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Pulsar Detection

2003

A Progress Report

By

James Van Prooyen N8PQK

grro@dnx.net

SARA 2003

Annual Meeting

Summary

Development and testing of Version 2 of the pulsar detector is nearly complete.

Version 2 is a complete rewrite of the detection system with a number of bugs fixed and several new features added to the system.

Overview

Version 2 of the program continues to use the Radio Astronomy Supplies (RAS)

406.7 MHz system and it associated software. The only difference is an additional parameter in each data file to record the seconds past midnight.

This accuracy is needed for processing the data in the detection system.

The named scan function is used to record the name of the pulsar that will be observed. The data collection rate (know as DT) is set to "0.1" seconds.

After data collection is complete the data is passed to the pulsar processor

(RA_PSR2).

Input Files

The input files to the pulsar detector can have any name but must be in the

format used by the RAS receiver. The format is as follows:

            "Pulsar J Name","Date/Time",Seconds Past Midnight, DT

            0,Voltage

            2,Voltage

            N,Voltage

            360,Voltage

Please note the addition of "Seconds Past Midnight", this is used to fix data collection timing problems that existed in version "1" of the pulsar detector.

A modified version of RAS's program "RA.EXE" was created called "RA_21.EXE" and it has the above listed changes.

Processing File

The pulsar detection system is made up of several different files

RA_PSR2.BAS         Source code file for the pulsar detector

RA_PSR2.EXE         Executable program

RA_PSR2.CAT         The catalog of 1300 know pulsars

RA_PSR2.CMD        The command file, this has information on the

                                    data files to be processed.

RA_PSR2.SET         Setup data

Output Files

The output file has arrays of data for plotting in Excel. Currently there are 4 different data arrays saved for plotting, they are as follows:

Example data file which are plotted in this report are:

            PSR76.DAT

            PSR269.DAT

            PSR1117.DAT

            PSR1133.DAT

            PSR1161.DAT

Please note that the internal catalog name is used, many older operating systems will not support the naming standard currently in use for naming pulsars.

Processing

The pulsar detector works in the following manner. The signal is sampled using 

a time base that is some integral fraction of the period of the pulsar. Each

sample taken during the duration of a single pulse period is assigned to a bin. The sample can then be folded back so that samples from corresponding bins

are added together. Each time we add a new series of bin values for the ongoing totals, we "renormalize" by subtracting an amount from all of the bins so

that the weakest bin value is brought back to zero. Random noise in each bin tends to average out and bins, which have a slightly higher average, will gradually "grow" above the others. A picture then emerges which shows how the average strength of the pulsar signal varies over it's period.

A filter based on the pulsar period is then used for final processing of the data.

data is sent to a file, the file name is selected from the catalog based on its index in the catalog.

Bugs Fixed

The following known bugs have been fixed in this version of the pulsar detection system.

1. Data collection timing. This was fixed by adding a parameter to the output file

    that records the number of seconds past midnight when data collection stared

    for this record.

2. User interface to complex, this was fixed be using a command file and

    removing the user interface.

Bugs Not Fixed

The following are known bugs that have not been fixed.

a.  Dispersion, due to the fact that the RAS receiver has a band width of only

     75 KHz, and this version of the detector uses fixed bin's (0.1 second in width),

     dispersion corrections would have had little value, when most pulsars that

     have  a dispersion of less the 1000. Wider bandwidth receivers will need to

     have adjustments for dispersion. The pulsar catalog does have the dispersion

     value for each pulsar.

b. Allow batch processing of data.

c. Add additional filters

d. Add additional processing to allow the system to look into each data file to see

    if it adds value to the data being processed.

e. Fix minor plotting problems by adding a user selectable plot filter to the

    program.

Data

The following are data plots from several different pulsars.

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