Wideband Artificial Pulsar Signal Simulator

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 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

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

Extended Problem Statement

Background

Objective

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.