Latest update:  25-Apr-2010 (added ROS mode)


NOTE: users have observed that sometimes it may take a while (10-20 sec) before a sound files "connects"...

NOTE: most of the sound files below are (still) in .wav format; once of these days, I will convert them to .mp3 or .ogg, for your convenience.


[sound clips]      [waterfall spectra]      [mode descriptions]

These are several files with examples of sounds from digital radio modes on short wave.  More info on most of these modes is provided at the bottom of this page.
bullet Hellschreiber (Typenbildfeldfernschreiber)
bullet Feld Hell
bullet Feld-Hell QSO (18 minutes recording of the weekly Sunday euro Hell Net on 3577-3582 kHz at 15:00-15:30 UTC; recorded on 14 sept 2008 by Bill, KA8VIT, via this great web-SDR in The Netherlands)
bullet Hell-72 GL (sorry, poor quality)
bullet Hell-80 (actual QSO with start-stop and synchronous transmissions)
bullet Hell-80 (asychronous mode)
bullet Hell FM-105
bullet Hell FM-245
bullet Hell PSK-105
bullet Hell PSK-245
bullet Hell FSK-105
bullet Hell-FSK-245
bullet C/MT Hell -  text appears in waterfall display
bullet Duplo Hell
bullet Hell-Thomson
bullet FSK (Frequency Shift Keying)
bullet Radio Teletype (RTTY, "ritty")
bullet 170 Hz shift, 45.45 Bd
bullet 170 Hz shift, 50 Bd
bullet 425 Hz shift, 50 Bd
bullet 850 Hz shift, 50 bd
bullet 450 Hz shift, 50 Bd RTTY (Weather synopsis data from station DDK9 (Germany) on 10100 kHz; recorded 5-Apr-2010)
bullet TOR (Telex Over Radio)
bullet PACTOR  R 200 baud PACTOR 2
bullet Amateur PACTOR FEC
bullet Amateur AMTOR ARQ
bullet Amateur AMTOR FEC
bullet Amateur G-TOR;  more info here
bullet Swedish ARQ
bullet SITOR (Simplex Telex Over Radio)
bullet SITOR-A Telex-Over-Radio (SITOR-A = Automatic Repeat Request (ARQ), a.k.a. AMTOR)
bullet SITOR-A Telex-Over-Radio Marker
bullet SITOR-B Telex-Over-Radio (broadcast) (SITOR-B= Forward Error Correction (FEC), a.k.a. NAVTEX)
bullet PACKET  (AX.25) 300 baud and here; more info on this mode here and here
bullet VFT (Voice-Frequency Telegraphy RTTY) (comprises 16 closely packed RTTY signal pairs)
bullet Voice Frequency Telegraphy RTTY
bullet Voice Frequency Telegraphy RTTY (USAF)
bullet PSK
bullet PSK31 clean transmission; more info here, here, and here
bullet BPSK clean transmission
bullet PSK31 - QPSK calling CQ
bullet QPSK31 clean transmission or 1QPSK 15 tone AX25 SABM  packet
bullet FSK31 clean transmission
bullet MT63; more info on this mode is here
bullet clean transmission    (64 tones, 500 Hz or 2 kHz bandwidth)
bullet "quick brown fox" with 500 Hz, with 1000 Hz, and with 2000 Hz
bullet Amateur CLOVER (full duplex)
bullet Morse code "CW" telegraphy
bullet clean transmission 5 WPM, 12 WPM, 17 WPM, 21 WPM
bullet ARRL/W1AW code practice files (various speeds)
bullet Coherent on MS25 and ET 1 calling CQ.
bullet Picture Transmission:
bullet Slow Scan Television (SSTV)  (try 14230 kHz USB)
bullet clean transmission (Scotty1 format)
bullet clean transmission (Martin1 mode)
bullet and here and here
bullet Narrow Band Television (NBTV) - originally from the 1920-1930s, still used today; 10 kHz bandwidth.
bullet sequence of 4 test images
bullet more info on this mode here (UK NBTV net on Saturdays on 3.7 MHz at 08:00 UK time), and here
bullet Weather Facsimile (WEFAX) Weather Map  (from 7878.1 kHz, USB, 120 lines/minute; weather station Offenbach/Germany)
bullet Multi Frequency Shift Keying (MFSK) more info here
bullet MFSK8 the quick brown fox
bullet MFSK16 the quick brown fox, clean transmission, and real QSO
bullet OLIVIA (a spread-spectrum AFSK TOR FEC mode - more info here)
bullet Olivia 125-4
bullet Olivia  250-8
bullet Olivia 500-16
bullet Olivia 1000-32
bullet Olivia 2000-64
bullet Olivia 2000-128
bullet CONTESTIA (4-250)
bullet MT63
bullet MT63-500
bullet MT63-1000
bullet MT63-2000
bullet THROB
bullet Throb-1
bullet Throb-2
bullet Throb-4
bullet ThrobX-1
bullet ThrobX-2
bullet ThrobX-4
bullet Piccolo
bullet RTTYM
bullet DOMINO
bullet DominoEx-4
bullet DominoEx-8
bullet DominoEx-16
bullet JT65A - more info on this mode is here
bullet ROS - more info on this mode is here
bullet ARQ-M2 (Moore Code)
bullet Digital Voice (click here for a presentation by ZS1AN; appears to only work in MS Internet Explorer)
bullet FDMDV
bullet D-STAR   (Digital - Smart Technologies for Amateur Radio)
bullet AOR-DV 
bullet MOTOTRBO  (Motorola Digital Two-Way Radio, compatible with Digital Mobile Radio (DMR) Tier 2 standard)
bullet Weather
bullet Weather Facsimile (recorded on 7878.1 kHz, USB, 120 lines/minute; weather station Offenbach/Germany)
bullet Radioteletype, SYNOP weather report (50 baud, 450 Hz shift)
bullet Aviation, navigation, government, utilities:
bullet Non-Directional Beacon (aviation navigation beacons are in the 190-1750 kHz frequency band (190-1535 kHz in the USA))
bullet DECCA HF Radio Navigation System
bullet LORAN-C Long Range Radio Navigation System
bullet Aircraft Communications Addressing and Reporting System (ACARS)
bullet GMDSS Marine SELCAL System (presumed)
bullet Hyperbolic Radio Navigation System
bullet ICAO Aeronautical SELCAL
bullet DCF77 Time Station Signal
bullet Digital Voice Scrambling (US government/military)
bullet Differential GPS, Minimum Shift Keying
bullet Differential GPS, Quarternary Phase Shift Keying
bullet Link-11 Network (NATO/military)
bullet Over-The-Horizon Radar (OTHR; probably US military)
bullet SELSCAN Link Availability Sounder (presumed)
bullet High-Frequency Active Auroral Research Program (HAARP)
bullet Digital radio broadcasting standard for AM bands, LW/MW/SW
bullet Digital Radio Mondiale (DRM)
bullet DRM IF sample (Radio Luxembourg, 6095 kHz)
bullet Digital Audio Broadcasting (DAB) - primarily used in 175-220 MHz band

