intro GPS-project

FPGA's are very interesting chips. With software you can create a piece of hardware. A PCB with a programmed FPGA on it behaves as if it is a PCB with a microntroller with some hardware. That is the outside view. The inside view is completely different.

I got a software defined radio in an FPGA-chip on a PCB, the SDR4000 from DSPTools, and decided to develop something with that board. Firstly I decided to make an automatic multichannel CW-receiver but I discovered some programs on the internet that did exactly that!

Then I decided to experiment with GPS-hardware and software. A pretty useless exercise because you can buy a GPS-receiver for less than 50 euro...

But the only purpose of this project is to get experience with GPS, DSP, VHDL, java and some VHF-hardware. I read some books about DSP-processing and GNSS. I found data-files on the internet that represent actual mf-signals from a GPS-receiver. I wrote programs in java to decode that signal, a recording of about one minute. I wrote some plotting software, found FFT-source-code on the internet and finally found the PRN-codes and frequencies of some satellites. After that I got stuck in the tracking loop. That is where I am now in November 2010. I will first try to get most of my findings on this website and later go on to actually finish the software.

In my previous life at WUR, Wageningen University, the Netherlands, I had almost unlimited access to MATLAB, a marvelous software package. If you use that in combination with Xilinx's System Generator you can define and express your software problems in Simulink and port your code directly to VHDL and into the FPGA. However, I am a retired engineer now, no longer affiliated with the university and the Mathwork seems no longer interested in me. I could use a demoversion of the software but after a few month the game is over. Therefore I decided to go for straight VHDL, handcoded by myself and use C for interfacing and java for the main program. My purpose is to learn things while experimenting, not to build something that can be bought for about 50 euros.

I learned a lot sofar!

73, de PA1KDG (you can reach me at pa1kdg AT