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

Abstract2

Introduction4

Extended Problem Statement4

Background4

Objective5

Design Achievements6

Hardware Design7

Eagle PCB Layout7

Materials8

Reflections9

Appendix I – Block Diagrams10

Appendix II – Original Design Proposal14

Appendix III – Summary of Changes45

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 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.

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

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

Introduction3

Extended Problem Statement4

Background4

Objective5

Requirements Specification6

Marketing Requirements8

Overall architecture of the system9

User Interface Specification10

Software specifications to the function level11

Test Plans13

Project Management Plan15

Appendix 1 – Project Website17

Background – Green Bank Telescope20

Background – Pulsars21

Project Design/Needs22

Objective Tree23

Stakeholders25

Conclusion26

References27

HYPERLINK \l "_Toc405413163"

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 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.

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 variable-setting 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. .

"Pulsar." Merriam-Webster. Merriam-Webster. Web. 22 October 2014. .

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-randy-mccullough

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. .

"Pulsar." Merriam-Webster. Merriam-Webster. Web. 22 October 2014. .

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.

�Illustration � SEQ "Illustration" \*Arabic �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.

�Illustration � SEQ "Illustration" \*Arabic �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 � SEQ "Illustration" \*Arabic �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.