Links to pages with sound samples: DM780 (with waterfall images), KB9UKD, EA2BAJ, NB6Z, other

- FFT spectra of the Hell modes are here-

audio spectrum with hellschreiber, MFSK, and RTTY signals
Audio spectrum, left to right: simultaneous Hellschreiber, MFSK, and RTTY signals

Feld Hell


Hell 72 GL (shifted to 900 Hz)


Hell 80 (shifted to 900 Hz)


Hell FM-105


Hell FM-245


Hell PSK-105


Hell PSK-245


Duplo Hell


C/MT Hell


Hell Thomson (shifted to 900 Hz)


RTTY 170 (shifted to 1000 Hz)


RTTY 425 (shifted to 1000 Hz)


RTTY 850 (shifted to 1000 Hz)














Olivia 125-4


Olivia 250-8


Olivia 500-16


Olivia 1000-32


Olivia 2000-64


Olivia 2000-128


















SSTV - Scotty1


Weather Fax




TOR is an acronym for Teleprinting Over Radio. It is traditionally used to describe the three popular "error free" operating modes, AMTOR, PACTOR and G-TOR. The main method for error correction is from a technique called ARQ (automatic repeat request) which is sent by the receiving station to verify any missed data. Since they share the same method of transmission (FSK), they can be economically provided together in one TNC modem and easily operated with any modern radio transceiver. TOR methods that do not use the ARQ hand-shake can be easily operated with readily available software programs for personal computers. For these less complex modes, the TNC (terminal node controller) is replaced by an on-board sound card or out-board audio device. These modes may use redundancy or "human processing" to achieve a level of error correction.

