WSPR Transmitter using Wemos D1 Mini

This is the 3 Band version of WSPR transmitter.

output power set to about 100mW.

Wemos D1 Mini and OLED shield

IoT has become very cheap now days.. cheaper than Arduino in fact.
It has more power and capacity. Also built in WiFi is definitely a big plus.

If you already know Arduino, going to IoT is not taking too much effort.

Here IoT device, a Wemos D1 Mini. It has WiFi and therefore, can get accurate (well to some point) enough from the Internet.

So, why not use IoT module as WSPR transmitter ?

WSPR transmitter requires that it begin transmission at the begining of even minutes. NTP information is used to synchronize the IoT and send WSPR codes as QPSK to DDS.

The WSPR codes here is a static information consisting 160 code that has to be sent every 682mS. Since the code is static, I generate the code using PC and put it into the Arduino sketch.



AD9850 DDS module is used here, since I already have it for long time ago and never been used.

The connection from Wemos to AD9850 is done at breadboard. Using SPI interface, the connection is done using 4 wire (W_CLK, DATA, FQ_UP and RESET).

Above was the initial testing. Surprisingly, the signal was heard in China and Japan.

That make me more eager to do more experiment. A buffer amplifier may be a next thing to try. Small PCB for prototyping here :

Here is the setup on my desk. Oscilloscope is used to get power measurement.
I got about 18 dBm using just 5V. Not free of harmonics though ....