In previous posts, I looked at receiving weather information over NOAA (Ref.1), GOES (Ref.2) and HF WEFAX (Ref.3). Various weather agencies also transmit marine weather information over HF SITOR (Simplex Teletype over Radio). SITOR is an RTTY teletype system with advanced features of error detection, redundancy and re-transmission not included in the regular Baudot RTTY. There are two types of SITOR:
SITOR_A/AMTOR-A: Error Detection, ARQ if error detected
SITOR_B/AMTOR-B: FEC error correction
NAVTEX for marine weather runs over SITOR-B. Detailed information is contained in the bible of radio codes from Klingenfuss (Ref.4)
NWS National Weather Service (US)
Figure 1 shows the US Coast Guard schedule for weather transmissions (Ref.5). Figure 2 shows the schedule for HF SITOR weather. Boston (NMF) is the closest station to my location. Broadcasts are at 9:40pm EDT and 12:30pm EDT. NBDP stands for Narrow-band Direct Printing.
RTL-SDR HF SITOR Reception
Figure 3 shows the equipment block diagram. HF signals are received on an HF Buddipole antenna and feed a HamItUp 125MHz upconverter connected to an RTL-SDR. Figure 4 shows reception on SDR# with a shift = -125MHz set to compensate for the Up Converter. Signals were received on 12579KHz on June 13th at 0140UTC. Reception was saved as a WAV file on SDR#, then later opened in Audacity as shown in Figure 5. The Audacity output was piped to VB cable into MULTIPSK (Ref.6) for decoding as shown in Figure 6. For reception in USB mode, set the carrier frequency lower than listed by about 1KHz.
#1. – “RTL-SDR for NOAA Satellite Weather on RaspberryPi4”
#2. – “RTL-SDR for Satellite Weather on GOES16 – Image Capture”
#3. – “RTL-SDR for Marine HF Weather Fax”
#4. – “Radio Data Code Manual”, Edition 18, Section 5.32 SITOR p.169″, Klingenfuss Publications, 2008
#5. – “Marine Weather Broadcasts from the USCG”
#6. – “MULTIPSK”