SARC WSPR Beacon

WSPR (pronounced “whisper”) is an acronym for Weak Signal Propagation Reporter, a mode designed by the famous Joe Taylor K1JT.  The WSPR signal includes a station’s callsign, Maidenhead grid locator, and transmitted power in dBm.  The WSPR protocol is used to report on propagation from weak signal sources to give the user and hams across the globe a good indication of what propagation paths are open on a given frequency during a selected time period. The result, such as the one for 20m shown in the image, tells us where our signals are being heard; propagation for VE7SAR and other stations can be viewed here.

At SARC, we wished to continuously test the effectiveness of our wire antenna on all 7 of the HF bands between 80m and 10m, using a custom-designed unit that would be superior to what is available commercially or in kit form.  The idea for a WSPR beacon came from Dino Gueorguiev VE7NX, who collaborated with Pierre F6IDT in France.  Pierre, a talented builder of electronic gear, generously supplied design information and printed circuit boards, so we are grateful to him for this hands-across-the-oceans willingness to share his expertise.  Since Pierre doesn’t speak English and Dino doesn’t speak French, email communication was facilitated by Google Translate!   

The WSPR beacon was constructed as a club project by 10 more experienced members, building their own device under the direction of Dino.  It was not a simple project and challenged our abilities.  For example, the device required low-pass filters, wound laboriously on tiny toroids and tested with VNA, for each band to produce clean, harmonic-free signals on the output.   

The WSPR is a stand-alone unit, controlled by an Arduino Nano.  The heart of the project is a Si5351C clock chip used to generate various frequencies. 

To clean the signal, four low-pass filters (LPF) were used instead of bandpass filters (BPF), automatically switched to the corresponding band.  Also introduced was a 2x16 character LCD display for visual confirmation of the selected frequency.  The power amplifier was a challenge since it was difficult to produce uniform power output from 80m to 10m.  Programming of the Arduino Nano was performed by Pierre and Dino.  

Since the WSPR signal is digital, linearity was not critical, and the power amplifier was operated as an efficient Class C.  A selector allows either single band operation or “hopping” mode, which transmits each band transmission for 2 min before moving on to the next band.  To ensure timing accuracy, a GPS receiver was provided for synchronization.

To complete the project, custom gold-plated front and rear panels were created for the enclosure.

At SARC, a nominal power of 5W is delivered to an off-centre fed dipole, which is resonant (or close enough) on all the HF bands.   At SARC, the beacon runs continuously except when the antenna is co-opted for another purpose, such as a contest.