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On-line satellite spectrum analyser

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Spectrum analyser project

The idea: To make an on-line satellite spectrum analyser which is able to point to various satellites.

The system is no longer working so this page is here to explain how I did it, in case someone else wants to give it a try.

In order to connect to the internet I needed a server.  The only one I have here is an old SparcStation10.   Advantages: Easy to program, gcc complier works well and reliable.  Can work php and perl also if needed.

Because it would be much easier to physically interface with a PC (using National Instruments a/d and digital i/o board) and a plug in GPIB board I seriously considered using a PC but I was not happy to even contemplate using Microsoft software in a server and learning how to set up Linux with the interface boards was an unknown.   I decided to use the SUN machine and the programs to be in C since that was the only way to get the SUN GPIB board to work.

Problems to be solved:

1. Getting a GPIB board to connect the HP8560A to the SUN.   Obtained a SBUS GPIB board via Ebay. (about 15 years old)

2. Getting software drivers for SUN SBUS GPIB board.   From National Instruments (note only in C code)

3. Writing software to produce a gif file.  Use gd software package. (see credits below)

4. Writing C software.  Use gcc to generate a cgi file to deliver the gif file in response to http request.

5. Writing software to respond to web page requests.  Note return of web page html text not used, the program return a gif image only.  (see credits below)

6. Sending messages to the motor, to the LNB (hi/low volts and 22kHz tone) and reading analogue antenna position:  Used SUN serial port B and ByVac BV4113 stepper motor controller.

Progress report 28th March 2007:

The SparcStation10 is working well with Solaris 9, and I have developed C program software that will convert 601 measurement values into a gif image (see example below).

I have obtained an S-BUS GPIB interface board ( National Instruments NI SB-GPIB ) via eBay that is now physically installed in the SparcStation10

Problem:  I have a more recent, and incompatible, software package NIpcigpib.   I need to downgrade the software NI-488.2 to SB-GPIB or GPIB/TNT.  I think it is called NICsbgpib.   

Example outputs so far:

This first spectrum analyser image is a 601 x 601 pixel gif file.

Drawing xy graticule and diagonal line with gd software

It incorporates two colours:

grey = gdImageColorAllocate(im, 128, 128, 128);
white = gdImageColorAllocate(im, 255, 255, 255);

There is a white line plotted from top left to bottom right and graticule graticule lines drawn up/down and across.

/* draw test line from top left to lower right */
gdImageLine(im, 0, 0, 600, 600, white);
/* plot graticule line down the middle */
gdImageLine(im, 300, 0, 300, 600, grey);
/* plot graticule line across the middle */
gdImageLine(im, 0, 300, 600, 300, grey);

This second spectrum analyser image gets rid of the experimental lines above and now incorporates some useful spectrum analyser screen graticule lines, shown in green.

gd software - testing gif image

green = gdImageColorAllocate(im, 0, 255, 0);

These are plotted using c code like:

/* plot graticule line down */
gdImageLine(im, 0, 0, 0, 600, green);
gdImageLine(im, 60, 0, 60, 600, green);

 /* plot graticule lines across */
gdImageLine(im, 0, 0, 600, 0, green);
gdImageLine(im, 0, 60, 600, 60, green)

In addition a spectrum analyser plot is shown (in white)  comprising some test data numbers in an array of 601 elements. the majority of the numbers in the array are 293.  Note that they are plotted with larger numbers downwards.  I will have to fix this later.  If you leave an array variable undefined in C it comes out as anything and the image is a load of white spikes.

22 April 2007:  Today managed to get the serial interface B on the SPARC to talk to the BV4113 stepper motor controller.  First managed to do it with Hyper-terminal then with c program commands:  Set up of serial port is

fd = open(sPortName, O_RDWR | O_NOCTTY | O_NDELAY);
my_termios.c_cflag = B9600 | CS8 |CREAD | CLOCAL | HUPCL | CSTOPB;
my_termios.c_lflag &= ~(ICANON | ECHO | ECHOE | ECHONL | ISIG);

Connected up 12 volt supply for motor in differential mode and tested the following commands.

MA1 motor start moving left
MA2 motor start moving right
MA0 motor stop

Tried and tested Ok running it to the limit switches each way.

Attached 10k potentiometer to output and read the position 0 - 1023 in text initially, then in two hex bytes which makes it easier to put into an int value.

Program developed so as to send short run bursts in either direction.

Problems with non-linearity of potentiometer, so ordered a replacement high quality 2k pot.

