This fractional-N synthesizer covers 15 to 25 MHz in 1 Hz steps. Most of the work is done by the 128-macrocell CPLD which hosts the reference and VCO dividers.
http://www.holmea.demon.co.uk/Frac2/Main.htm
An experimental fractional-N frequency synthesizer using a CPLD.
http://www.holmea.demon.co.uk/FracN/Synth.htm
http://www.intio.or.jp/jf10zl/vhfsg.htm
http://www.intio.or.jp/jf10zl/uhfsg.htm
also includes an RF detector probe and signal generator
http://www.northcountryradio.com/Articles/sigtrace.htm
http://www.intio.or.jp/jf10zl/ssbsg.htm
Frequency range of 150KHz to 12MHz over 5 ranges. may be amplitude modulated by internal 800Hz tone with approx. 30% modulation. Mains powered unit has maximum 4V pk-pk adjustable output level.
http://www.vintage-radio.com/projects/signal-generator.html
How to make a very nice and stable frequency synthesizer from Harvard. Includes schematics, block diagrams and parts lists. Very through design.
http://seti.harvard.edu/synth/index.html