Introduction
In previous posts I looked at decoding GMDSS/DSC signals using Multipsk (Refs.1/3). Recently I have been able to use my balcony again and receive HF & VHF signals. This evening I was able to receive a VHF Ch70 GMDSS/DSC coastal signal on 2m using SDR# & Multipsk.
GMDSS/DSC VHF Reception
| Parameter | MF/HF | VHF |
| Frequency | 2187.5, 4207.5, 6312.0, 8414.5, 12577.0, 16804.5 KHz | 156.525MHz |
| Baud Rate | 100 | 1200 |
| Character | 10bits (#s 00-99) Error Correcting Code b1-7 info b8-10 parity | 10bits (#s 00-99) Error Correcting Code b1-7 info b8-10 parity |
| Frame | 6-7secs | 0.5secs |
| Modulation | J3E USB(300,2700) nom 1700Hz/+-85Hz d_Mark/Space=170Hz | F3E/G3E NBFM 1700Hz/+-400Hz d_Mark/Space=800Hz |
| BW | 800Hz | 3500Hz |
Figure 1 shows a summary of the HF/VHF DSC parameters. Figure 2 shows the VHF Equipment Block diagram. Figures 3/4 show the SDR# receive and Multipsk decoder screens.
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References
#1. – “RTL-SDR for HF Marine GMDSS/DSC
https://jeremyclark.ca/wp/telecom/rtl-sdr-for-hf-marine-gmdss-dsc/
#2. – “RTL-SDR for Marine GMDSS/DSC on RaspberryPi4”
https://jeremyclark.ca/wp/telecom/rtl-sdr-for-marine-gmdss-dsc-on-raspberrypi4/
#3. – “RTL-SDR for Marine GMDSS/DSC on Multipsk”
https://jeremyclark.ca/wp/telecom/rtl-sdr-for-marine-gmdss-dsc-on-multipsk/
#4. – “GMDSS A User’s Handbook”, Denise Brehaut, 6th Edition, Adlard Coles
https://www.amazon.ca/dp/B071JXWBWC/
#5.- “GMDSS Global Maritime Distress and Safety System”
https://en.wikipedia.org/wiki/Global_Maritime_Distress_and_Safety_System
#6. – “ITU-R M.493-15 Digital Selective Calling System for use in Maritime Mobile Service”
https://www.itu.int/rec/R-REC-M.493-15-201901-I/en
#7. – “GMDSS HF & VHF Wav Files”
https://www.sigidwiki.com/wiki/GMDSS_Digital_Selective_Calling
#8. – “Audacity”
https://www.audacityteam.org/
#9.- “MULTIPSK”, Ham Radio Software, F6CTE
http://multipsk.fr/index_anglais.html
