W3PGA’s Ham Radio Digital Modes

Information Page


Communication technologies that are specifically designed to improve "live" HF keyboard operation can now be achieved which were previously only theories, too complex, or too costly to implement to be practical. Thanks to the generosity of radio amateurs (hams) with programming knowledge, and to the Internet, new and powerful communications tools are available to all hams. The evolution and wide spread use of the Personal Computer that include a digital sound card for Digital Signal Processing (DSP), is allowing radio amateurs to use these tools to develop new modes of digital communication. The distinguishing features of live HF digital operation today are the use of lower power, compact or indoor antennas and courteous operating techniques. This reverses the trend of several years ago. Confusion over band space is the obvious down-side as new and old modes compete for space on the HF bands. Crowding on a single band like 20 meters is partly to blame for this issue. Fortunately, the new modes like MFSK16 are designed to improve performance for a wide range of operating conditions. This should allow for increased amateur radio band usage to relieve crowding and extend contact opportunities as propagation changes to favor different bands. These are really exciting times for all radio amateurs the use and enjoy all these new digital modes! An Overview of Digital HF Radio Operating Modes TOR is an acronym for “Teleprinting Over Radio”. It is traditionally used to describe the three popular "error free" communication modes - AMTOR, PACTOR and G-TOR.

There are a number of software programs one can use to decode/encode digital communications.  One of the most popular is Ham Radio Deluxe , DM-780, PSK31, Digipan and many others.  A digital interface with a sound card built in is best. These devices isolate the radio from the computer and have adjustable sound levels.  Most are available with connecting cables to your transceiver, either USB or audio cable to your computer. Hook it up and get on the air.  Technicians have operating privileges on all the digital portions of the bands. Some interfaces are capable of doing CW so with the right software you can operate CW without learning it.  Of course CW was one of the first digital modes. I use the Tigertronics Signalink USB integrated Sound Card and The AEA PK-232 TNC interfaces connected to my HF rig VHF rig.

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HF Digital Modes 

Most Digital modes you will see are on a waterfall Display from most Software.


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 Terminal Node Controller (TNC) radio 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 the new and less complex digital modes, the TNC is replaced by an on-board sound card in the personal computer. AMTOR is an FSK mode that is hardly used by radio amateurs in the 21st Century. 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 like Pactor. The non-ARQ version of this mode is known as FEC, and known as SITOR-B by the Marine Information services.

To hear what an Amtor signal sounds like, click the icon sound icon


PACTOR is an FSK mode and is a standard on modern Multi-Mode TNCs. It is designed with a combination of packet and Amtor Techniques. Although this mode is also fading in use, it is the most popular ARQ digital mode on amateur HF today and primarily used by amateurs for sending and receiving email over the radio. This mode is a major advancement over AMTOR, with its 200 baud operating rate, Huffman compression technique and true binary data transfer capability. To hear what a Pactor signal sounds like, click the icon sound icon

 To hear what a Pactor signal sounds like, click the icon sound icon

 GTOR Mode:

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.) GTOR is a proprietary mode developed by Kantronics. Because it is only available with Kantronics multi-mode TNCs, it has never gained in popularity and is rarely used by radio amateurs.

To hear what a Gtor signal sounds like, click the icon sound icon


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. As with the original Pactor, it is rarely used by radio amateurs since the development of the new PC based sound card modes. Also, like GTOR, it is a proprietary mode owned by SCS and only available with their line of multi-mode TNC controllers.

To hear what a Pactor2 signal sounds like, click the icon sound icon


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.

To hear what and Clover signal sounds like, click the icon sound icon

 RTTY Mode:

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 ms 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 many radio amateurs. This mode has now been implemented with commonly available PC sound card software. True TTY, Sea TTY CWget  are free shareware programs just plug in a 1/8 jack from your Mic/Line input on your PC and the other end to the headphone jack of your receiver and watch the data stream across your screen.

To hear what an RTTY signal sounds like, click the icon sound icon

 PSK Modes:

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. Since PSK31 was one of the first new digital sound card modes to be developed and introduced, there are numerous programs available that support this mode - most of the programs available as "freeware". PSK 63 and PSK 125 are similar but transmit at a faster baud rate but take up slightly more band with. I recommend FLdigi or MIXw to decode with your sound card.

