Generating high frequency sine wave (up to 100MHz)
Consider building an oscillator that can be swept over a range from 80 MHz to 160 MHz (typically a Colpitts oscillator) and mix (using a 4 quadrant mixer) the output with a fixed frequency of 80 MHz. The difference frequency (wanted) can be extracted from the mix and will range from DC to 80 MHz. The sum product (unwanted) will range from 160 MHz to 240 MHz and can be removed with a fairly good low pass filter.
You can also use a variable oscillator frequency of 200 MHz to 280 MHz and mix with a fixed frequency of 200 MHz (for example). The difference will still range from DC to 80 MHz but the sum (unwanted) will be 400 MHz to 480 MHz and a little easier on the low pass filter design.
Stability control will be an issue but, if you use a decent phase-locked-loop and some digital control then it becomes more stable (just like how DDS works really).