On Ebay I found dds pcbs. Those boards contain a 9850 dds chip and an oscillator.
It can be used for a synthesyzer from Hz up to to 40 MHz and more. I bought a few for my projects.
The DDS needs to be programmed. To do that I used a PIC based microcontroller board that I made for my spectrum analyzer project.
Programming the DDS is not that hard. The frequency in the DDS is controlled by writing a value to a 32 bit register. A few control bits must be set and that is it.
The 9850 is a well know chip so some sample code was available.
The biggest Software challenge was to display the frequency correctly. Some floating point calculations had to be done. Unfortunately the double datatype was to small for the calculation so I had to split it up.
Now It works prety good. This project can be the base for projects that need a synthesizer. First candidate is my 70 MHz to cb transverter. I need a 43 MHz signal for it. The DDS can deliver it but the output must be filtered using a bandfilter or a pll. This is needed because of the spurious signals that the DDS generates for signals >30 MHz.
Another project could be a 0-30 MHz CW transmitter. The spurious signals are within legal limits. A lowpass filter however is needed.