To hear what a PSK-31 signal sounds like, click the icon sound icon

 Packet Mode:

HF PACKET (300 baud) radio is a FSK mode that is an adaption of the very popular Packet radio used on VHF (1200 baud) FM amateur 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. HF and VHF Packet has recently enjoyed a resurgence in popularity since it is the protocol used by APRS - Automatic Position Reporting System mostly on 2 meter VHF and 30 meter HF.

To hear what an HF Paket signal sounds like, click the icon sound icon


To hear what an FM Paket signal sounds like, click the icon sound icon


HELLSCHREIBER is a method of sending and receiving text using facsimile technology. This mode has been around along time. It was actually developed by Germany prior to World War II! The recent use of PC sound cards as DSP units has increased the interest in Hellschreiber and many programs now support this new...well I mean, old mode. 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. Thus, many different fonts can be used for this mode including some basic graphic characters. A new "designer" flavor of this mode called PSK HELL has some advantage for weak signal conditions. As with other "fuzzy modes" it has the advantage of using the "human processor" for error correction; making it the best overall mode for live HF keyboard communications. Feld-Hell also has the advantage of having a low duty cycle meaning your transmitter will run much cooler with this mode.

To hear what a Hellscriber signal sounds like, click the icon sound icon

 MT63 Mode:

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 (1Khz for the standard method) makes this mode less desirable on crowded ham bands such as 20 meters. A fast PC (166 Mhz or faster) is needed to use all functions of this mode. MT63 is not commonly used by amateurs because of its large bandwidth requirement and the difficulty in tuning in an MT63 transmission.

To hear what a MT63 signal sounds like, click the icon sound icon

 THROB Mode:

THROB is yet another new DSP sound card mode that attempts to use Fast Fourier Transform technology (as used by waterfall displays). THROB is actually based on tone pairs with several characters represented by single tones. It is defined as a "2 of 8 +1 tone" system, or more simply put, it is based on the decode of tone pairs from a palette of 9 tones. 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. The text speed is slower than other modes but the author (G3PPT) has been improving his MFSK (Multiple Frequency Shift Keying) program. Check his web site for the latest developments.


To hear what a Throb signal sounds like, click the icon sound icon

 MFSK 16 Mode:

MFSK16 is 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. The relatively wide bandwidth (316 Hz) for this mode allows faster baud rates (typing is about 42 WPM) and greater immunity to multi path phase shift. A second version called MFSK8 is available with a lower baud rate (8) but greater reliability for DXing when polar phase shift is a major problem. Both versions are available in a nice freeware Windows program created by IZ8BLY.

To hear what a MFSK16 signal sounds like, click the icon sound icon

    OLIVIA Modes:       

Olivia 500/8 QSO screen capture on 20mtrs with FLDigi (Linux ver.)


Common Olivia formats currently in use

Bandwidth and Tones Audio Center Marker (Hz) Baud WPM Decode S/N Ratio (db)
500/16 750 31.25 19.5 -13
500/8 750 62.5 29.3 -11
250/8 625 31.25 14.6 -14
1000/32 1000 31.25 24.4 -12
1000/16 1000 62.5 39.1 -10
500/4 750 125 39.1 -10
125/4 625 31.25 9.8 -15

Olivia is a ham radio digital mode designed to work in difficult (low s/n ratios plus multipath propagation) conditions on HF bands (though it also works as well on VHF/UHF). The signal can be decoded even when it is 10-14 db below the noise floor (i.e. when the amplitude of the noise is slightly over 3 times that of the signal). It can also decode well under other noise, QSB, QRM, flutter (polar path) and auroral conditions. Currently the only other digital modes that match or exceed Olivia in sensitivity are some of the WSJT program modes that include JT65A which are certainly limited in usage and definitely NOT ragchew capable.

It was developed at the end of 2003 by Pawel Jalocha. The first on-the-air tests were performed by two radio amateurs, Fred OH/DK4ZC and Les VK2DSG on the Europe-Australia path in the 20-meter amateur band. The tests proved that the protocol works well and can allow regular intercontinental radio contacts at very low power levels. It therefore lends itself to be an excellent QRP and ragchew mode.

