I have added a slight update to the Quadrature Phase Modulator circuit. Merely a 1:1 current balun at the output so you can see how that works. The final output into the stage you add to follow the circuit is represented by the 2.5K load resistor on the output.
The circuit might look large in the schematic but it is made of 6 small signal transistors, a few caps and resistors along with two toroid transformers and so, is not a very large circuit at all when constructed. The reactance of the components in T1 and T2 are all 2.5k in case you want to change the circuit for use on another frequency. And, you will have to balance the signal input levels for that new frequency. You might want to added a low pass filter at the output for good measure. You should then be able to add this to a transceiver and use it. If not for anything but QPSK or try out the HamDRM or the Dream DRM transmitter with its I/Q outputs. http://groups.yahoo.com/group/soft_radio/files/SDR%20Spice%20Analysis%20Files/Quadrature_Phase_Modulator.zip Dan
