amplitude from pulse to pulse
5. A selectable pulse width (microsecond – millisecond) and period (millisecond –
second)
6. Selectable polarization of pulses of up to 100%
7. Sub pulses and/or interpulses
Objective Tree
Figure 1: Objective Tree
Stakeholders
Because this device is meant to be used for a single purpose, and is not meant to be sold or
commercialized, the sole stakeholder in the project is the team of scientists and engineers at Green
Bank. This will be a one-off device that is only used for the tuning and testing of the telescope’s
analytical backend. There is not a competing product, nor is there a desire to earn money off of the
device. This results in the only desired outcome to be that the device operates correctly with the desired
specifications. Because the device will be used in tandem with high-end analytical devices, the concern
of cost is outweighed by the necessity of the device also being high-end.
Conclusion
In the spirit of the advancement of scientific knowledge, the Green Bank Telescope has
undergone improvements since its initial construction. As the analytical capabilities of the telescope
have improved, the need for a better artificial pulsar has arisen. The team at Green Bank has proposed
the design of a better artificial pulsar with a list of desired specifications so they have a greater ability
to test their analytical backend without requiring the use of the telescope. The device will be a one-off
scientific tool meant only for use by the Green Bank scientists and engineers, and therefore does not
have a business objective beyond the device’s functionality.
References
"Green Bank Site." National Radio Astronomy Observatory. Web. 22 October 2014.
<https://science.nrao.edu/facilities/gbt/>.
"Pulsar." Merriam-Webster. Merriam-Webster. Web. 22 October 2014. <http://www.merriamwebster.com/dictionary/pulsar>.
McCullough, Randy. “Wideband Artificial Pulsar.” Green Bank/WVU Visit. Green Bank, West
Virginia. 14 October 2014.
Lorimer, D. R., and M. Kramer. Handbook of Pulsar Astronomy. Cambridge, UK: Cambridge UP,
2005. Print.
Background Research Paper
Final
October 22, 2014
Group 6
Wideband Artificial Pulsar
Group Members:
Alexander Botten
Kerlin Canelli
Instructor:
Yenumula V Reddy
Sponsor/Mentor:
Randy McCullough
Contents
Background
3
Needs
4
Stakeholders
5
Objectives
5
Design
7
Implementation
9
Conclusion
9
References
10
Background
Pulsar Background
What is a pulsar? Well let’s start with a neutron star. A neutron star is a stellar
remnant caused after a massive star has a supernova. The star collapses in on itself
but keeps most of its angular momentum. This causes a very high rotation speed and
because neutron stars are so small and dense it causes a beam of electromagnetic
radiation. This beam is a pulsar. They can only be seen by us when pointed in the
direction of Earth. Pulsar and neutrons stars are very important fields to study,
because even though scientists have been studying them for the past 40 years, there
is little known about them. It is important to study pulsars because pulsars are
interesting celestial objects. It is an object propelling radiation into space at close to
the speed of light or an object more massive than our Sun that would easily fit inside a
city. Also by studying pulsars, they aid in learning about the physics of our universe
such as density, gravity, magnetic fields and electric fields.
Green Bank Background
At the National Radio Astronomy Observatory (NRAO) in Green Bank, West
Virginia, it has one of the largest astronomical telescopes in the world. This radio
astronomy observatory has an active engineering research and development program
covering a wide field of different disciplines including the study and research of
pulsars. Over the years they have develop sophisticated digital backends in support of
pulsar research and pulsar timing projects. One of these backends that the NRAO at
Green Bank is currently using is called GUPPI which stands for Green Bank Ultimate
Pulsar Processing Instrument. This is a flexible signal processor that uses field
programmable gate hardware and design tools for pulsar observation. Another digital
backend that the NRAO is about put in place is called VEGAS which stands for the
Versatile Green Bank Astronomical Spectrometer. This contains eight independent
spectrometers and provides up to 64 spectral windows and wide bandwidths which
can be used to measure the properties of light from a pulsar.
Needs
With these digital backends being developed and used at the observatory it is
important that they are operating correctly when observing a pulsar. To test this
backends the solution would be to develop an artificial pulsar that would be able to
closely approximate the natural characteristics of an actual pulsar. This means to
reproduce the pulsar period and the pulsar pulse dispersion through the interstellar
medium. At Green Bank they have develop an artificial pulsar though it does not have
the capabilities to test some of the mechanisms with these new digital backends. With
the production of this test instrument, it will assist in self-sufficient testing of these
backends which will remove some dependence from use the telescope and facility
infrastructure availability. Also with the creation of this instrument, it will hopefully
advance the development of pulsar research and allow a better understanding of how
pulsars function.
