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Digital Waterfall

To many, amateur radio is just about two things - either picking up a microphone, or tapping a CW key to communicate with a fellow ham. But there's another rapidly growing segment of the amateur radio community to discover - the world of digital communications.

Prior to about 1982, there was really only one mode of choice, and it involved using a noisy machine called a teletype, but since then radio amateurs have found a use for that other piece of equipment in the shack - the personal computer. Software applications designed to use a PC's sound card have made digital communications easier than ever. Whether you're interested in "chatting" with another ham, want to send and receive email, or transfer information, there's a mode that fits your needs.

This section is designed as an introduction to some of the more popular digital modes. To learn more about a specific one, click on the suggested links below each topic. For further info about digital modes in general, and where to find them on the bands, click on the links below:

Mode Comparison (FLDIGI)
British Amateur Radio Teledata Group
Digital Modes Sights & Sounds (FLDIGI)

ARRL Digital Modes Page
W1AW Digital Bulletin Schedule
Sound Samples (Non-Stop)

High Speed CW (HSCW) Audio Sample
Morse code, the grandfather of all digital modes, is discussed in length on our CW Page, so we won't go into detail about it here, with the exception that CW is in fact a digital mode consisting of elements having unequal lengths, (dots and dashes). High Speed CW (HSCW) is a favorite of hams who operate meteor scatter. By "high speed," we mean speeds that are over 200 words per minute - That's way faster than anyone can copy by ear! The old fashioned way to operate meteor scatter would be to record the bursts on a tape recorder, and then play it back at a much slower speed, in conjunction with high speed memory keyers for transmitting. Today this process is simplified by the use of computers, but many still use tape or digital recorders.  High Speed CW
WinMSDSP Software for HSCW

If you're curious about how HSCW actually works, here's an excellent recording by Jim McMasters (KM5PO), who explains in detail how hams slow down a one-tenth of a second burst to make the CW clear and readable, using the popular MSDSP software.  Click here to download the latest version of MSDSP (for Windows 2000 or newer).

Radioteletype (RTTY) 
Audio Sample

Although Radioteletype, better known as RTTY, is the oldest method of sending keyboard-to-keyboard messages, it remains one of the most popular digital modes. There's no question that new, error-correcting, and bandwidth-efficient modes have captured their share of interest, but RTTY remains the mode of choice for digital contesting and DX'ing. 

The origins of the teletype can be traced to its predecessor, the stock ticker, as far back as the 1870's, and eventually to the teletypewriter (or teleprinter), which emerged around the turn of the twentieth century. The first teleprinter as we know it, was invented by Charles Krum, though it evolved through a series of inventions by a number of other engineers, including Emile Baudot, Frederick G. Creed, Royal Earl House, David Hughes, and Edward Kleinschmidt. Before that time, all telegraph communications had used Morse Code. This, however, required a qualified Morse operator at each end of the circuit, and the data rate was limited to the copying and sending abilities of the individual operators. Teletype offered several commercial advantages over Morse Code -  the most important being automatic copy.

Teletype Machine The standard coding system for teleprinters was originally  the 5-unit Baudot code, (named after its inventor, Emile Baudot). As explained by the Wireless Institute of Australia, "When a key was pressed, the teletype machine would generate a series of pulses by switching a DC voltage on or off. The "on" state was referred to as the "mark" state, and the off condition was called the "space" state" (WIA). The first pulse in the Baudot code was a "start" bit, then five data bits, followed by a "stop" bit, which marked the end of each character. When these pulses reached the receiving machine, they would determine which character was printed. The 5-bit code was later modified by Donald Murray, and the resulting "Murray Code," became the standard code used on commercial teletypes until it was superseded by the ASCII code, which remains the standard today.   

Shortly after World War II, amateur radio operators in the U.S. started to get their hands on obsolete but usable Teletype equipment from commercial operators.

