The RFzero™ is an Arduino multi-purpose GPS controlled Si5351A RF unit. It can be used as a beacon (IBP, SPB, CW, FST4, FST4W, FT4, FT8, JS8, JT9, ModeX (JT65, Q65, …), PI4, WSPR, …), stand alone WSPR/FST4W transmitter, signal generator, VFO, QO-100 dual LO, low cost GPSDO, e.g. for 10 MHz, IC-9700 LO, 90 MHz frequency counter or … More than 40 programs, Arduino sketches, are integrated into the Arduino IDE, so you can write or modify the software yourself. With the RFzero Manager you don’t even have to know anything about Arduino to use the RFzero™.

The RFzero is designed by Johan, 5Q7J • Bo, OZ2M • Hans, OZ2XH • Steen, OZ5N.


The RFzero™ can generate frequencies from 2289 Hz and close to 300 MHz. At the same time 28 I/O pins are available and eight of those are via an ULN2803A power driver. The programming and configuration are done via the USB port, thus no extra hardware programmer is needed.

The RFzero™ has been developed for radio amateurs, RF enthusiasts and everyone else who wants to extend their Arduino skills in combination with RF. The RFzero™ board is largely compatible with the Arduino Zero and Arduino M0+ boards. However, it has been carefully designed for flexible use in RF applications and with attention to the frequency spectrum and stability performance. Many users say that the RFzero™ is the best Si5351A RF solution available.

The RFzero functional block schematic.

Using the RFzero you can learn how to program an RF device and other electronic circuits or you can learn about RF circuits if you are already skilled in software development. The setup is very flexible, you can roll your own programs from scratch or you can use the RFzero library and programs together with the Arduino Integrated Development Environment (IDE).

The RFzero key features are

  • GPS
    • u-blox NEO-7 GPS receiver with world leading documentation
    • On-board pre-amplifier supply via coax
    • SMA female input
    • On-board header for GPS data access from other units
    • Optional back-up from battery or super cap.
    • Optional USB port directly to the GPS receiver e.g. for computer time keeping
  • RF
    • Si5351A clocked at 27 MHz and measured continuously for maximum accuracy
    • Fundamental frequencies from 2289 Hz and close to 300 MHz
    • Harmonics can also be used with reduced spectrum performance, e.g. WSPR on 1,3 GHz is possible and for PI4 on 10 GHz via x96 multiplier
    • 1 mHz frequency resolution
    • Push-pull coupled outputs for more output and lower even harmonics, or
    • Combined outputs for two-tone signals, or
    • Quadrature I/Q outputs via optional U.FL sockets
    • Lowest phase noise/time jitter
    • On-board pads for custom filter
    • On-board RF decoupling
    • RF section can be further shielded
    • Separate voltage regulator for the RF section
    • Four layer PCB for optimum RF performance
    • SMA female output
    • 13 dBm output 400 kHz to 200 MHz
  • Micro controller
    • Arduino compatible (Arduino Zero and Arduino M0+)
    • 32 bits ARM M0+ processor running at 48 MHz and with 32 kB SRAM
    • 16 kB EEPROM
    • Optional EEPROM in tulip socket
    • USB port, with ESD protection, for programming and controlling purposes
    • ARM Cortex connector
    • Four SPI ports
    • Four I2C/Wire ports
    • Five serial ports
    • One Real Time Clock
    • Four status LEDs (on, TX, GPS PPS and GPS valid)
    • On-board LCD connector for either 3,3 V or 5 V LCD with contrast and backlight control
    • 28 I/O pins
    • Up to eight 12 bits analog inputs
    • One 10 bits analog (DAC) output
  • Separate voltage regulator for the digital circuitry
  • Darlington power driver IC ULN2803A in tulip socket e.g. for controlling relays
  • Possibility to add a shield for additional functionality or expansion
  • On-board test LED
  • On-board ground loop for alligator clip
  • 11 dedicated test points for easy troubleshooting
  • Half Eurocard PCB size that fits into a variety of boxes including a standard metal sheet box for best RF shielding
  • Power supply via USB or 5 V to 9 V to a terminal block
  • Gold immersion board for best assembly quality and life time performance

Download an RFzero presentation here.

The RFzero also has a user group at Groups.io.

If you want to add even more peripheral devices please feel free to get inspired from the Shop.