Olivia has many formats some of which are consideredstandard and they all have different characteristics. The formats vary in bandwidth (125,250,500,1000, and 2000hz) and number of tones used (2,4,8,16,32,64,128, or 256). This makes it possible to have 40 different Olivia formats which have different characteristics, speeds, and capabilities. Luckily only a relatively few are commonly used.

The standard Olivia formats (bandwidth/tones) are 125/4, 250/8, 500/16, 1000/32, and 2000/64. However the most commonly used formats in order of use are 500/8, 500/16, 250/8, 1000/32, and 1000/16. This can cause some confusion and problems with so many formats and so many other digital modes. After getting used to the sound and look of Olivia in the waterfall, though, it becomes easier to identify the format when you encounter it. About 98% of all current Olivia HF activity is one of the 7 following configurations : 1000/32, 1000/16, 500/16, 500/8, 250/8, 250/4, and 125/4.


To hear what a Olivia signal sounds like, click the icon sound icon



Contesa is a digital mode directly derived from Olivia but not quite as robust. It is more of a compromise between speed and performance. It was developed by Nick Fedoseev, UT2UZ who is also one of the key developers of the MixW Mult-digital mode software application used by many hams. Contestia sounds almost identical to Olivia, can be configured in as many ways, but has essentially twice the speed.  UT2UZ who is also one of the key developers of the MixW Mult-digital mode software application used by many hams. Contestia sounds almost identical to Olivia, can be configured in as many ways, but has essentially twice the speed. Contesa has 40 formats just like Olivia. The formats vary in bandwidth (125,250,500,1000, and 2000hz) and number of tones used (2,4,8,16,32,64,128, or 256). The most commonly used formats right now seem to be 250/8, 500/16, and 1000/32.

UT2UZ who is also one of the key developers of the MixW Mult-digital mode software application used by many hams. Contestia sounds almost identical to Olivia, can be configured in as many ways, but has essentially twice the speed.

So just how well does Contestia perform under very weak signal conditions. Surprisingly well as it handles QRM, QRN, and QSB very easily. It decodes below the noise level but experience has shown that Olivia still outperforms Contestia depending on which variation of the modes are used. However, Contestia is twice as fast as Olivia on a given variation of each respective mode. It is an excellent weak signal, conversational, QRP, and long distance digital mode. When using it for keyboard to keyboard conversation

Contesa  get it's increased speed by using a smaller symbol block size (32) than Olivia (64) and by a using 6-bit decimal character set rather than 7-bit ASCII set that Olivia does. Because it has a reduced character set and does not print out in both upper and lower case. Some traffic nets might not want to use this mode because it does not support upper and lower case characters and extended characters found in many documents and messages. For normal digital chats that does not pose any problem, but also because of these limitations, Contestia has not seen much use and is more of a novelty mode.

 To hear what a Contesa signal sounds like, click the icon sound icon

FSK441 Mode:  It is important your PC Clock is sycronized with WWV or NIST in these modes

FSK441, introduced in 2001 as the first communications mode included with WSJT, is designed to support communication using streaks of radio-reflecting ionscreated in the ionosphere by the trails of meteors entering the Earth's atmosphere. The bursts of signal created by such trails are commonly referred to as “pings”, due to their characteristic sound. Such pings may be as short as a tenth of a second and carry enough information to complete at least one stage of acontact. FSK441 employs multi-frequency shift keying using four tones, at a data rate of 441 baud. Because of the choice of character codes in the protocol, it isself-synchronizing and does not require an explicit synchronization tone. FSK441 is generally used on the 2-meter and 70-centimeter amateur bands. Contacts may be made at almost any time (that is, a meteor shower is not required to be in progress) at distances of up to 1400 miles (2250 km).When transmitted messages include at least one space, the FSK441 decoding algorithm uses that space character as a syncword for zero-overhead synchronization.