The first two-way radio teletype QSO of record took place in May 1946 between John Evans Williams (W2BFD) of Woodside, Long Island, NY and Dave Winters, (W2AUF) of Brooklyn, NY. These early radio teletype operators used audio frequency shift keying (AFSK), usually on 2 meters, since FSK modulation was not yet authorized by the FCC.

Operation on the HF bands was initially accomplished using “make and break” keying, with the first transcontinental two-way RTTY QSO taking place on 11 meters between W1AW in Newington, CT, and W6PSW in California. While QSO’s could be made using this method, it was quickly realized that FSK was superior. In 1953, after being petitioned by the likes of Merrill Swan (W6AEE) of the RTTY Society of Southern California, and CQ Magazine editor Wayne Green (W2NSD), the FCC investigated and amended part 12 of the Regulations to allow for FSK to be used on the HF bands.

RTTY tape

Teletype over radio relies on FSK, or Frequency Shift Keying of the RF carrier. As mentioned earlier, the teletype machine responds to on-off DC pulses. Over the air, its customary to move the carrier to a different frequency for the "space" signals and back again for the "mark" signals. Carrier shifts of 850 Hz plus or minus 50 Hz was initially specified for amateur radio use by the FCC. Use of this wide shift, however, proved to be troublesome to amateur operators. Commercial operators had already discovered that 100 Hz shifts, commonly called "narrow" shift, worked best on the HF bands, and after a petition to the FCC, Part 12 was amended in 1956 to allow hams to use any shift that was less than 900 Hz (Beishel).

RTTY is a very simple technique that uses a 5-bit code to represent all the letters of the alphabet, the numbers, some punctuation, and 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 words per minute. Although other speeds for sending are allowed, 45 baud has become the most popular for amateur radio. One downside of RTTY, however, is that there is no error correction.

On March 17, 1980, the use of ASCII was approved for use by amateur radio stations, with speeds up to 300 baud (from 3.5 - 21.25 MHz), and 1200 baud (from 28 - 225 MHz). Speeds of 19.2 kilobaud is authorized on frequencies above 420 MHz.

Operating RTTY on FLDIGI

Since the 1980's, teleprinters and Frequency Shift Converters, (which are used to make RTTY function on single side band radios), have been replaced by PC's. Software programs have been written to decode and transmit RTTY messages, and have made the mode accessible to many more operators. Two popular softwares that can decode and send RTTY, using the sound card of your PC, are FLDIGI and MMTTY. For more information about Radioteletype, click on the links below:

Where can I find RTTY Signals?

RTTY signals can be found on all the HF bands, in the "digital mode" segments. A number of different modes are used in these segments, but they can usually be determined by ear. RTTY signals are characterized by a regular shifting back and forth between two tone frequencies. You're most likely to find RTTY activity around these frequencies:

160 METERS 1.800 to 1.810
80 METERS 3.560 (calling) to 3.590
40 METERS 7.080 to 7.100
30 METERS 10.130 to 10.140
20 METERS 14.070 to 14.095
17 METERS 18.100 to 18.105
15 METERS 21.070 to 21.100
12 METERS 24.920 to 24.925
10 METERS 28.070 to 28.150
6 METERS 50.100 to 50.300

Amateur Teleprinting Over Radio (AMTOR) Audio Sample

AMTOR was derived from the commercial SITOR (Simplex Telex Over Radio) system, developed for maritime use in the 1970's. Like its predecessor, RTTY, AMTOR uses a variation of the Baudot Code. It also relies on FSK modulation, but unlike RTTY, it offers a form of error correction. When two AMTOR stations are connected they employ an error detection method called Automatic Repeat Request, (ARQ) - referred to as AMTOR mode A. With this method, three characters are sent at a time, and the receiving station determines if the mark/space ratio is correct. If the received code doesn't match a 4:3 ratio, the receiver assumes an error has occured, and requests that the original data be resent. When AMTOR messages are sent to a group of stations, Forward Error Correction (FEC) - refered to as AMTOR mode B, is the method used. In FEC mode, the transmitting station sends each character twice, and the receiving station checks each one for the correct mark/space ratio. With a set operating rate of 100 baud, and a frequency shift of 170 Hz, AMTOR does not effectively contend with the speed and error correction of the more modern ARQ modes like PACTOR, but it is known for its reliability and performs well even in poor and noisy HF conditions. 

