Peter Martinez G3PLX has written a small stand-alone piece of Windows / PC software for a Software Defined Transmitter. The software is intended to run as a companiom to the various SDR receivers out there to give a transmit and receive capability.
The program takes its input from a microphone and generates the I / Q signals as a stero output pair for driving a quadrature image cancelling upconverter. As well as Upper and Lower Sideband Peter has included AM and FM modes, having developed a crafty technique involving a subaudible tone to overcome the lack of DC response on PC soundcards. A tone generator allows CW and testing; there is automatic microphone gain adjustment and the ability to fine tune the phase and amplitude balance between channels. The carrier frequency can be offset from the centre by a few kHz if desired. The software can run on a single soundcard for input and output, or it can make use of two soundcards (freeing up the other half of each for other purposes). The software and a full description of the process can be found on my website, at the URL given below. To kick-off hardware building, I have included details of three I/Q upconverters developed over the years. Two for HF use - a simple quickie design using NE612 chips, and a high spec one with carrier/sideband balance for lab / testing purposes. Also, one for 144MHz primarily aimed at driving the IF for microwave transverters. There are a few ideas and pointers at other routes, especially for microwave use. Many thanks to Peter for coming up with this software so quickly after I mentioned it to him last week. He is still tweaking it slightly, so modified versions may appear from time to time. It has been tested so far with Windows XP, 2000 and NT, and works fine - we haven't tried any other operating system. Andy G4JNT www.scrbg.org/g4jnt www.scrbg.org/g4jnt/SDRTransmitters.htm
