The shortwave spectrum from 3 to 30 MHz holds radio signals from all over the world. Here is a compact overview of the most commonly used signal types.
Introduction to Shortwave Communication
Shortwave or high-frequency (HF) describes the band of electromagnetic frequencies from approximately 3 to 30 MHz. Radio wave propagation in this frequency range has some interesting properties: Shortwave radio waves can be reflected by the ionosphere back to earth. Therefore beyond line-of-sight communication over a long distance is easily possible. This is unlike communications at VHF / UHF or higher frequencies, where typically line-of-sight is required to build up a link, which often limits the range on ground to roughly 100 km.
Shortwave radios can communicate over many 1000 km. The actual coverage is influenced by the state of the ionosphere and changes over daytime, season and solar activity. When propagation conditions are good, often only little equipment is sufficient for long distance communication, e.g. a compact transceiver with some 100 W output power and an antenna.
In summary, the main advantages of shortwave or high-frequency (HF) communications are:
- Long distance coverage
- Simple equipment sufficient
- Independent from large-scale infrastructure such as satellites, sea cabels, etc.
- Hard to block by third parties
Due to these advantages many operators are using shortwave signals for communication including aviation, maritime, military, amateur radio, intelligence services and embassies (diplomatic).
Because of the potentially world-wide coverage, a single radio can receive many different signals from operators all over the world. Various modulation formats are present, of which some are easy to identify (e.g. Morse). However, the large number of different signals present in the spectrum can make signal identification a hard task.
The well-known signal database sigidwiki.com lists over 220 different shortwave signal modulations. A similar number of modes is listed in Roland Prösch’s “Technical Handbook for Radio Monitoring”. However, many of the listed signals appear only very rarely in the spectrum or are outdated and no longer used.
From my experience roughly 100 shortwave signal types are used on a more or less regular basis in the shortwave HF band. Below an overview of these most commonly used signal types are given. It presumably covers > 95 % of the signal types one may find in the spectrum.
Overview of Shortwave Signals
General Signal Types
| Mode | Modulation | Bandwidth | Waterfall Image |
|---|---|---|---|
| Morse Code | on-off-keying | depends on keying speed |  |
| USB Voice | single-sideband (upper) | 2500 Hz |  |
| LSB Voice | single-sideband (upper) | 2500 Hz |  |
| AM Broadcasting | amplitude modulation | often 10, 15, 20 kHz |  |
| DRM Broadcasting | OFDM | 5, 10 or 20 kHz |  |
Amateur Radio Modes
Ham radio amateurs heavily use the shortwave spectrum for extensive communication in the decicated amateur bands. The most frequent modes are SSB voice, Morse code and digimodes like RTTY, PSK or FT4 & 8. In addition, a wide variety of other digital modes are frequently used.