AMTOR QSO using Multipsk software
AMTOR enjoyed widespread popularity from about 1983 through 1991, and is known for its distinctive sound, which is like a rapid series of chirps. According to Steve Ford (WB8IMY), hams made "ample use of its error-free text capability, even setting up automatic AMTOR mailbox operations (MBO's), where messages could be stored for later retrieval from anywhere in the world" (Ford). The mode was originally designed to be used with a Terminal Node Controller (TNC) and it can still be found on most multi mode processors. 

Though not available in a wide variety of softwares, many amateurs make use of programs that utilize a PC sound card. One of the most popular software programs for operating AMTOR (ARQ) is Multipsk, which is freeware, and a good program to receive AMTOR in FEC mode is TrueTTY, developed by DXSoft.

PACTOR Audio Sample

PACTOR is an FSK mode which was developed in Germany by Ulrich Strate (DF4KV), and Hans-Peter Helfert (DL6MAA) for Special Communications Systems GmbH (SCS), and released to the public in 1991. Like its name suggests, PACTOR is an evolution of both AMTOR and Packet Radio, and began as early as 1986 as experiments with AMTOR protocols in an effort to improve performance in noisy HF conditions. PACTOR offers enhanced error correction and a considerably higher 200 baud transfer rate. It is primarily used today for sending and receiving email over the radio.

PACTOR modem When choosing a digital mode to use, its a good idea to weigh the strengths and weaknesses of each type, but also its cost. PACTOR I is an open technology and modems are relatively inexpensive, which has helped it catch on. But the two enhanced modes, PACTOR II and PACTOR III, (both of which are PSK modes), offer much faster data transfer, and have been kept proprietary by the company that developed them. As a result, SCS is the only source for modems capable of operating PACTOR II and III, and the prices of some of these modems - which can be as much $1200.00 - discourage many potential users.  The best resource for information about PACTOR is the SCS website.

Golay Teleprinting Over Radio (GTOR)
G-TOR is a protocol that is nearly three times faster than PACTOR, and incorporates features like Golay forward error correction, full-frame interleaving, on-the-fly Huffman data compression (with run-length encoding), fuzzy acknowledgments (for error tolerance), a long ARQ cycle of 2.4 seconds, and a link-quality based transmission rate. All of these combine to minimize the effects of atmospheric noise while resulting in a mode that is robust and compatible with existing equipment. Kantronics
Kantronics KAM XL

G-TOR uses frequency-shift-keying like PACTOR and Packet radio, but its transmission rate can change depending on band conditions.  While attempting to peform all transmissions at 300 baud, it drops to 200 baud if difficulties are encountered, and to 100 baud if necessary. Frames are sent in normal ASCII or are Huffman and run-length encoded, depending upon which is more efficient on a frame-by-frame basis. The Huffman table for G-TOR is unique, in that unlike PACTOR,  it emphasizes English over German character usage and upper and lower case characters are swapped automatically (frame-by-frame) in a third attempt to compress data. G-TOR transmits either 24, 48, or 72 characters depending on baud rate. Errors are detected at the receiver using a CRC-16 checksum, and depending on how much is missed, it will request a repeat of the last data or parity, or a change in baud rate (Anderson).

G-TOR is a proprietay mode developed by Kantronics, Inc. It was based somewhat on concepts outlined in the MIL-STD-188-100 series of documents, and a protocol devised by M.Golay, that was used by the Voyager space craft to send pictures of Saturn and Jupiter back to Earth. Although it was designed to make use of existing multi-mode TNC hardware, the fact that it is only available from one manufacturer has kept it from gaining widespread popularity. Despite this, however, G-TOR is gaining ground and respect in the world of HF data communications.