13 May 2007 mounted dish in garden with manual motor control.

15 May first operation with computer control.  Obtained first full spectrum image remotely via web site page.

17 May.  Changed antenna position input data format from two bytes binary to variable number of ASCII characters.   The binary input occasionally contained break characters

Spectrum plot with text in gif image using gd software
Vertical polarisation down.   Significant carrier 11.668 GHz 39.7 Msps  Europe beam

The ripple in the noise floor baseline is disappointing. It may be due to very old satellite TV LNB and poor match at cable ends. 

Credits and copyright statements relating to the gd software:

Credits and copyright statements relating to the gd software subroutines:

Credits and license terms

In order to resolve any possible confusion regarding the authorship of gd, the following copyright statement covers all of the authors who have required such a statement. If you are aware of any oversights in this copyright notice, please contact Thomas Boutell who will be pleased to correct them.


Portions copyright 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004 by Cold Spring Harbor Laboratory. Funded under Grant P41-RR02188 by the National Institutes of Health.

Portions copyright 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004 by Boutell.Com, Inc.

Portions relating to GD2 format copyright 1999, 2000, 2001, 2002, 2003, 2004 Philip Warner.

Portions relating to PNG copyright 1999, 2000, 2001, 2002, 2003, 2004 Greg Roelofs.

Portions relating to gdttf.c copyright 1999, 2000, 2001, 2002, 2003, 2004 John Ellson (ellson@graphviz.org).

Portions relating to gdft.c copyright 2001, 2002, 2003, 2004 John Ellson (ellson@graphviz.org).

Portions relating to JPEG and to color quantization copyright 2000, 2001, 2002, 2003, 2004, Doug Becker and copyright (C) 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004 Thomas G. Lane. This software is based in part on the work of the Independent JPEG Group. See the file README-JPEG.TXT for more information.

Portions relating to GIF compression copyright 1989 by Jef Poskanzer and David Rowley, with modifications for thread safety by Thomas Boutell.

Portions relating to GIF decompression copyright 1990, 1991, 1993 by David Koblas, with modifications for thread safety by Thomas Boutell.

Portions relating to WBMP copyright 2000, 2001, 2002, 2003, 2004 Maurice Szmurlo and Johan Van den Brande.

Portions relating to GIF animations copyright 2004 Jaakko Hyv?tti (jaakko.hyvatti@iki.fi)

Permission has been granted to copy, distribute and modify gd in any context without fee, including a commercial application, provided that this notice is present in user-accessible supporting documentation.

This does not affect your ownership of the derived work itself, and the intent is to assure proper credit for the authors of gd, not to interfere with your productive use of gd. If you have questions, ask. "Derived works" includes all programs that utilize the library. Credit must be given in user-accessible documentation.

This software is provided "AS IS." The copyright holders disclaim all warranties, either express or implied, including but not limited to implied warranties of merchantability and fitness for a particular purpose, with respect to this code and accompanying documentation.

Although their code does not appear in the current release, the authors also wish to thank Hutchison Avenue Software Corporation for their prior contributions.

END OF COPYRIGHT STATEMENT More details here: http://www.boutell.com/gd/

Credits and copyright statements relating to the cgic software:

Credits and License Terms

cgic can be used free of charge, provided that a credit notice is provided online. Alternatively, a nonexclusive Commercial License can be purchased, which grants the right to use cgic without a public credit notice.

Thanks are due to Robert Gustavsson, Ken Holervich, Bob Nestor, Jon Ribbens, Thomas Strangert, Wu Yongwei, and other CGIC users who have corresponded over the years. Although the implementation of multipart/form-data file upload support in CGIC 2.x is my own, I particularly wish to thank those who submitted their own implementations of this feature.

More details here: http://www.boutell.com/cgic/

29 May 2007:  Increased the centre frequency resolution to 1 kHz step size.  Needed extensive char character to long integer conversion work doing.  Added the possibility of a software frequency adjust parameter in 1 kHz steps.  Note accuracy is still about +/- 1 MHz due to DRO type LNB.   Initial estimates are that displayed signals have freq error of +950 kHz.

30 May 2007:  Dismantled the garden mounted antenna.

31 May 2007:  Removed 2m band beam off pole at end of house and attached the antenna instead. It was a major job requiring the use of a rope to lift up the antenna end and of the pole.  Looks hopeful.  Will have to resolve clearances with a TV antenna.   Re-terminated outdoor end of cables and sealed up the angle potentiometer.  Motor drive, potentiometer and coaxial cables will be much shorter eventually.

Final result:

Started 25 Feb 2007, amended 21 June 2021     Eric Johnston.  Copyright Satellite Signals Ltd, 2007 All rights reserved.