Standalone HAM modulation generator

RTTY, Hellschreiber, WSPR, CW, PSK and QPSK 31,63,125

beacon light


  •    Audio modulation
  •    CIV system control
  •    Avoid using PC
  •    RTC DS3231 (no GPS)
  •    Mode « Standalone »
  •    PTT output (for older TRX)
  •    Cost € 20

The Standalone modulation generator is based on the following components:

  •     Arduino NANO
  •     DS3231 Module
  •     MAX232


This article was written at the request of Jaime. The idea is to be able to do generate WSPR and other modulation without PC, while using your TRX.

Main board description:


The DS3231 is used to synchronize time transmission(J4). Arduino Nano generate Audio frequency around 1500Hz(J3). RV1 adjust Audio level Output. CIV software serial via Max232 control VFO and PTT(J5). There is also another PTT output (2N2007 in open Drain J3). Power supply is 5 Volts, there is no DC/DC converter.


The audio sinus frequency is generated by Arduino PWM, so a low pass filter is required.



DDS generation

If you take a look at MODULATION.cpp file, there is only one sinus table (512 values). However it is possible to generate several audio frequencies.

The method is described here:

I change parameters to use it with 512 values PWM DAC. Sinus table is center to 128 (0, 255 range)

  • 1st I compute DDS word as follow:

dds part 1

  • 2nd In timer interrupt (Fc=13157.9 HZ, Tc=Te=76µs)

dds part 2

DDS word is accumulated in ACCU. The result is 23 bits right shifted to retrieve sinus value in the table. Why 23 bits? 32-23=9 : there is 512 sinus values , so 2^9=512.

Software description:

WSPR_TRX.ino is an experimental program and very short.

Source code and schematics in Hi res here

Update RTC before begin transmission :

update time : format yy,m,d,h,m,s

example : 2016,6,18,16,32,30

Program send audio signal every minute according to modulation table

2 Hellschreiber
4 CW
5 PSK and QPSK 31,63,125

txing(3); // send WSPR modulation

CIV is used for KX3 TRX. Change sentence according to your TRX.


It was a pleasure to study DDS and modulation generation. This project was designed essentially for makers. Adapt it as you want.If you have any questions :

Bill Of Materials

Resistors SMT 1206

  • 1    R1                  1K
  • 2    R3,R4               4.7k
  • 2    R5,R6               330
  • 1    R7                  10k


  • 4    C1,C3,C5,C6         100nF       SMT 1206
  • 1    C2                  100uF       classic  radial
  • 1    C8                  10uF
  • 4    C24-C27             1uF

Integrated Circuits

  • 1    U1                  ARDUINO NANO
  • 1    U2                  ICL232


  • 1    Q1                  2N7002


  • 1    J1                  ALIM
  • 2    J2,J4               CONN-SIL4
  • 1    J3                  PTT
  • 2    J5,J8               JACK_STEREO
  • 1    L3                  VK200
  • 4    PT1-PT4            Brace
  • 1    PT5                 GND
  • 1    RV1                 10K

Items Links



Standalone HAM modulation generator

Votre commentaire

Entrez vos coordonnées ci-dessous ou cliquez sur une icône pour vous connecter:


Vous commentez à l’aide de votre compte Déconnexion /  Changer )

Photo Facebook

Vous commentez à l’aide de votre compte Facebook. Déconnexion /  Changer )

Connexion à %s