The best resource for information about G-TOR is the Kantronics website.

HF Packet 
Audio Sample

HF Packet is an FSK mode that uses the standard AX.25 protocol -  the same one used for VHF Packet Radio. HF Packet, however, uses a 300 baud rate compared to the 1200 baud used on VHF. Although the HF version of packet radio uses a much reduced bandwidth, it still has the ability to "node" many stations on one frequency.

AX.25 - the communications protocol used for Packet radio - was developed in the 1970's and is based on the wired network protocol X.25. Because of the difference in transmitting wirelessly by radio, and because of different addressing schemes, X.25 was modified to suit amateur radio's needs. AX.25 also includes a "digipeater" field to allow other stations to automatically repeat packets to extend the range of transmitters. This practice usually takes place on VHF, where range is limited to line-of-sight.

Packet technology was first developed in the mid-1960', and by the end of the decade was put into practical use in the ARPANET. 
TAPR's  Terminal Node Controller, TNC-1

Initiated in 1970, the ALOHANET, based at the University of Hawaii, became the first large-scale packet radio project. Amateur packet began in Montreal, Canada, with the first transmission occurring on May 31st, 1978.

Packet technology advanced further with the Vancouver Amateur Digital Communication Group's (VADCG) development of a Terminal Node Controller (TNC) in 1980. The current standard for TNC's came about in 1981 at a meeting of the Tuscon Chapter of the IEEE Computer Society. Among the topics discussed was the feasibility of developing a TNC that would be available to amateurs at a modest cost. The Tuscon Amateur Packet Corporation (TAPR) was formed as a result, and on June 26th, 1982, Den Connors (KD2S), and Lyle Johnson, (WA7GXD), made the first packet contact using a TAPR unit. These early prototypes eventually led to the TNC-1, and finally to the TNC-2, (1984-1985), which is now the basis for most packet operations worldwide.
Packet radio has seen a wide variety of uses, ranging from the Packet Bulletin Board System (BBS), which offers the ability to send and receive personal messages, or send and receive messages and bulletins intended for people around the world. Since BBS is part of a national system of other BBSs, it has the ability to pass information to any other BBS in the US or the world.

Other uses include DX Packet Clusters, where amateurs connect to their local cluster to receive reports on the latest DX spotted on the bands. Packet has also been used for transmitting messages via orbiting satelites, and the International Space Station.

One of the most popular uses of Packet Radio of late is the Advanced Packet Reporting System, or APRS.

Invented by Bob Bruninga (WA4APR), APRS is an application that runs "on top of" AX.25. The application utilyzes GPS data to plot a packet station's location on a map. Signals utilizing this mode are found in the 40 and 30 meter bands on HF, as well as on VHF and UHF.

Steve Ford (WB8IMY), writes in a QST article, that "The problem with Packet, as far as HF communication is concerned, is that it requires strong quiet signals at both ends of the path to function efficiently. Packet doesn't tolerate signal fading, noise or interference, which makes it a poor choice for the chaotic world of HF" (Ford). Because of this, Packet is primarily used to pass routine traffic and data between areas where VHF repeaters may be lacking. Still popular with TNC users, there are some software programs available for use with PC sound cards. One of them is the AGWPacket Engine, which came as part of the software suite for many of the Rigblaster products. It can also be downloaded here

CLOVER Audio Sample

CLOVER is a PSK mode, unveiled in 1993 by HAL Communications,  which provides a full duplex simulation. Steve Ford, WB8IMY, wrote in a QST article that CLOVER "was one of the first HF digital modes to use sophisticated data coding, coupled with complex modulation schemes and digital processing technology, in an effort to overcome the vagaries of HF." CLOVER has impressive performance even in the face of weak signals and terrible band conditions. Its key characteristics are bandwidth efficiency with high error-corrected data rates. CLOVER adapts to conditions by constantly monitoring the received signal. Based on this monitoring the program determines the best modulation scheme to use.