| Mode | Modulation | Bandwidth | Waterfall Image |
|---|---|---|---|
| Ardop | adaptive mode with single and multi-tone FSK and PSK | 200-2000 Hz |  |
| Contestia 8/250 | 8-MFSK, 31 Bd | 250 Hz |  |
| Contestia 16/250 | 16-MFSK, 16 Bd | 250 Hz |  |
| Contestia 32/1000 | 32-MFSK, 31 Bd | 1000 Hz |  |
| Dominoex 11 | 18-MFSK, 11 Bd | 260 Hz |  |
| FreeDV | different OFDM modes | 1000 / 1600 Hz |  |
| FT-4 | 4-GFSK, 23 Bd, 4.5 s burst duration | 80 Hz |  |
| FT-8 | 8-MFSK, 6 Bd, 12.6 s burst duration | 50 Hz |  |
| Hell (Feld) | on-off-keying | 75 Hz |  |
| JT-9 | 9-MFSK, 1.7 Bd | 16 Hz |  |
| JT-65 (A) | 65-MFSK, 2.7 Bd | 180 Hz |  |
| MFSK-16 | 16-MFSK, 16 Bd | 300 Hz |  |
| Olivia 8/250 | 8-MFSK, 31 Bd | 250 Hz | |
| Olivia 8/500 | 8-MFSK, 62 Bd | 500 Hz |  |
| Olivia 16/500 | 16-MFSK, 31 Bd | 500 Hz |  |
| Olivia 32/1000 | 32-MFSK, 31 Bd | 1000 Hz | |
| Packet 300 | 2-FSK, 300 Bd / 200 Hz shift | 300 Hz |  |
| Pactor 1 | 2-FSK, 100 or 200 Bd / 200 Hz shift | 300 Hz |  |
| Pactor 2 | 2 tone PSK | 450 Hz |  |
| Pactor 3 | adaptive: 2, 6, 14, 16 or 18 tone PSK | 400 – 2200 Hz |  |
| Pactor 4 | adaptive: chirp, BPSK to QAM | 2400 Hz |  |
| PSK-31 | BPSK, 31 Bd | 80 Hz |  |
| PSK-63 | BPSK, 63 Bd | 160 Hz |  |
| PSK-125 | BPSK, 125 Bd | 320 Hz |  |
| Robust Packet | OFDM with PSK | 500 Hz |  |
| ROS 8 | 144-MFSK, 8 Bd | 2300 Hz |  |
| ROS 16 | 144-MFSK, 8 Bd | 2300 Hz |  |
| RTTY 45 / 170 | 2-FSK, 45 Bd, 170 Hz shift | 200 Hz |  |
| RTTY 75 / 170 | 2-FSK, 75 Bd, 170 Hz shift | 200 Hz |  |
| Sitor-A | 2-FSK, 100 Bd, 170 Hz shift | 250 Hz |  |
| SSTV | various analog types such as Martin, Scottie or Robot | 2400 Hz |  |
| Thor 11 | 18-MFSK, 11 Bd | 260 Hz |  |
| Throb 4 | 9-MFSK, 4 Bd | 150 Hz |  |
| Vara HF | adaptive: single and multi-tone MFSK, BPSK, QPSK, 8-PSK, 16-QAM, 32-QAM | 500 / 2300 Hz |  |
| Windrm | different OFDM modes | 2300 / 2500 Hz |  |
Aviation and Maritime
Aviation and martime operators use shortwave signals to communicate weather, emergency and operational information over long distances where line-of-sight communication is not possible.
| Mode | Purpose | Modulation | Bandwidth | Waterfall Image |
|---|---|---|---|---|
| GMDSS-DSC | Maritime Comms | 2-FSK, 100 Bd / 170 Hz shift | 250 Hz |  |
| HFDL | Aircraft Position Data | PSK bursts | 2400 Hz |  |
| ICAO Selcal | Aircraft selcall before voice link | two two-tone codes | 1500 Hz |  |
| RTTY 50 / 450 | Weather data | 2-FSK, 50 Bd / 450 Hz shift | 500 Hz |  |
| Wefax | Weather maps and data | analog HF fax | 2400 Hz |  |
| Sitor-B / Navtex | Maritime Information | 2-FSK, 100 Bd / 170 Hz shift | 350 Hz |  |
Governmental, Diplomatic & Military
Signals from governmental, diplomatic and military users are often proprietary and not well documented in public. Therefore the real users, purposes and even signal names may remain obscure and information is typically not confirmed. The shortwave spectrum is heavily used by NATO, Russia and Japan, but also by many other countries. Especially Russia uses shortwave frequencies extensively for diplomatic and military purposes and transmits – from a technical point of view – some of the most interesting modulation formats.
