Guido PE1NNZ has released code to enable the Raspberry Pi computer board to generate SSB on the 7 and 14 MHz bands.
“The following code can generate SSB modulation just by controlling a PLL carrier. I have applied this method on the RapsberryPi PLL, and made several contacts on 40m and 20m band with my RaspberryPi.” comments Guido
“The RaspberryPi receives the Microphone input via an external USB sound device. To improve the SSB quality, the signal is companded by a A-law compression technique. Three parallel BS170 MOSFETs where directly driven by RaspberryPi GPIO4 output to create about 1Watt of RF.”
“On 40m I could made several SSB contacts through Europe using this setup, receiving stations back by using a nearby online WebSDR receiver.”
Direct SSB generation by frequency modulating a PLL - http://pe1nnz.nl.eu.org/2013/05/direct-ssb-generation-on-pll.html