Introduction
Several years ago I looked at receiving Marine HF Weather Fax broadcasts using the RTL-SDR & HF Up-Converter (Ref.1/2). In this post I will use the SDR-IQ HF receiver. The SDR-IQ was one of the first SDRs on the market and covers the HF band exclusively. I like it because it has excellent performance, is extremely rugged with metal case & BNC antenna connector and is USB powered for easy portable operation.
Equipment Setup
Figure 1 shows the equipment setup. An HF Buddipole is used as the antenna, although a suitable long wire would also work well (L>10m). The antenna connects to the SDR-IQ with RG-58/U 50ohm coaxial cable. The SDR-IQ is controlled by Spectravue software. WEFAX frequencies can be stored in the 20 memory channels available. The receiver is tuned to the required frequency in the USB mode. Decoded audio is sent to FLDIGI by Vb virtual cable.
Frequency Schedule
Fig.2 shows the Frequency Schedules taken from the NOAA pdf that contains schedules for the whole world (Ref.3). Only North American East Coast stations are indicated here. There is a detailed broadcast schedule for each station showing UTC Time vs. Contents of Transmission as well. Note that for a WEFAX signal at 6340.5KHz, the signal carrier frequency would be 6340.5 – 1.9KHz = 6338.6KHz since we operate in USB.
Reception
Figure 3 shows reception of Boston at 9110KHz and Figure 4 shows the decoding of the Fax signal in FLDIGI. Once the transmission is complete, the images can be saved with the Save command and are stored in C:windows/user/yourname/fldigi.files. Figures 5/6 show typical received FAXs.
HF-WEFAX Scicos Simulation:
https://jeremy-clark.ck.page/48e71d137c
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References
#1. – “OpenPlotter – Marine HF Weather Fax”
https://jeremyclark.ca/wp/telecom/openplotter-marine-hf-weather-fax/
#2. – “RTL-SDR for Marine HF Weather Fax”
https://jeremyclark.ca/wp/nav/rtl-sdr-for-marine-hf-weather-fax/
#3 – “Worldwide Marine Radiofacsimile Broadcast Schedules NOAA”
https://www.weather.gov/media/marine/rfax.pdf
#4. – “Spectravue Software”
http://rfspace.com/RFSPACE/Home.html
#5. – “FLDIGI Software”, W1HKK
http://www.w1hkj.com/
#5. – “Vb Cable”
https://vb-audio.com/Cable/
