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Last page update: 4 January 2017

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SOUNDS

Below are examples of sounds from digital radio modes on short wave. More info on most of these modes is provided further down on this page. These recordings can be used to test your digi-mode decoding software and to help you to recognize signal types. In the player below, first select the playlist for the mode that you are interested in, then select a track in the playlist that is loaded.

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If you have any problems with the player above, please try the original sounds page. If all else fails, you can access the audio files in this directory. Note: Apple iOS does not support click-to-download (2017). For everything related to Hellschreiber and its modes, see my Hellschreiber website.

Does the waterfall display of your digi-mode software look like the one below, even with your antenna disconnected?

noise

I had this problem up to 8-10 MHz! Here is my 2014 write-up about how I fixed it: Equipment bonding and laptop power-adapter filtering for receiver noise reduction". Other notorious sources of such noise are plasma TVs (your own or from your neighbors), cheap PLCs ("internet via powerline" network adapters), LED and CFL (compact fluorescent) "energy saver" lamps (built-in switching power supply), light dimmers, and even your wireless PC-mouse. The minimum to install is an AC line-filter for your radio equipment and ferrite chokes on all your audio and data cables.

AUDIO SPECTRUM OF VARIOUS MODES

Spectrum

"Waterfall display" audio spectrum, left to right: simultaneous Hellschreiber, MFSK, and RTTY signals


Spectrum

Feld-Hell


Spectrum

Feld-Hell


Spectrum

Hell 72 GL


Spectrum

Hell 80


Spectrum

Hell 80



Spectrum

Hell FM-105


Spectrum

Hell FM-105


Spectrum

Hell FM-245


Spectrum

Hell FM-245


Spectrum

Hell PSK-105


Spectrum

Hell PSK-105


Spectrum

Hell PSK-245


Spectrum

Hell PSK-245


Spectrum

Duplo Hell


Spectrum

Duplo Hell


Spectrum

C/MT Hell


Spectrum

C/MT Hell


Spectrum

Hell Thomson


Spectrum

Hell Thomson

(blue: "space" tone only; yellow: "mark" & "space" during character transmission)


Spectrum

RTTY - 170 Hz shift


Spectrum

RTTY - 170 Hz shift, 45.45 Bd


Spectrum

RTTY - 425 Hz shift


Spectrum

RTTY - 850 Hz shift


Spectrum

DominoEx-4


Spectrum

DominoEx-8


Spectrum

DominoEx-16


Spectrum

MT63-500


Spectrum

MT63-1000


Spectrum

MT63-2000


Spectrum

Olivia 125-4


Spectrum

Olivia 250-8


Spectrum

Olivia 500-16


Spectrum

Olivia 1000-32


Spectrum

Olivia 2000-64


Spectrum

Olivia 2000-128


Spectrum

JT65A


Spectrum

ROS


Spectrum

Throb-2


Spectrum

Throb-4


Spectrum

ThrobX-1


Spectrum

ThrobX-2


Spectrum

ThrobX-4


Spectrum

SSTV - Scotty1


Spectrum

Weather Fax


Spectrum

NBTV


Spectrum

FDMDV


BRIEF DESCRIPTION OF SEVERAL MODES

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


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

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.

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.)

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.

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.

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.

HF PACKET radio is an 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.

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 pixels). 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. It was authored by Lionel Sear, G3PPT. 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.

OLIVIA is a digital MFSK mode that is 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 (on 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...

NOTES: 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.

FUZZY MODES 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:

  • The transmissions must be uncoded - the signal is sent as a real-time language.
  • The receiver must not decide when data is present - untouched by any prior decisions.
  • The receiver must not decide what data is present - must be presented as received.

LINKS TO OTHER WEBSITES WITH RADIO SOUND SAMPLES



External links last checked: October 2015


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©2004-2017 F. Dörenberg, unless stated otherwise. All rights reserved worldwide. No part of this publication may be used without permission from the author.