Upon its release the initial price tag put CLOVER out of the reach of many hams, dampening interest in the mode, but price reductions and the introduction of CLOVER II has helped it retain a small, yet dedicated following. In order to use CLOVER, you must have a HAL processor, a computer, and a single sideband transceiver.

PSK-31 PSK31

Peter Martinez (G3PLX), who is responsible for adapting the commercial SITOR mode as AMTOR for the amateur radio bands, is credited with inventing PSK31. Over the last decade the mode has been among the most popular of all HF digital modes, especially for keyboard-to-keyboard operating, but that almost wasn't the case. In 2001, Steve Ford, author of the ARRL HF Digital Handbook, wrote that "for a few years, PSK31 languished in obscurity because special DSP hardware was required to use it. But in 1999, Martinez designed a version of PSK31 that needed nothing more than a common sound card" (Ford). To make it even better, the software was made available for free. Shortly thereafter, other programs like DigiPan and WinPSK, made operating PSK31 easier than ever. 

PSK31 combines the advantages of simple variable length text code with a narrow bandwidth phase-shift-keying (PSK) signal using DSP techniques. The standard BPSK mode offers unconnected live keyboard-to-keyboard chat without Forward Error Correction, at a 31 baud rate. Most ASCII characters are supported, with faster sending speeds when using lower case letters. A second version having four (quad) phase shifts, called QPSK is also available.

The chief advantage of using PSK31 is its narrow bandwidth but this isn't achieved naturally. With digital phase modulation, the phase changes abruptly, and without additional measures, wide sidebands would be created. 
PSK31 Sound Card Setup

M. Greenman, offers a good explaination of how this is counteracted, saying "To prevent this, these modes also include 100% raised-cosine amplitude modulation (ASK) at the symbol rate, which reduces the power to zero at the phase range. Because of this, the signal bandwidth is relatively narrow" (Greenman). 

PSK31 is not an error free digital mode, although improved versions such as the PSKR varieties have been developed to improve on its lack of robustness under adverse conditions. PSKR uses a similar design as the MFSK modes, with a convolutional encoder and interleaver, however this comes at the expense of data speed (which is sometimes divided in half when compared to standard BPSK). The PSKR modes are designed for use with data transfer applications such as pskmail, flarq, or other automated-repeat-request applications. 

According to Greenman, "the BPSK modes work well on a quiet, single-hop path, but give poor performance in most other conditions" (Greenman). BPSK31 is the default calling mode, although PSK63F (which does use a form of Forward Error Correction) is also well suited for keyboard-to-keyboard chat. The slower QPSK modes seem most affected by ionospheric doppler phase changes, although Differential PSK helps to maintain sync and reduce the effects of doppler, by allowing the receiver to measure phase difference from symbol to symbol.  

Operating BPSK31 using FLDIGI. Note, the various red lines on the waterfall indicate other stations.

A couple of excellent software programs for PSK31 are FLDIGI and DigiPan

MT63 Audio Sample

MT63 is a new DSP based, keyboard to keyboard, mode that utilizes Walsh 64 bit forward error correcting (FEC), with interleaf of each character every 6.4 seconds. It is operationally similar to RTTY and PSK31, however, the data components are spread over 64 tones, spaced 15.625 Hz apart (1 kHz width), each bipolar phase shift keyed at 10 Hz. Because the information is spread both in time and frequency, time domain interference has little effect. MT63 was invented by a Polish radio amateur, Pawel Jalocha, (SP9VRC), who sought to develop a reliable replacement for RTTY. 

The wide bandwidth of MT63 makes it less desirable on crowded ham bands such as 20 or 80 meters, where the movement has been toward narrow signals like PSK31. Also, the complex modulation scheme brought about issues with getting FCC approval for amateur use. MT63 has, however, become the mode of preference for MARS traffic nets. In a Navy MARS report on the mode, it was concluded that operation was "easy and inexpensive," and that MT63, "especially at 2000Hz, is much faster than AMTOR or Packet FEC" (Navy MARS). 