AMTOR is an FSK mode that has been fading into history. While a robust mode, it only has 5 bits (as did its predecessor RTTY) and can not transfer extended ASCII or any binary data. With a set operating rate of 100 baud, it does not effectively compete with the speed and error correction of more modern ARQ modes. The non-ARQ version of this mode is known as FEC, and known as SITOR-B by the Marine Information services.

PACTOR is an FSK mode and is a standard on modern TNCs. It is designed with a combination of packet and Amtor Techniques. It is the most popular ARQ digital mode on amateur HF today. This mode is a major advancement over AMTOR, with its 200 baud operating rate, Huffman compression technique and true binary data transfer capability;
more info here

G-TOR (Golay -TOR) is an FSK mode that offers a fast transfer rate compared to Pactor. It incorporates a data inter-leaving system that assists in minimizing the effects of atmospheric noise and has the ability to fix garbled data. G-tor tries to perform all transmissions at 300 baud but drops to 200 baud if difficulties are encountered and finally to 100 baud. (The protocol that brought back those good photos of Saturn and Jupiter from the Voyager space shots was devised by M.Golay and now adapted for ham radio use.)

PACTOR II is a robust and powerful PSK mode which operates well under varying conditions. It uses strong logic, automatic frequency tracking; it is DSP based and as much as 8 times faster then Pactor. Both PACTOR and PACTOR-2 use the same protocol handshake, making the modes compatible;
more info here

PACTOR-III is a proprietary mode used for message and traffic handling over an HF radio circuit. Use of Pactor-III protocol is limmitted for US hams and some other countries due to the very wide bandwidth of the Pactor-III signal. Presently digital signals that occupy the bandwidth of PCT-III are restricted to a few sub bands:
28.120-28.189 MHz, 24.925-24.930 MHz, 21.090-21.100 MHz, 18.105-18.110 MHz, 14.0950-14.0995 MHz, 14.1005-14.112 MHz, 10.140-10.150 MHz, 7.100-7.105 MHz, or 3.620-3.635 MHz.
Only the embedded hardware (modem) from the German company that owns the rights to this mode, is capable of operating Pactor-III.

CLOVER is a PSK mode which provides a full duplex simulation. It is well suited for HF operation (especially under good conditions), however, there are differences between CLOVER modems. The original modem was named CLOVER-I, the latest DSP based modem is named CLOVER-II. Clovers key characteristics are band-width efficiency with high error-corrected data rates. Clover adapts to conditions by constantly monitoring the received signal. Based on this monitoring, Clover determines the best modulation scheme to use
; more info here

RTTY or "Radio Teletype" is a FSK mode that has been in use longer than any other digital mode (except for morse code). RTTY is a very simple technique which uses a five-bit code to represent all the letters of the alphabet, the numbers, some punctuation and some control characters. At 45 baud (typically) each bit is 1/45.45 seconds long, or 22 msec and corresponds to a typing speed of 60 WPM. There is no error correction provided in RTTY; noise and interference can have a seriously detrimental effect. Despite it's relative disadvantages, RTTY is still popular with die-hard operators
; more info here

PSK31 is the first new digital mode to find popularity on HF bands in many years. It combines the advantages of a simple variable length text code with a narrow bandwidth phase-shift keying (PSK) signal using DSP techniques. This mode is designed for "real time" keyboard operation and at a 31 baud rate is only fast enough to keep up with the typical amateur typist. PSK31 enjoys great popularity on the HF bands today and is presently the standard for live keyboard communications. Most of the ASCII characters are supported. A second version having four (quad) phase shifts (QPSK) is available that provides Forward Error Correction (FEC) at the cost of reduced Signal to Noise ratio. Information on getting started with this mode and other sound card modes is available here .

HF PACKET radio is a FSK mode that is an adaption of the very popular Packet radio used on VHF FM ham radio. Although the HF version of Packet Radio has a much reduced bandwidth due to the noise levels associated with HF operation, it maintains the same protocols and ability to "node" many stations on one frequency. Even with the reduced bandwidth (300 baud rate), this mode is unreliable for general HF ham communications and is mainly used to pass routine traffic and data between areas where VHF repeaters maybe lacking.