| Mode | Origin | Modulation | Bandwidth | Waterfall Image |
|---|---|---|---|---|
| CIS-12 | Russia | 12 tone OFDM | 3000 Hz |  |
| CIS-36 (Serdolik) | Russia | 36-MFSK, 40 Bd | 1400 Hz |  |
| CIS-36-50 | Russia | 2-FSK, 50 Bd, shift 200 or 250 Hz | 300 Hz |  |
| CIS-45 | Russia | 45 tone OFDM | 3000 Hz |  |
| CIS-60 | Russia | 60 tone OFDM | 3000 Hz |  |
| CIS-112 | Russia | 112 tone OFDM | 3000 Hz |  |
| CIS-75/250 | Russia | 2-FSK, 75 Bd, 250 Hz shift | 400 Hz |  |
| CIS-200/1000 | Russia | 2-FSK, 200 Bd, 1000 Hz shift | 1000 Hz |  |
| CIS-3000 | Russia | 8-PSK, 3000 Bd | 3400 Hz |  |
| CIS-OFDM 121 | Russia | 121 tone OFDM | 3000 Hz |  |
| CIS-1200/800 | Russia | FSK, 1200 Bd, 800 shift | 1500 Hz |  |
| Mazielka | Russia | 6-MFSK | 250 Hz |  |
| XPB | Russia | 16-MFSK, 66 Bd | 2800 Hz |  |
| XPA2 | Russia | 14-MFSK, 7.5 Bd | 250 Hz |   |
| Chinese 4+4 | China | 8 QPSK carriers | 2500 Hz |  |
| Chinese Data Link 30 | China | 30 carrier BPSK | 2500 Hz |  |
| DPRK-FSK | North Korea | 2-FSK, 600 or 1200 Bd / 600 shift | 1600 Hz |  |
| Israel Navy Hybrid | Israel | MS-118-110A serial with characteristic preamble | 2400 Hz |  |
| Japan 8 Channel | Japan | 8 tone 2-FSK | 2400 Hz |  |
| Japan 32 Channel | Japan | 30 BPSK carrier + sync/pilot | 2400 Hz |  |
| Japanese Slot Machine | Japan | QPSK, 1500 Bd | 2000 Hz |  |
| Mahrs-ALE | Germany | 8-PSK, 2400 Bd | 2600 Hz |  |
| MHF-50 | South Africa | 33-MFSK with 2-FSK preambles | 2200 Hz |  |
| Pol Intel 4 FSK | Poland | 4-FSK, 100 Bd | 1500 Hz |  |
| ALE-2G (MS-188-141A) | various | 8-MFSK, 125 Bd | 2400 Hz |  |
| ALE-3G | various | 8-PSK, 2400 Bd | 2800 Hz |  |
| FSK 50/850 | NATO | 2-FSK, 50 Bd / 850 shift | 1000 Hz |  |
| GM-2100 | various | very similar to Link 11 Slew | 2500 Hz |  |
| Link 11 Slew | various | 8-PSK, 2400 Bd | 2500 Hz |  |
| Link 11 Clew | various | 16 tone QPSK | 2500 Hz |  |
| Link 22 | NATO | QPSK / 8-PSK, 2400 Bd | 2800 Hz |  |
| MS-118-110A serial | NATO | 8-PSK, 2400 Bd | 2500 Hz |  |
| Stanag 4197 | NATO | 39 tone OFDM QPSK | 2300 Hz |  |
| Stanag 4285 | NATO | 8-PSK, 2400 Bd | 2800 Hz |  |
| Stanag 4481 FSK | NATO | 2-FSK, 75 Bd / 850 Hz shift | 1000 Hz |  |
| Stanag 4539 | NATO | QPSK up to 64-QAM, 2400 Bd | 2800 Hz |  |
| Codan | various | 16 tone QPSK | 1800 hz |  |
| Panther-H | various | Frequency Hopper, QPSK, 2400 Bd | 2500 Hz |  |
| Thales Skyhopper | various | Frequency Hopper, 8-MFSK & QPSK | 2000 Hz |  |
| OTHR / Radars | Russia, China, Nato | fast repetitive sweeps | typically 3- 50 kHz |  |
Time Signals
Time signal stations convey information on the current time.
| Station | Origin | Waterfall Image |
|---|---|---|
| BPM | China, Chinese Academy of Sciences |  |
| CHU | Canada, Institute for National Measurement Standards |  |
| RWM | Russia |  |
| UTC | USA, National Institute of Standards and Technology, Stations: WWV & WWVH |  |
Channel Markers
In the lower parts of the shortwave spectrum various stations can be found, that transmit repeating odd sounds. These shortwave signals do not convey any information, but their purpose is to keep the frequency occupied. Many of these signals have been given figurative names describing the sounds they make. Probably the most well-known signal is the “The Buzzer”, which has received some wider public attention. The channel markers are mostly attributed to Russian operators.
| Mode | Frequency | Waterfall Image |
|---|---|---|
| The Alarm | 4770 kHz |  |
| The Airhorn | 4930 kHz |  |
| The Buzzer | 4625 kHz |  |
| The Goose | 3243 (night) or 4310 kHz (day) |  |
| The Pip | 3756 (night) or 5448 kHz (day) |  |
| The Squeaky Wheel | different |  |
| T-Marker | 4182 kHz |  |
Further Reading
- sigidwiki.com (large collection of shortwave signals, some signals outdated)
- priyom.org (detailed information on HF number, military and diplomatic stations)
- Roland Prösch: Technical Handbook for Radio Monitoring HF
- Utility DXers Forum
