VGAtoBaseband

VGAtoBaseband Release status: experimental [box doku]
Description	use the VGA port to generate I/Q baseband signals
Author(s)	siro
Last Version	0.1 ⁽⁾
Platform	Evil Hack
License	GPL
Download	[1]

Requirements

PC with VGA adapter
OpenGL with Direct Redering
Vsync enabled
Software-defined Radio Transmitter that generates I/Q Signals
GL_ARB_fragment_program to use the low-pass filter
GL_ARB_pixel_buffer_object for efficient CPU to GPU transfers

Linux

Mesa 9.0 (other drivers are untested)
X-server

Windows

Windows XP doesnt work
other OS are untested

Software

This software generates analog I/Q Signals that can be feed into a rf-modulator. The current version runs on any symbolrate, recommended are 5MSymbols/s or more.
You need to set the DAC clock to 7*desired MSymbols per second,because low pixel clocks might not work and high pixel clocks can be scaled down by using multiple pixel per Msymbol (here 7).
For 9.142 MSym/s set 64Mhz. To do so use xrandr:

*xrandr command here*

A symbols contains an I and Q value. By default the signal is lowpass filtered using convolutional sinc function. To edit the impulse response edit the file fragment.glsl. The I/Q values are feed using a unix fifo / a file. 8 byte form two 32bit floats, that equals a complex number. The values have to be between 0.0f and 1.0f. The complex value is assigned to the RED and GREEN channel, while the BLUE channel is set to 0.5f. 8bit and 10bit VGA Graphic cards are supported.

Bandwidth

OFDM useful carriers to total carriers ratio: 1705 / 2048 = 0.832

DAC clock [Mhz]	Msymbols/s	carrier ratio	Bandwidth
64	9.14285	0.832	7.61
56	8.000	0.832	6.66
48	6.8571	0.832	5.71

Arguments

./vgatoiqbaseband inputfile [OPTIONS]

OPTIONS can be:

-nofilter        disable fragmentshader
-v               be verbose
-verbose         be verbose
-cutofright <n>  cutof n rightmost pixels (hsync)
                 default:  1
-cutofbottom <m> cutof m bottommost pixels (vsync)
                 default:  2

Libraries

freeglut3-dev
libglu1-mesa-dev
libgl1-mesa-dev