HELLSCHREIBER is a method of sending and receiving text using facsimile technology. This mode has been around along time; the recent use of PC sound cards as DSP units has increased the interest in Hellschreiber. The single-tone version (Feld-Hell) is the method of choice for HF operation. It is an on-off keyed system with 122.5 dots/second, or about a 35 WPM text rate, with a narrow bandwidth (about 75 Hz). Text characters are "painted" on the screen, as apposed to being decoded and printed. A new "designer" flavor of this mode called FM HELL has some advantage for providing better quality print, at the expense of a greater duty cycle. As with other "fuzzy modes" it has the advantage of using the "human processor" for error correction.

MT63 is a new DSP based mode for sending keyboard text over paths that experience fading and interference from other signals. It is accomplished by a complex scheme to encode text in a matrix of 64 tones over time and frequency. This overkill method provides a "cushion" of error correction at the receiving end while still providing a 100 WPM rate. The wide bandwidth (1 kHz for the standard method) makes this mode less desirable on crowded ham bands such as 20 meters.
 More info on this 64-tone mode here.

MFSK16 is an advancement to the THROB mode and encodes 16 tones. The PC sound card for DSP uses Fast Fourier Transform technology to decode the ASCII characters, and Constant Phase Frequency Shift Keying to send the coded signal. Continuous Forward Error Correction (FEC) sends all data twice with an interleaving technique to reduce errors from impulse noise and static crashes. A new improved Varicode is used to increase the efficiency of sending extended ASCII characters, making it possible to transfer short data files between stations under fair to good conditions. Similar to SSTV, small images can be transferred (typ. 170x128). The relatively wide bandwidth (316 Hz) for this mode allows higher baud rates (typing is about 42 WPM) and greater immunity to multi path phase shift. This mode is becoming a standard for reliable keyboard-to-keyboard operation and is available in several popular programs.
(more info on this mode here)

THROB is yet another new DSP sound card mode that attempts to use Fast Fourier Transform technology (as used by waterfall displays) to decode a 5 tone signal. The THROB program is an attempt to push DSP into the area where other methods fail because of sensitivity or propagation difficulties and at the same time work at a reasonable speed. There are 1, 2, or 4 throbs per second, resulting in a text speed that is lower than other modes. Check the website of the THROB-author (G3PPT)his web site for the latest developments.
(more info here)

OLIVIA is a new digital MFSK mode and it seems to be highly resistant to QSB (fading) and noise (QRM). It was created in 2005 by Pawel Jalocha (SP9VRC).
Actually, it is a combination of MFSK and Forward Error Correction (FEC that is based on Walsh-functions. As with other modes, Olivia has several variants, each having a different bandwidth (from 500Hz to 2kHz) and different number of tones. Olivia can be very slow (in the order of 2-3 characters per second).  This mode can combine 4-256 tones (2n), with 250, 500, 1000, or 2000 Hz bandwidth. The prevailing standard setting is 32 tones and 1000 Hz with 31.25 baud. This allows ±125 Hz of mis-tuning. Standard frequencies are 7038.5, 14104.5, 14105.5, 14106.5, 14107.5, 14108.5 (calling frequency), 18102.5, 18103.5, 18104.5, 21129.5 kHz (for 1000 Hz AF; USB).

CONTESTIA was derived from OLIVIA by Nick Fedoseev (UT2UZ). It has yet to gain popularity...

Frequency-shift keying (FSK) shifts between two known states. Phase-shift keying (PSK) changes PHASE of a signal against some reference. FSK is sent by either shifting a carrier frequency (F1B) or modulating SSB with two shifting audio tones (AFSK). When sending PSK, a complex audio waveform is transmitted by SSB. Tracking is much more critical for PSK, thus requiring more frequency stability.

DSP (Digital Signal Processing) techniques use high speed processing to convert audio into digital coding, so that a program can manipulate the coded audio in ways not possible with traditional hardware filters. The 16 and 32 bit sound cards found in modern PCs provide this capability.

are those modes that allow the human eye/ear/brain to be used to its maximum potential. In order to do this, a number of rules are required, to ensure that any electronics or logic circuitry is not allowed to make decisions which may be less inspired than human decisions. Examples of potentially Fuzzy modes are Morse Code, HFFAX, SSTV and Hellschreiber. The rules are:
   1) The transmissions must be uncoded. (The signal is sent as a real-time language.)
   2) The receiver must not decide when data is present. (Untouched by any prior decisions.)
   3) The receiver must not decide what data is present. (It must be presented as received.)

The above mode descriptions are taken from NB6Z's web page on digital ham radio.

©2005-2010 F. Dörenberg N4SPP

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