Wide Band Artificial Pulsar

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Overview

Many radio astronomy observatories located world-wide utilize sophisticated digital backends in support of both pulsar search and pulsar timing projects. At Green Bank, we currently operate GUPPI (the Green Bank Ultimate Pulsar Processing Instrument). In addition, we are about to embark upon the introduction of several pulsar modes into our latest digital backend -- VEGAS (the Versatile Green Bank Astronomical Spectrometer). For early commissioning tests and continued support of these advanced backends, we are currently in need of a new Wideband Artificial Pulsar which will very closely approximate the natural characteristics of an actual pulsar. More specifically, we wish to faithfully reproduce both the pulsar period (typically in ms) and the pulsar pulse dispersion through the Interstellar Medium as illustrated in the Figure below.

The creation of such a test instrument will facilitate autonomous qualification and quantification testing while removing reliance upon telescope and/or facility infrastructure availability. We are currently operating a 1^st generation Artificial Pulsar which has no provisions for representing pulse dispersion and is dependent upon the use of a standard laboratory signal generator for establishing the requisite pulse period, see below.

Specifications

• The BW should be user selectable and range from 100 MHz to 1000 MHz
• User interface should be through a set of simple commands from the shell. Not a GUI
• Amplitude of pulses above noise floor should be adjustable and variable from pulse to pulse
• Width (us - ms) and period (ms - s) of pulsar should be user selectable
• Polarization (phase) of pulses (X and Y) should be user selectable
• Noise floors should be independent in X and Y. The noise floor should not be polarized
• Sub pulses and/or inter-pulses

Current Progress

• The board hardware design and layout are done, see below for a block diagram and image of the current WBAP board.
• The control software for the Netburner motherboard will be coded by Zackary Parsons, an REU summer student at Green Bank Observatory.
• In need of a dispersive transmission line system in order to emulate the inter-stellar medium.

Hardware Measurements

• Eye diagram on the CS line to measure the timing jitter of the clock signal.
• 3 dB cut-off frequency for filters: through connection, 100 MHz, 200 MHz, 800 MHz for:
  1. Only the pulse connection
  2. Only the background connection
  3. Pulse and background together
• IP address 10.16.96.180

Documentation

SystemManual.doc

Data Sheets and Useful Links

Hardware

Noise generators: NC2_4000_Datasheet_WEB.pdf

Variable Gain Amplifier (VGA): MAX2064.pdf

Switches: hmc241qs16.pdf

Voltage regulators: LM7833.pdf and LM7833.pdf

Software

NetBurner: Datasheet-MOD5270-100-200IR.pdf

Quick start guide: MOD5270-LC-QS-Guide.pdf

Report: zackary-parsons-wbap-report.pdf

Pulsar Theory

http://www.cv.nrao.edu/~sransom/web/Ch6.html

Dispersive Transmission Line

Loaded line phase shifter: PhaseShifter.pdf

Non-linear TL modelling technique: FDTD_Analysis.pdf

S-parameters: http://www.microwaves101.com/encyclopedias/s-parameters

Microwave Engineering book: http://www2.electron.frba.utn.edu.ar/~jcecconi/Bibliografia/Ocultos/Libros/Microwave_Engineering_David_M_Pozar_4ed_Wiley_2012.pdf

• Section 2.1 on "The lumped-element circuit model for a transmission line"
• Section 2.3 on "Terminated lossless transmission line"
• Section 4.3 on "The Scattering Matrix" (S-parameters)

Paper on non-linear TL modelling technique: FDTD_Analysis.pdf

Microwave Office tutorial: Microwave_Office_Tutorial.pdf