THROB Audio Sample

THROB is yet another new DSP sound card mode, which uses a possible 9 tones spaced 8 or 16 Hz apart, which gives a bandwidth of 72 or 144 Hz respectively. According to Ernie Mills, (WM2U), the mode has "three transmission speeds, 1, 2 and 4 throbs/sec which gives data rates of 10, 20 and 40 wpm respectively." THROB is an experimental mode written by Lionel Sear, G3PPT, who is active in the development of many small programs for amateur radio use, including a variation of Hellschrieber, called Slowfeld. The THROB program, according to J. Duffy Beishel, (WB8NUT), 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" (Beishel). 

Two excellent soundcard programs that feature THROB are Multipsk and FLDIGI, as well as the program Sear developed for the mode, called THROB 2000.


MFSK-16 Audio Sample
One of the newest amateur digital modes, MFSK 16, was developed by Nino Porcino (IZ8BLY) of Italy. It is somewhat similar to THROB, but has 16 carriers, spaced 15.625Hz apart and operates at 15.626 baud. MFSK 16 occupies about 316 Hz bandwidth with a data rate of 62.5 bps, or about 80 wpm. Ernie Mills (WM2U) explains in an article about the mode, that MFSK 16 has built-in FEC error correction "which reduces the text throughput to about 42 wpm or 31.25 bps" (Mills). According to J. Duffy Beischel (WB8NUT), the wide bandwidth allows for "greater immunity to multi path phase shift," and improved Varicode helps to increase the efficiency of sending extended ASCII characters, "making it possible to transfer short data files between stations under fair to good conditions" (Beischel).

Multi-Frequency Shift Keying can be traced back to the mid 1930's with the development of a system called LMT. A variant called Coqulet came about in the 1950's, as did Kineplex and Piccolo, the later of which, according to Ernie Mills, (WM2U), was used by the British Foreign office. DTMF, which is widely used today with touch tone telephones is also a form of MFSK.

MFSK 16 is quickly becoming the standard for reliable keyboard to keyboard communications, and is available in several popular programs, including IZ8BLY's "Stream" software, FLDIGI, and Mutipsk

Hellschreiber Audio Sample

Hellschreiber is an early facsimile mode invented by Dr. Rudolf Hell in 1929. It is known to have been used by the Germans during World War II, and some receivers were even built by British and American intelligence to intercept communications. The mode, however, seemed to be forgotten about after the war, until it was rediscovered in 1979 by Hans Evers, whose article "The Hellschreiber, A Rediscovery," was published in
Ham Radio magazine. In the article, Evers argues that Hellschreiber, although it existed simultaneously with RTTY, was never fully accepted by the amateur community probably because of the abundance of RTTY machines that flooded the market at low prices after the war.

Unlike the RTTY machine, in which received pulses determine the character to be, the Hellschreiber uses the transmitted pulses to directly write images of characters on paper tape. Thus, according to Hans Evers (PA0CX), "Hellschreiber writing could be considered a type of facsimile, covering seven images per character, with seven elements per line." The Hellschreiber of the World War II Wehrmacht type that Evers used is described as being "somewhat slower than the RTTY machine," producing 2 1/2 characters per second. Nevertheless, he says, "a respectable 25 words per minute is achieved." 

Feld Hell

Steve Ford, author of the ARRL HF Digital Handbook, describes the Hellschreiber as being visual, "That is to say, the signals paint the text on your screen much in the same sense that a television or fax signal paints an image" (Ford). 

Feld-Hell, a variation of Hellschreiber, works by keying a CW transmitter on for every black portion in a text character, and off for every white space. This method has captured the interest of QRP operators since it requires only a simple CW transceiver to be used with sound card software on a PC. Another variation, called Multi-tone Hell, or MT-HELL, creates text images by using different frequencies (or tones), to represent the black and white areas. 

