RadCom May 2020, Vol. 96, No. 5

Introduction I have been making amateur radio projects for many years, not only for myself but in an effort to captivate students’ interest. In particular, I concentrate on the younger people who may wish to consider obtaining an amateur radio licence. Many of my own projects are complex and require a decent level of electronic understanding, but I also have some that are a little more general. The project described here is aimed at people who know how to program an Arduino and have the ability to wire up components on a breadboard ² WKH VRUW RI OHYHO RQH ÀQGV TXLWH ZLGHO\ LQ WKH ‘maker’ community. Project overview The idea of the project is to generate a WSPR signal with an AD9850 direct digital synthesiser (DDS) controlled by an Arduino. WSPR requires precise time synchronisation, so I use a DS3231 real-time clock to be sure of operating in the correct time slots without needing any external reference. The level of programming has been limited to the simplest that can be arranged – a simple loop FOR to transmit the WSPR signal. The assembly can be wired on a breadboard, perfboard or similar, step by step, in such a way that the constructor can test the various functions as they are installed. The project lets you learn KRZ WR SURJUDP D ''6 KRZ WR FUHDWH +) ÀOWHUV (without calculations!) and how to adjust the transmission frequency. Characteristics of the WSPR transmitter Based on an Arduino Nano microcontroller with Arduino IDE 1.0+ support, the system operates from +5V provided by a USB port or an external source. There are two uncommitted input/output (I/O) pins that may be used for whatever you want – perhaps a GPS connection. The frequency is set by an AD9850 DDS programmable oscillator, which feeds a simple EURDG EDQG DPSOLÀHU EDVHG RQ D %6 WR provide nominally 100mW of RF, which is plenty IRU :635 7KH RXWSXW RI WKH DPSOLÀHU LV ULFK LQ harmonics so the design includes a removable ÀOWHU WKDW \RX FDQ VZDS ZKHQ \RX FKDQJH EDQGV Accurate timing is ensured by a DS3231 real time clock (RTC) module. An optional OLED display can be added to provide operating and status information. Figure 1 shows the basic relationship between the modules. Although the project can be constructed perfectly successfully on prototyping breadboard or similar, I have designed a professionally-produced PCB that provides a neat solution, as seen in Photo 1. Photo 2 shows a prototype built on a solderless breadboard, just to prove that it can be done. WSPR information Weak Signal Propagation Reporter, universally referred to as WSPR and pronounced ‘whisper’, is a protocol designed and implemented by Joe Taylor, K1JT. It is used for very low power radio communication over long distances. Transmitters periodically send a signal that starts precisely on the minute mark. The signal lasts for about a PLQXWH DQG ÀIW\ VHFRQGV DQG LV VR QDUURZEDQG that hundreds of transmitters can operate on closely offset frequencies within the bandwidth of a SSB signal. Receivers all round the world NHHS D OLVWHQLQJ ZDWFK RQ VSHFLÀF IUHTXHQFLHV – usually 24 hours a day – and use digital signal processing techniques to extract all of the educational WSPR transmitter May 2020 37 Technical An Anthony Le Cren, F4GOH/KB1GOH kb1goh@yahoo.fr PHOTO 1: Modules used in the WSPR transmitter project, mounted on the PCB. FIGURE 1: General arrangement of modules.