Introduction
In the last few posts (Ref.1/4), I examined the WSJT-X protocols FT8 & WSPR using the RTL-SDR, HRF1 and PlutoSDR. In this post I will look at receiving FT8 using the RTL-SDR and MULTIPSK (Ref.5). MULTIPSK is an incredibly versatile Ham Radio software program that has recently added FT4rx, FT8rx & WSPR to it’s capability.
Reception Block Diagram
Figure 1 shows the equipment block diagram. In this case I am using an Alex Magnetic loop for reception. The first step is tune the loop for maximum output at the FT8 band frequency. For the majority of FT8 HF bands, the 125MHz upconverter is used, although for 10m and up this is not required. The first method of reception on MULTIPSK is to use audio only. In this case SDR# could be used as a receiver with audio output sent to VB cable. In the MULTIPSK start screen, the audio input is set to VB cable as in Figure 2. However, MULTIPSK can control the RTL-SDR directly, so SDR# is not necessary. In this case set the audio input back to default, detect your RTL and set the RTLkey/DLL which will control the RTL as in Figure 3.
FT8 Reception on MULTIPSK
When you press the Rx/Tx screen the transceiver control appears on top of the decode window as in Figure 4. Enter and forward the required frequency. In this case 125MHz has been added to the 20m FT8 frequency = 125 + 14.074MHz = 139.074MHz. After several minutes the decodes will appear.
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References
#1. – “PlutoSDR for WSPR Beacon on GNURadio”,
https://jeremyclark.ca/wp/telecom/plutosdr-for-wspr-beacon-on-gnu-radio/
#2. – “HRF1 for WSPR Beacon on GNURadio”,
https://jeremyclark.ca/wp/telecom/hrf1-for-wspr-beacon-on-gnu-radio/
#3. – “RTL-SDR for WSJT-X FT8”,
https://jeremyclark.ca/wp/telecom/rtl-sdr-for-wsjt-x-ft8/
#4. – “RTL-SDR for WSJT-X WSPR”
https://jeremyclark.ca/wp/telecom/rtl-sdr-for-wsjt-x-wspr/
#5.- “MULTIPSK”, Ham Radio Software, F6CTE
http://multipsk.fr/index_anglais.html
