General purpose RF IQ modulator using VGA graphics DAC

Copyright (C) 2011 Elkhazin Copyright (C) 2011-2015 Rashid Mustapha [[email protected]]

http://github.com/dabfree http://opendigitalradio.org/

VGAMod is free software; you can redistribute it and/or modify it under the terms of the General Public License V3 as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version.

VGAMod is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the General Public License 3 for more details.

You should have received a copy of the General Public License V3 along with VGAmod; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

INTRODUCTION

VGAmod is a proof of concept Software Defined Radio IQ modulator signal generator inspired by the amazing work of Fabrice Bellard (www.bellard.org). Certain functionality was cribbed from the author of VGAsig, an FM transmitter by Bartek Kania.

It can be used to generate a modulated RF signal from the VGA DAC from either an a file of IQ samples (32-bit complex floats) or stdin. See http://opendigitalradio.org

INSTALLATION

Dependencies: the SDL library must be installed.

gcc -O3 VGAmod.c -lm -lSDL -o VGAmod

gcc -O3 testmod.c -lm -lSDL -o testmod

USAGE

./VGAmod -w [width] -W [wtotal] -h [height] -H [htotal

-r [rate]

-c [CarrierFreq]

-s [SampleFreq]

-i [InputFile]

-C [CarrierSignalShift]

-I [InputSignalShift]

-O [OutputShiftRight]

-M [OutputMask]

-L [OutputShiftLeft]

TO DO

1. Fix testmod.

2. Fix slight frequency drift is reported between the input/carrier and vsync clocks. This show up as a slight drift left or right in the carrier/input signals. There is no obvious reason for this. You can try playing with the vsyncOffsetSignal/ vsyncOffsetCarrier parameters. You could also try a mutex around the buffer red/write pointers, but the volatile declaration should do the trick.

3. Add ZeroMQ input

4. Interpolation and filtering?

5. Create as GNURadio sink?

PEOPLE

Elkhazin Rash [email protected]

REFERENCES

(Inspired by:)

http://www.bellard.org/dvbt/

(Features/ideas poached from)

http://bk.gnarf.org/creativity/vgasig/

(For)

http://opendigitalradio.org