I have completed a signal generator that uses the
Analog Devices AD9850 DDS.
The generator has the following features:

- Uses two 16F84 microcontrollers, one for a 4x4 keyboard,
  the other for LCD, encoder, DDS, shift-register as DAC
- Range 0.1 - 40MHz
- Steps selectable from 1, 10, 100Hz, 1, 10kHz
- Step multiplier selectable from 1-9
- Frequency entry through keyboard in 1Hz precision
- Keyboard commands to sweep frequency up or down
- Keyboard command to 'wobble' frequency in 250 steps,
  with corresponding DAC voltage for oscilloscope
  X-input.
- Output level from 0 - +10dBm, level is held constant
  within 1dB over range.

The 'wobble' function is particularly useful for
making measurements on filters. Using a log-detector
whose output is connected to an oscillocope Y-input
and the DAC output to the X-input, the filter's
response can be observed on the oscilloscope screen.
'Wobbling' is rather slow, I use an old memory scope
for this purpose.

The combination of selectable step / multiplier
allows for flexibility in choosing a 'wobble' range.
When using 1Hz steps, the 'wobble' range could be
250 Hz (mult=1) to 2250 Hz (mult=9), for 10kHz steps, this
would be 250kHz - 22.5MHz.

Documentation, schematics, sources are available at:
http://www.geocities.com/CapeCanaveral/Lab/9595/

Note that this is a hobbiest project. The result is
not a professional piece of test equipment, but rather
an example of how one could construct a cheap
alternative, useful for homebrewing RF stuff.

Comments are welcome,

Charlos Potma
charlos.potma@rivm.nl