Saturday, August 29, 2015

My version of Farhan's SPECAN

A couple of months ago I started to think about building a simple Spectrum Analyzer.  I thought using a simple Direct Conversion receiver might work for what most hams would need.  Looking around the Web I found a discussion with Ashar Farhan about this approach from a couple of years ago.  I e-mailed him to ask how it had turned out and mentioned some of my ideas of doing simple software image rejection.  He responded and listed some of the problems he had encountered, and gave me  information on the SA he ended up building based on theW7ZOI/K7TAU articles from QST.  Later he gave me a link to the blog entry he was working on discussing the project build, but asked me not to mention until he had finalized it. Earlier this week he finished the article and posed the link.

 This is an updated version of the W7ZOI/K7TAU S.A. replacing the vco with a si570 and the control and Scope interface replaced with an Arduino and a serial interface to a PC.  There is a corresponding piece of software on the PC that send control information to the S.A and receives and displays the acquired data.

I decided to build a stand alone S.A. based on this design.  I had been playing with different TFT displays for use in expanding the SNA Jr.  The one I liked most was a 3.2" 320x480 display, it is a nice large display that is designed for use with an Arduino Mega.

Using the Mega, it has a 16 bit parallel interface which is much faster than SPI that the others I had tried used.  I modified the design I had for a interface board to give the needed control and data lines needed for the S.A., also included some others for possible use in other projects.


Spectrum Analyzer Arduino Interface board
Did a quick board layout in Eagle and etched up a board so I could test the display.  I found that the display only needs the pins on the end connector and a connection to the RESET line on the Arduino.
This made layout easier than I thought it would be. and the board a little smaller. I did up a quick sketch to test the board with the appropriate drivers, and was pleased with the result.  Display is nice and large, and has more than adequate resolution for what I want to do. Since the driver graphic primitives are different and more limited than the ones I had used in the SNA jr. it is taking a while to port the software over to the new hardware.

  Since I already have the SNA jr and the Chinese SNA I can get to working on some of the S.A. boards.  The first board, was one I had already started on for expanding the SNA jr.  This was a detector board based on the ad8307, and is nearly the same as the W7ZOI board used in the PHSNA. Only change is that I had a bunch of 7805 regulators on hand and used that instead of a 78L05 , and used a buffer amplifier on the interface board. Later added a shield made from thin double sided PCB material around the detector part of  the board.

Now to lay out  and build some of the other S.A. boards.