Direct Digital Synthesizer (DDS) VFO
Niras C V/VU3CNS
DDS VFO Ver 3.2
This is a continuation of my previous DDS projects. This project uses PIC16F628A and AD9850 or AD9851. PIC16F628A is an 18-Pin microcontroller with 2K byte program memory, it is a FLASH-based and a member of the versatile PIC16F62XA family of low-cost, high-performance, CMOS, fully-static, 8-bit microcontrollers. PIC16F62XA devices have special features to reduce external components, thus reducing system cost, enhancing system reliability and reducing power consumption.
The AD9851 is a highly integrated device that uses advanced DDS technology to form a digitally programmable frequency synthesizer. AD9851 generates a stable frequency and phase-programmable digitized analogue output sine wave. This sine wave can be used directly as frequency source with an output tuning resolution of approximately 0.04 Hz with a 180 MHz system clock. The AD9851 contains 6 X REFCLK Multiplier circuits that eliminate the need for a high speed reference oscillator.
DDS VFO Ver 4.0
All features are same with DDS VFO 3.x releases, except it uses additional PIC for selection more band pass filters, i.e. 9 bands and a general coverage (out of all these bands).
The hex code to program PIC16F628A, Circuit and other detais are available at downloads  in this site. PCB designs are here . I used Multi PIC programmer and IC-Prog  to program the microprocessor. You will get further assistance through this site if required. Your suggestions and comments are always welcome and please put on Forums