(Please note that this program will not run without a valid GPS signal)

The FST4W beacon program makes the RFzero capable of transmitting on any frequency from 100 kHz to 200 MHz and beyond running on the fundamental frequency.

The configuration is done via the USB port. It is possible to wait for the RFzero to warm up for up to 255 s before starting to transmit.

When transmitting the TX LED will flash at half the symbol rate.

When GPS signals are received the PPS LED flashes ones per second and when the status of the GPS signal is valid the Valid LED is lit.

A PA can be controlled on/off on D7, i.e. off during no transmission to save power.

The beacon sequence

When the GPS time is valid the beacon transmits the selected FST4W sub-mode, i.e. FST4W-120, FST4W-300, FST4W-900 or FST4W-1800, then waits for then next cycle to arrive before the sequence repeats again.

If the GPS signal is invalid the beacon suspends the transmission.


To setup the type of display used please use the “wr display” command. If you want to change what is shown on the display please edit the display.cpp file.

Please see the display page for more information.

LCD 16×2

The display shows the UTC odd/even minute and seconds, the GPS status, the number of satellites and the HDOP.

Example of an LCD 16×2.

LCD 20×4

The display shows the GPS status, the number of satellites, the HDOP as a bar graph, the UTC, call sign and locator of the beacon and the frequency.

Example of an LCD 20×4.


The configuration of the program is done via the USB port, 9600 Baud, 8 bits, no parity and one stop bit, using a terminal program (e.g. Arduino IDE Serial Monitor, Termite Terminal (Windows), CuteCom (Linux) or Terminal (Mac OS)). Please connect the RFzero via a USB B cable to your computer and connect the terminal program to the right COM port in the terminal program. The RFzero identifies itself as an Arduino Zero (Windows Device Manager).

If you don’t see the RFzero> or RFzero config> prompts please press the enter key. When you want to execute a command you don’t have to enter the prompt but only the command and parameters after the >.

Changes to the configuration does not take effect before leaving the configuration mode.

All input to the RFzero must be in lowercase.

To enter the configuration mode please enter   config   at the RFzero> prompt, i.e.

RFzero> config

To see the available commands please enter   ?   at the RFzero config> prompt, i.e.

RFzero config> ?

To leave the configuration mode please enter   exit   at the RFzero config> prompt, i.e.

RFzero config> exit

When in configuration mode, i.e. when you see the RFzero config> prompt, the most frequent commands are

rd cfg

to see the configuration that will be used after exiting the configuration mode.

wr defaults

to set most of parameters to their default values. Please see the actual program for the specific default values.

wr t1 MODE

to set the T1 H/W mode where MODE is

  • 0: Transformer (default)
  • 1: Combiner
  • 2: None

wr display MODE

to set the display mode where MODE is

  • 0: None
  • 1: LCD 16 characters and two lines, HD44780 interface
  • 2: LCD 20 characters and four lines, HD44780 interface
  • 3: LCD 16 characters and two lines, HD44780 via I2C PCF8574 interface
  • 4: LCD 20 characters and four lines, HD44780 via I2C PCF8574 interface
  • 5: Graphics display, ILI9341 SPI interface
  • 6: Graphics display, ILI9488 SPI interface

wr bcn CALL

where CALL is the beacon call sign. The maximum length for the call sign in a Type 1 messages (call sign, square and power) is six characters and it must include a number, e.g. OZ0RF. The maximum length for the call sign in a Type 2 messages (compounded call sign and power) is ten characters and it must include a number, e.g. OH0/OZ0RF.

Please see the FST4W specification for more details about the message types.

wr loc LOCATOR

where LOCATOR is the locator up to eight characters, i.e. AA00AA00. But not all may be transmitted.

wr pwr POWER

POWER is the total system power level in dBm, i.e. after further amplification and cable loss etc. The RFzero doesn’t change power. Only the values below are valid. If you can’t find an exact match pick the closest one.

  • 0 dBm = 1 mW
  • 3 dBm = 2 mW
  • 7 dBm = 5 mW
  • 10 dBm = 10 mW
  • 13 dBm = 20 mW
  • 17 dBm = 50 mW
  • 20 dBm = 100 mW
  • 23 dBm = 200 mW
  • 27 dBm = 500 mW
  • 30 dBm =  1 W
  • 33 dBm =  2 W
  • 37 dBm =  5 W
  • 40 dBm =  10 W
  • 43 dBm =  20 W
  • 47 dBm =  50 W
  • 50 dBm =  100 W
  • 53 dBm =  200 W
  • 57 dBm =  500 W
  • 60 dBm =  1 kW

wr mode MODE

where MODE is the FST4W sub mode

  • 0: FST4W-120, starting at even minutes, i.e. 0, 2, 4, 6, 8, 10, 12, 14, … 58
  • 1: FST4W-300, starting at minutes ending with 0 or 5, i.e., 0, 5, 10, … 55
  • 2: FST4W-900, starting at minutes 0, 15, 30 and 45
  • 3: FST4W-1800, starting at minutes 0 and 30

wr freq FREQ

where FREQ is the nominal on-air beacon frequency in Hz from 100 kHz and up.

wr warmup SECONDS

where SECONDS is the number of seconds to wait for the RFzero to warm up.

wr level LEVEL

where LEVEL is the drive strength current in the output stages. This effectively changes the output power by up to 10 dB, but varies somewhat with frequency. Valid LEVEL values are

  • 0: 2 mA
  • 1: 4 mA
  • 2: 6 mA
  • 3: 8 mA, default level

To read more about the drive strength current please consult the Si5351A datasheet.

wr echo MODE

  • 0: hide all NMEA strings
  • 1: show the $GPGGA and $GPZDA NMEA strings
  • 2: show the $GPGGA, $GPGLL, $GPGRS, $GPGSA, $GPGST, $GPGSV, $GPRMC, $GPVTG and $GPZDA NMEA strings

More commands are available so please enter a question mark (?) at the RFzero config> prompt to see them.

Update the WSPRnet locator database

If you want to update your locator in the WSPRnet database please click here.