JT65 Digital Mode:

JT6M, introduced in late 2002, is intended for meteor scatter and other ionospheric scattering of signals, and is especially optimized for the 6-meter band. The mode also employs multiple frequency-shift keying, but at 44 tones. One of the tones is a synchronization tone, leaving 43 tones to carry data (one tone per character in the character set,

JT65, developed and released in late 2003, is intended for extremely weak but slowly varying signals, such as those found on troposcatter or Earth-Moon-Earth (EME, or "moonbounce") paths. It can decode signals many decibels below the noise floor in a 2500 Hz band (note that SNR in a 2500 Hz band is approximately 28 dB lower than SNR in a 4 Hz band, which is closer to the channel bandwidth of an individual JT65 tone), and can often allow amateurs to successfully exchange contact information without signals being audible to the human ear. Like the other modes, multiple-frequency shift keying is employed; unlike the other modes, messages are transmitted as atomic units after being compressed and then encoded with a process known as forward error correction (or "FEC"). The FEC adds redundancy to the data, such that all of a message may be successfully recovered even if some bits are not received by the receiver. (The particular code used for JT65 is Reed-Solomon.) Because of this FEC process, messages are either decoded correctly or not decoded at all, with very high probability. After messages are encoded, they are transmitted using MFSK with 65 tones.Operators have also begun using the JT65 mode for contacts on the HF bands, often using QRP (very low transmit power); while the mode was not originally intended for such use, its popularity has resulted in several new features being added to WSJT in order to facilitate HF operation.

JT9, intended for MF and HF use, was introduced in an experimental version of WSJT, known as WSJT-X. It uses the same logical encoding as JT65, but modulates to a 9-FSK signal. With 1-minute transmission intervals, JT9 occupies less than 16 Hz bandwidth. JT9 also has versions designed for longer transmission intervals of 2 minutes, 5 minutes, 10 minutes or 30 minutes. These extended versions take increasingly less bandwidth and allow for more sensitivity on receive.

  Most of these modes can be decoded with a simple audio cable and connection to your sound card and Line out or head phone jack on your receiver. Sound card and cable are for the SW listener, If you wish to Transmit you will need an interface to key the transmitter and get the audio from your computer to the transmitter and audio from the receiver to the PC. I recommend Signalink or Rig blaster. Cat Cable and Cat software required to control your radio. Ham Radio Deluxe does it ALL! And is currently Free to download.  The cables are specific to each radio and you will need a serial interface USB adaptor to connect. The Signalink and Rig Blaster have built in Sound cards and connect thru USB ports and protect and isolate signals.



To hear what a JT65 signal sounds like, click the icon sound icon


JT-65 Common Frequencies
Frequencies Segment/Net name Mode Comments Website
1836-1838 JT65 Digital JT65 in USB  
1838 JT65 Digital USB dial freq. http://groups.google.com/group/jt65-hf
3576 JT65 Digital USB dial freq. http://groups.google.com/group/jt65-hf
7076 JT65 Digital USB dial freq. http://groups.google.com/group/jt65-hf
10138 JT65 Digital USB dial freq. http://groups.google.com/group/jt65-hf
10139-10141 JT65 Digital 10139.0 kHz USB VFO Dial Frequency JT65 JT65A JT65B Calling (signal frequency 10140.27+) http://www.obriensweb.com/bozoguidejt65a.htm
14076 JT65 SSB Calling frequency for JT65 (weak signal)  
14076 JT65 Digital USB dial freq. http://groups.google.com/group/jt65-hf
14076-14078 JT65 Digital 14076.0 kHz USB VFO Dial Frequency. JT65 JT65A JT65B Calling (signal frequency 14077.27+) http://www.obriensweb.com/bozoguidejt65a.htm
18102 JT65 Digital USB dial freq.  
21076 JT65 Digital USB dial freq. http://groups.google.com/group/jt65-hf
24917 JT65 Digital USB dial freq. http://groups.google.com/group/jt65-hf
28076 JT65 Digital USB dial freq. http://groups.google.com/group/jt65-hf
50.276 JT65 Digital Weak Signal Users  


The Predominate USA HF Digital Frequencies Are: Mode USB

10 Meter Band: 28.110 - 28.125 Mhz  28.120 Primary

12 Meter Band: 24.920 - 24.930 Mhz  24.920 Primary

15 Meter Band: 21.060 - 21.080 Mhz 21.070 Primary

 17 Meter Band: 18.100 - 18.110 Mhz  18.120 Primary

20 Meter Band: 14.060 - 14.080 Mhz 14.070 Primary

30 Meter Band: 10.130 - 10.145 Mhz 10.140 Primary

40 Meter Band: 7.030 - 7.080 Mhz 7.035 Primary

80 Meter Band: 3.520 - 3.640 Mhz 3.580 Primary


FM Digital Modes

 Currently FM has three modes in Digital. Yeasu Fusion C4FM, Icom D-Star, Motorola TDMA Type 2.

