I have placed a .pdf at http://www.knology.net/~gmarcus/WSPR/wspr2.pdf
that describes a 1 watt 30 meter homebrew SSB transceiver that I built specifically for WSPR operation. The transceiver uses single crystal notch filter at the LSB frequency to convert a basic direct conversion DSB transceiver into a SSB transceiver for WSPR.

Gene W3PM GM4YRE