UHF Phase Modulation
The best way to go about doing this is basically bypassing the DDS altogether and generating the baseband from a DSP and generating the symbols using a IQ Modulator. A VCO based PLL can be used to generate an LO for the modulator.

Additionally, the magnitude of the I &amp; Q baseband voltages has the following relation:

Vq = -tan(10°) * Vi
Vq = -tan(-10°) * Vi