 To hear what a Yaesu Fusion signal sounds like, click the icon sound icon

 To hear what a Icom D-Star signal sounds like, click the icon sound icon

  To hear what a Motorola TDMA Hytera signal sounds like, click the icon sound icon

HF Digital Modes

Yaesu FUSION and Icom D-Star can be used in HF Frequencies in the Phone Sections of the Band Plan.  You must be aware an HF Digital signal can be more than 12Khz wide and may interfere with near by stations, Be sure your not splattering. Normally HF voice you should try to stay at least 3Khz so be aware of your surroundings.


Free-DV Digital Voice for HF

FreeDV Ham Radio digital voice software

FreeDV is an application for Windows and Linux that allows any HF SSB radio to be used for digital voice mode with a bandwidth of just 1.1 kHz. PC Sound card or USB Sound card work well for connection to Transeiver. Signalink works best as it can decode and encode Digital voice and other Digital modes. It has a circuit which can key the radio to transmit. A cable is required to hook to the accessory port of your transriver and a USB cable to your PC.

Speech is compressed down to 1400 bit/s then modulated onto a 1100 Hz wide QPSK signal which is sent to the Mic input

of a SSB radio.  On receive, the signal is received by the SSB radio, then demodulated and decoded by FreeDV.

• Codec 2 voice coder and FDMDV modem
• 50 baud 14 QPSK voice data
• 1 Center BPSK carrier with 2x power for fast and robust synchronisation.
• 1.125 kHz spectrum bandwidth (half SSB) with 75 Hz carrier spacing
• 1400 bit/s data rate with 1375 bit/s open source Codec 2 voice coding and 25 bit/s text for call sign ID
• No interleaving in time or FEC philosophy resulting in low latency, fast synchronization and quick recovery from fades.
• 44.1 or 48kHz sample rate sound card compatible 

In this video watch when it's switched to analog SSB. The SSB bandwidth is about 3 times that of the digital audio. Also note the diagonal black streaks across the waterfall display. That's fading, probably from two reflections arriving out of phase. The ID on the bottom is coming in during the silent periods between words.

It's Open Source, and using Codec2. See http://freedv.org/

Here is what you need:

  • A SSB receiver or transceiver
  • FreeDV software, download links are below.
  • A Windows, Linux or OSX PC with one (receive only) or two sound cards.
  • Microphone or  Headset
  • A SM1000 Digital Voice Adaptor
  • Cables to connect the SM1000 to your SSB radio

Connecting Your Radio:

Those who don't have a special connection for digital modes can use the normal audio inputs and outputs of your radio. The same cables and hardware that you use for other digital modes that are based on PC programs will work with FreeDV, but you will need a second sound interface for the microphone and speaker connections to the FreeDV program. A USB headset of the sort used by gamers is all you need for the second sound interface.

Configuring Your Radio:

Turn off as much processing as possible. In general noise blankers, DSP band limit filtering and narrow bandpass filters are more likely to hurt than help, while compression, DSP noise or carrier elimination, and voice processing are definitely wrong for Digital modes. FreeDV's HF modem does its own DSP, and in general this is true for other digital programs as well.  You can see the received effect of different settings in the S/N (signal to noise ratio) display of FreeDV. A higher S/N is better.  Drive your transmitter to an average power of about 20% of it's PEP power. There is a 8-12 dB peak-to-average power ratio in our HF modem. Over-driving will reduce the received S/N. More is not better for DV!

Watch FreeDV, the new HF digital audio program for Radio Amateurs. FREE DV Video Demo




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This page was last updated Demcember 2015 (C) N3VBJ

Maintained By Jerry N3VBJ n3vbj1@gmail.com