WSPR is part of a suite of communication protocols developed by Dr. Joseph Taylor K1JT, a Nobel Prize winning pulsar researcher (Ref.1). He applied the latest signal processing techniques from his astronomical research to the reception of very weak amateur radio signals. Amateur radio operators can work at signal to noise ratios bordering on -28dB, unheard of up to that time! Dr Taylor was recently profiled in QST magazine (Ref.2) and his original paper from 2010 is available on line (Ref.3). WSJT-X is available for download (Ref.4).

WSPR Weak Signal Propagation Reporter

Fig.1 WSPR Block Diagram

Figure 1 shows a block diagram of the WSPR process. Messages are very compact and consist of Call Sign, Maidenhead Locator and transmit power level in dBm for a total of 50bits (Ref.5). These bits are then inputed to a convolutional encoder, interleaver and synchronizer to produce a data frame of 162 symbols. The LSB is a sync bit and the MSB is a data bit. Modulation is 4FSK with tone separation = symbol rate = 1.4648Hz. WSPR transmission travels mostly by reflection from the ionospheric D/E/F layers. Reception reports can be uploaded to WSPRnet real time to show world wide propagation (Ref.6).

Figure 2 shows the so called spots or WSPR reception for the 20m & 30m bands at 14:30EST in the afternoon on New Year’s Day 2023. Reception was carried out shortly before & after this time.

WSPR Rx Equipment Setup

Fig.3 WSPR Receive Equipment Setup
Fig.4 WSPR Receive Equipment

Figure 3/4 shows the receive equipment setup. An Alex Magnetic Loop PY1AHD was used, which is connected to a HamItUp 125MHz converter and RTL-SDR. Reception is by SDR# and output is sent via VB cable to WSJT-X WSPR software. Figure 5 shows the SDR# screen for 30m and Figure 6 shows received spots on 20m & 30m.

Fig.5 SDR# Setup WSPR 30m
Fig.6 WSJT-X WSPR Decode 20m & 30m

Scicos Simulation

Fig,7 ScicosLab WSPR 4 Level Code for FSK

Figure 7 shows ScicosLab code used to generate a random stream of 4 level 1.4648baud data to drive an FSK VCO. Figure 8 shows the Scicos model to simulate 4FSK WSPR transmission. Figure 9 shows the 4 level data and spectrum.

Fig.10 YouTube Video RTL-SDR for WSJT-X WSPR

Please send your comments, questions and suggestions to:

YouTube Channel
YouTube Channel


#1. – “WSPR”

#2. – “Dr. Joseph Hooton Taylor, Jr. K1JT”, ARRL QST magazine Jan 2023

#3. – “WSPRing Around the World”, J.Taylor K1JT, B.Walker W1BW

#4. -“WSJT Download”

#5. – “WSPR Coding Process”, G4JNT,

#6. – “WSPRnet.org”

By Jeremy Clark

Jeremy Clark is a Senior Telecommunications Engineer and Advanced Amateur Radio Operator VE3PKC. He is the author of E-Books on Telecommunications, Navigation & Electronics.