Stakeholders
NRAO in Green Bank, WV
The scientists and astronomers at Green Bank, WV are the primary and
only real stakeholders for this device. They are the only group right now that
needs this device to operational. This project idea was given by the NRAO
because of their need to test the digital backends used to study pulsars. The
many of other different radio observatories that may find use for this device but
as of now this primary for the NRAO and not for marketable use.
Objectives
There has been a list of tasks that the scientists from the NRAO have made in
which they would like to see this new artificial pulsar be able to satisfy. The first is a
larger bandwidth. The bandwidth should range from 100MHz-1000MHz. This is the
most important feature that is required for this device. The current artificial pulsar
device is restrained to a much smaller bandwidth. Having a larger bandwidth will allow
a more accurate reproduction of an actual pulsar. Also this bandwidth should be user
selectable.
The second is a command line interface. This will be a user interface that will be
implemented using code. The plan is to use either C++ or Python coding languages to
execute this allowing the scientists to easily operate the device. The next task is an
adjustable pulse amplitude and a user selectable pulse width and period. This is to
allow the scientists to adjust and differ the pulse to simulate variability when creating
the pulsars. Also it will allow the scientists the option to adjust and set the pulse wide
and period of the pulsar they desire.
Another task is polarization of pulses. This will represent the variety of different
phases a pulsar can be and will permit scientists to adjust the phase to see if the
outputs are correct with the digital backends. Another task is creating an independent
noise floor. In space, there are many other variables that could affect a pulsar when
travelling through the interstellar medium. To reproduce this effect, and independent
noise floor is to be put into place.
Lastly is to create sub pulses and interpulses. This would be a nice added
feature for the device. When studying actual pulsars, they sometimes create sub
pulses, which are pulses that are less strong emitted by a pulsar, and interpulses,
which is a pulse emitted to the opposite end of the pulsar. With this feature it added to
the device, it would accurately reproduce a real pulsar.
Design
Hardware
To make this device work, the hardware design will be crucial for creating
the approximate characteristics of an authentic pulsar. It is intended to use a
PIC microcontroller accompanied by RF components to produce the pulsar.
This will mean designing multiple high and low pass filters along with summing
amplifiers and wideband noise sources to generate the correct output.
Software
Along with hardware design, software is needed in the control of the
device. One example would be the need of having a user interface for the
device. It was suggested to use a simple coding language to create just a few
commands to operate the device. The idea is to use C++ or Python to allow
easy operation of the device. Also the microcontroller that will be used will also
need to be programmed. C++ is the intended language to program the chip
which will control the device.
Block Diagram
This diagram is the proposed plan to create the artificial pulsar. As you can see
in the design there are two noise sources. One will be used to create the pulsar and
the other will be used to create the independent noise floor. The noise source that
creates the pulsar will be passed through a series of high and low pass filters and then
a non-linear transmission line. By using the correct parameters for each of the
components, the device should be able to produce an artificial pulsar.
Implementation
To be able to create a device like this that will operate correctly, the correct
testing must be done. By working with the NRAO, it allows access to use of their
facilities and design and engineering tools. For example they have access to many
programs that can be used to test the design of the device. One is Eagle PCB which
allows schematic design and circuit board layout. Another is Microwave Office which
deals with RF/Microwave design and modeling.
Once the design is correct, the actual construction must take place. After finding
the correct parameters from testing, it need to find the correct components with those
parameters. This could be a difficult task depending on the results and could also be
costly. The idea to get the correct components for an optimal cost.
Conclusion
To conclude, the current artificial pulsar at the NRAO in Green Bank, WV is
outdated. The goal is to create an artificial pulsar that will be used by the NRAO, the
primary stakeholders for this device. It is important this device can perform the tasks
asked by the scientists to allow them to test their digital backends to and further the
development in pulsar research. Hopefully the design ideal for is need to be
accomplished and complete finished product can be delivered.
References
Appendix III – Summary of Changes
The main change to the project is that the project was extended to a two-year
project. With this change came the change that we no longer were going to provide a
prototype. Because the entirety of the project won't be complete until the next year, it
was unreasonable to build what is currently completed.
There was also the addition of creating a printed circuit board. This was not in the
original design specs, but it did not change anything in regards to overall design. The
PCB just created a clean way to go from design to build in only a single step.