The schematic of the SDR Transmiter accessible via the link http://yu1lm.qrpradio.com/homebrew.htm shows only a single input beiung used from the soundcard with no additional audio phase shifting for generating I/Q parallel streams to feed the quadrature mixer. So only a DSB signal (no image cancellation) can ever be formed
For an SDR transmitter you MUST somehow generate I/Q audio streams in parallel to mix with the quadrature LO, for subsequennt sideband cancellation / reinforcement. This can either be done in op-amps using all pass filters, or, these days, more commonly in DSP using a Hilbert trasform or audio quadrature mixing technique for 'random' source data like voice. Data modes and tones can, of course, be generated directly with 0 / 90 degree shift, and there are several utilities for doing this. I have some software written by G3PLX and previously mentioned on this group, that will take in microphone input and generate two parallel audio streams with 90 degree phase shift between them. It also includes an SSB clipping / speech compression function, automatic microphone level control, and AM/FM options with a trick for getting round the soundcard's DC response null. There's also a 1kHz tone for CW and testing, a fine tuning capability to offset the signal by a few 100Hz, LSB/USB switching and phase / amplitude trimming controls. All-in-all, a pretty comprehensive but easy to use little package! Feed the Left and RIght outputs from this software into your 4066 switches (using a pair of inverter op-amps to give the four 0/90/180/270 degree signals) and you should manage good opposite sideband cancellation. You can download the G3PLX software from my website: http://www.scrbg.org/g4jnt/SDRProjects.htm Andy G4JNT www.scrbg.org/g4jnt
