RTL-SDR for HF Beacons Propagation Prediction


Fig.1 Proppy HF Circuit Prediction NCDXF/IARU Beacons (Ref.4)

In a previous post, I looked at how the RTL-SDR can be used to receive HF stations in the NCDX/IARU HF Beacon network (Ref.1). These stations transmit on a schedule and can be used for HF propagation analysis. Various programs can also be used for HF propagation prediction (Ref.2), such as VOACAP (Ref.3) and Proppy (Ref.4). Proppy was developed by James Watson M0DNS, and is based on ITU-R P.533-14.

HF Beacon Reception Planning

Fig.2 HF Equipment Layout
Fig.3 NCDXF/IARU WebPage Active Transmission (Ref.5)

Figure 2 shows the HF equipment setup. A balcony mounted HF buddipole is connected to the 125MHz upconverter using RG-58. The upconverter feeds the RTL-SDR version 2. Reception is by SDR# with a shift of -125MHz to compensate for the upconverter. Figure 3 shows the active transmission schedule that can be accessed directly from the NCDXF/IARU webpage (Ref.5).

Each station transmits for 10 seconds, with the call at 22wpm followed by four one second dashes. The call and first dash is sent at 100W, the next dash at 10W, the next at 1W and the final at 100mW. Each station transmits on each band once every 3minutes. After transmission, it shifts to the next higher band.


Fig.4 Proppy Web Interface
Fig.5 Beacons Mode QTH_Rx Lat/Long & Ant
Fig.6 QTH_Rx & Beacon Locations & Prop Lines May 6th_2022
Fig.7 Propagation Prediction Table for QTH_Rx Month May 2022 on 14.1MHz
Fig.8 Propagation Prediction Table for QTH_Rx Month May on 18.11MHz

Figure 4 shows the Proppy web interface. There are four modes of operation: Area, Point to Point, Beacons and Planner. This makes it very useful for amateur operators or broadcasters and SWLs alike. Let’s examine the Beacons mode.

The first step is to add the Latitude & Longitude for the Rx location, or drag the small blue icon on the map. You have the option of selecting the Smoothed Sunspot Number SSN source and your antenna type as in Figure 5. Then run the program, the Rx & Beacon locations are shown in Figure 6 and the five propagation prediction tables are produced. Figures 7 & 8 show tables for 14.1MHz and 18.11MHz, the other 3 tables have virtually no openings and are not shown. Proppy has a detailed manual available to explain all the parameters. The table gives S numbers.

These are the results for my QTH:
Latitude = 43.7098deg N Longitude 79.4013degW
Date = Month May
SSN = Sunspot Number = 98

Looking at the tables, the best signal strength for my location occurs in the bottom left hand corner of the tables between 00:00 and 04:00 UTC on 14.1MHz and 18.11MHz. The best stations are CS3B/LU4AA/OA4B/YV5B, with YV5B at S6 on 14.1MHz being the strongest. In my previous beacon post April 12th, I received YV5B at 22:00UTC which is roughly in this window.

Rx Results

Fig9. Receiving CS3B Madeira at May 6th at 2302Z
Fig.10 CS3B Morse Signal 2302Z

This time around on May 6th, I received CS3B Madeira clearly at 19:02 EDT or 23:02UTC which correlates with the prediction.

Fig.11 YouTube Video RTL-SDR for HF Beacons Propagation Prediction
YouTube Channel
YouTube Channel


#1. – “RTL-SDR for HF Beacons”

#2. – “Propagation Tools and Resources for Contesting”, Ken Caruso W01N, Andrew Rodland KC2G, QST Magazine Nov 2021

#3. – “VOACAP – CHU to VE3PKC”,

#4. – “Proppy HF Circuit Prediction NCDXF/IARU Beacons”

#5 – “NCDXF/IARU International Beacon Project”

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.