VFO-001

Features

• SDD1306 OLED Display
  • I2C Interface
  • OLED runs from 3.3V (can run from 5V but this use has 3.3V)
• Rotary Encoder Break Out Board
• Arduino Pro Mini
  • Arduino compatible
  • 3.3V
  • 8 MHz
  • Programmed via Arduino IDE
    • Download via serial
• Si5351 Oscillator Breakout Board
  • 10 KHz - 40 MHz tuning range
    • 1Hz/10Hz/100Hz/1KHz/10KHz/100KHz/1MHz/10MHz steps
  • I2C Interface
  • 3 Outputs
  • 27 MHz crystal
  • 3.3V operation works without level shifters for I2C*
  • Si5351 can only run from 3.3V
  • Used right angle headers and Dupont cables for low profile
• Mini-360 Buck Regulator
  • 5V-23V input
  • 3.3V output
• Extruded Aluminum Enclosure Box - 94mm x 83mm x 30mm

Schematic

• PWR* - connect only when no Mini-360 Buck Regulator is used
• PD01 - Power Distribution card (not shown)

Build

• Extruded Aluminum Enclosure Box - 94mm x 83mm x 30mm - Out of stock

• BNC/Power Jack placement

• Rear panel BNCs and power jack

• Drill holes and nibble out for OLED cutout
  • A bit rough
  • Better to undercut nibble and file to size

• OLED fitted

• Final

Libraries/Example Code

Land Boards Code

• Land Boards Application

VFO Menu

• Set Step Size
  • 1Hz, 10 Hz, 100 Hz, 1KHz, 10KHz, 100 KHz, 1 MHz, 10 MHz
• Set frequency
  • 10 MHz to 40 MHz in step size steps
• Select VFO
  • VFO0, VFO1, VFO2
• VFO On/Off
  • On, Off
• Drive Level
  • 2 mA, 4 mA, 6 mA, 8 mA
• Set Calibration Value
  • In step size steps (down to 1 Hz)
• Save [power-on] defaults

Libraries used in this app

• U8g2: Library for monochrome displays, version 2
• Si5351 Library for Arduino
• Rotary Encoder - Software debounced

Other Si5351 Libraries

• Universal Digital VFO Si570/Si5351
• Adafruit_Si5351
• Si5351 Library for avr-gcc
• vk3hn_VFO_controller
• Simple BFO with si5351 controlled by Arduino
• VFO and BFO with Si5351A, OLED and Arduino

Calbration Using WWV

• Good method that doesn't require a frequency counter
• Tune via ear and S meter
• Requires shortwave (or ham) receiver that can receive 5/10/15 MHz
• Rough tune calibration factor on scope or frequency counter
• Fine tune to 1 Hz using WWV
• 15 MHz WWV midday has better resolution

Measurements

• Channel CLK0
• 10 Mhz
• 30 dB external attenuator (gain set in tinySA to -30dB)
• Scan 1MHz to 300MHz

• Zoom into 10 MHz fundamental
• Approx. 1 dBm signal level

Si5351A Drive Level

• First, calculate the "theoretical" drive level and then measure the actual level into a 50 ohm load
  • Si5351A drives out a 3.3V square wave
  • Si5351A datasheet lists 50 Ohm source impedance
    • Half of the power would be dissipated in the source
  • The RMS value is for square-wave voltages whose pulse duration (ti) and pause (tp) have the same length:

• Square Wave Calculator

• "Theoretical" drive level of 3.3V

• 109 mW would be 20/3 dBm total power
• Half delivered to load = 54.5 mW
  • 17.4 dBm
• ADE-1 needs +7 dBm level
• Would in theory need a 10 dB attenuator
• Output drive in the Si5351A is controlled by the output drive control register
• Si5351A outputs measured with tinySA
  • Drive Level 2 mA = 0.2 dBm
  • Drive Level 4 mA = 6.2 dBm < Best choice for driving +7 dBm mixers like the ADE-1
  • Drive Level 6 mA = 9.7 dBm
  • Drive Level 8 mA = 11.7 dBm

Drive of 3.3V with 50 Ohms source/load impedances

Videos

• Charlie Morris YouTube channel