Direct Digital Synthesizer (DDS) VFO

Niras C V/VU3CNS

VFO Display with RIT ON

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.


  1. Range 0 to 70 MHz by 1 Hz step.
  2. Freq setting in 1, 10, 100Hz, 1, 10, 100KHz, 1, 10 MHz by using a low cost mechanical encoder with a variable tuning rate.
  3. 2 rows X 16 character LCD display.
  4. A 4 x 3 Keypad used for easy freq entry.
  5. IF, CW, SSB offsets settings when used with Transceiver/ Receiver.
  6. Software calibration to WWV or equivalent.
  7. Two VFOs and split freq operation.
  8. 19 user memories, memories freq + mode (i.e. LSB/USB etc.)
  9. All settings are held in EEPROM and are permanent (but user can change it any time).
  10. 4 Band selection and 4 Mode selection outputs.
  11. When operating below IF frequency, clockwise rotation of rotary encoder decreases DDS out put frequency but increases the display frequency.
  12. RIT operation.

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 [1] in this site. PCB designs are here [2]. I used Multi PIC programmer and IC-Prog [3] 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

[1] Hex file, Circuits, and Documents
[2] PCB Designs
[3] Multi PIC programmer

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