HFVFO using an AD 9854 Direct Digital Synthesizer

HF-VFO using an AD 9854 Direct Digital Synthesizer Craig Johnson, AAØZZ FDIM 2003 May 15, 2003

AGENDA 1. Introduction 2. What Does A DDS Do? 3. Block Diagram 4. Hardware Description 5. Software Description 6. Results 7. HF-VFO with an R 2 Pro 8. Extensions 9. Concluding Remarks 10. Questions AAØZZ FDIM 2003 May 15, 2003

Block Diagram LEDs Encoder PIC Main PIC Push Buttons Clock DDS LP Filter Amp I out LP Filter Amp Q out Display AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock Frequency Tuning Word AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock Frequency Tuning Word AD 9854 FTW = Desired Freq X 248 ---------Frequency (Hz) AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock Frequency Tuning Word AD 9854 FTW = Desired Freq X 248 ---------Frequency (Hz) AD 9850 FTW = Desired Freq X 232 ---------Frequency (Hz) AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock Frequency Tuning Word Examples (125 MHz Clock) AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock Frequency Tuning Word Examples (125 MHz Clock) 1 Hz 1 MHz AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock Frequency Tuning Word Examples (125 MHz Clock) 1 Hz AD 9850: 1 MHz 34 AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W D A C DDS Clock Frequency Tuning Word Examples (125 MHz Clock) AD 9850: 1 Hz 1 MHz 34 ~34 Million AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock Frequency Tuning Word Examples (125 MHz Clock) 1 Hz AD 9850: 34 1 MHz 34. 359738 x 106 AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock Frequency Tuning Word Examples (125 MHz Clock) 1 Hz AD 9850: 34 1 MHz 34. 359738 x 106 AD 9854: AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock Frequency Tuning Word Examples (125 MHz Clock) 1 Hz AD 9850: AD 9854: 34 1 MHz 34. 359738 x 106 ~2. 25 x 106 AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock Frequency Tuning Word Examples (125 MHz Clock) 1 Hz AD 9850: AD 9854: 34 ~2. 25 x 106 1 MHz 34. 359738 x 106 ~2. 25 x 1012 AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock - On each clock pulse the DDS performs calculations AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock - On each clock pulse the DDS performs calculations based on: Frequency Tuning Word AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock - On each clock pulse the DDS performs calculations based on: Frequency Tuning Word Current phase AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock - On each clock pulse the DDS performs calculations based on: Frequency Tuning Word Current phase - The DDS does look-up in sine table AAØZZ FDIM 2003 May 15, 2003

What Does A DDS Do? 01101011 F T W DDS D A C Clock - On each clock pulse the DDS performs calculations based on: Frequency Tuning Word Current phase - The DDS does look-up in sine table - The D-to-A Converter (DAC) sets output voltages to desired levels AAØZZ FDIM 2003 May 15, 2003

Quadrature AAØZZ FDIM 2003 May 15, 2003

Block Diagram LEDs Encoder PIC Main PIC Push Buttons Clock DDS LP Filter Amp I out LP Filter Amp Q out Display AAØZZ FDIM 2003 May 15, 2003

Hardware Description • 2 PIC Microcontrollers • AD 9854 DDS • 5 -v Regulator • 3. 3 -v Regulator • 125 MHz Reference Clock • Low Pass Filter (30 MHz) • RF Amplifier (ERA-3 MMIC) • Optical Encoder (or Mechanical) • Pushbuttons, LEDs • Display (LCD) AAØZZ FDIM 2003 May 15, 2003

Prototype – Front AAØZZ FDIM 2003 May 15, 2003

Prototype – Back AAØZZ FDIM 2003 May 15, 2003

Software Description • Encoder PIC microcontroller • Main PIC Microcontroller • Display (LCD) • Pushbuttons and LEDs • Dual VFO (Split Operation) • Calibrate • AD 9854 Initialization AAØZZ FDIM 2003 May 15, 2003

Results • 2 Outputs – Quadrature (900) • 2 -v p-p (10 d. Bm) I and Q • 0 - 30 MHz • Used in R 2 Pro (Don Huff, W 6 JL) - “It’s HOT!” • 40 d. B Opposite Sideband Rejection -“ 40 d. B sounds astonishingly good” • Spurs? - “Low” (need more measurements) • Phase Noise? AAØZZ FDIM 2003 May 15, 2003

Prototype – Operational AAØZZ FDIM 2003 May 15, 2003

Prototype – LCD AAØZZ FDIM 2003 May 15, 2003

HF-VFO with an R 2 Pro Receiver (Rick Campbell, KK 7 B) VFO Antenna RF RF in Amp I Q Analog Downconverter Signal Processor Audio Filters Audio Amp Speaker AAØZZ FDIM 2003 May 15, 2003

Early Prototype Running R 2 Pro Don Huff, W 6 JL AAØZZ FDIM 2003 May 15, 2003

Extensions 1. Add a Phase Lock Loop (PLL) 2. Upgrade the 125 MHz reference clock 3. Try different filter(s), amplifiers 4. Add a CW sidetone 5. Add Transmit/Receive keying delay logic for dual VFO operation 6. Change the 5 -V Regulator 7. Add circuitry to change USB/LSB 8. Experiment with spread spectrum AAØZZ FDIM 2003 May 15, 2003

Conclusion • Stable, usable VFO - as is • Ready for your extensions • Learning tool § PIC microcontrollers § DDS AAØZZ FDIM 2003 May 15, 2003

Questions? AAØZZ FDIM 2003 May 15, 2003