Feld Hell on FLDIGI
Operating Feld Hell using FLDIGI, during the Feld Hell Club net on 40 meters

Where can I find Hell signals? (coutesy of Feld-Hell club)

In general, most Hell activity will take place on the frequencies listed below. As with any ham radio mode, these are suggested frequencies, and its always good practice to listen before transmitting:

160 METERS 1.804
80 METERS 3.574 to 3.584
40 METERS 7.077 to 7.084
30 METERS 10.137 10.144 (Region I)
20 METERS 14.063
17 METERS 18.104
15 METERS 21.074
12 METERS 24.924
10 METERS 28.074
6 METERS 50.286

HF Weather FAX (WeFAX) Audio Sample

Although not an amateur radio mode, many PC soundcard programs that hams use have the ability to receive Weather Fax transmissions. HF Weather Fax is a means of transmitting graphic weather maps and other images via shortwave or HF radio. Maps or pictures are received using a dedicated radio fax receiver (usually on commercial ships), but can also be received using a single sideband receiver connected to an external facsimile recorder or PC equipped with a soundcard interface and application software.

The main source for HF Weather Fax in the U.S. is the National Weather Service, whose fax program prepares high seas weather maps for broadcast via four U.S. Coast Guard (Boston, New Orleans, Pt. Reyes, and Kodiak) and one DOD transmitter site (Honolulu). These broadcasts are prepared by the Marine Prediction Center, Tropical Prediction Center, Honolulu Forecast Office and Anchorage Forecast Office. Limited satellite imagery, sea surface temperature maps and text forecasts are also available.  WEFAX
Wave height prediction received from station NMF in Boston

The International Ice Patrol also broadcasts radio fax charts from Boston sharing the same transmitters. Other stations, in Halifax and Sydney, Nova Scotia can be received on the east coast of the U.S. when band conditions are favorable.

All National Weather Service broadcasts employ a radio fax signal of 120 lines-per-minute (LPM) and an Index-of-Cooperation of 576. These values must be entered into either the fax printer or software program in order for the image to be displayed properly.

HF Weather Fax Schedule
Marine Radiofax Charts
NOAA HF Fax Home
WMJ Marine Products

OLIVIA Audio Sample
OLIVIA is a new digital MFSK mode created in 2005 by Pawel Jalocha (SP9VRC), who also developed MT63. OLIVIA seems highly resistant to fading and noise, and incorporates Forward Error Correction (FEC), based on Walsh functions. As with other modes, OLIVIA has several variants, each having a different bandwidth (from 500Hz to 2 kHz) and different tones. The mode can combine 4-256 tones (2n), with a 250, 500, 1000, or 2000 Hz bandwidth. The prevailing standard setting is 32 tones and 1000 Hz with 31.25 baud. This allows for 125 Hz of mis-tuning.

Where can I find OLIVIA signals?

40 METERS 7038.5
20 METERS 14104.5, 14105.5, 14106.5, 14107.5, 14108.5 (Calling Frequency)
17 METERS 18102.5, 18103.5, 18104.5
15 METERS 21129.5

A new variation, CONTESTIA, is a digital MFSK mode derived from OLVIA by Nick Fedoseev (UT2UZ). One of the best programs that features both of these new modes is FLDIGI

JT65 Sound Icon

JT65 is a digital protocol intended for amateur radio communications with extremely weak signals. The mode debuted as part of the WSJT software suite developed by Nobel Prize winning scientist, Dr. Joe Taylor (K1JT). Designed to optimize Earth-Moon-Earth contacts and meteor scatter on VHF (or UHF), the mode has become popular of late on the HF bands as well. If you're tuning around the weak signal portions of the bands, you may have already come across its strange musical tones of varying pitch and wondered what it was. 

Operating JT65A with Multipsk on 40 meters

JT65 uses precisely timed transmit-received sequences. You transmit for about 1 minute and listen for one minute. Transmission actually begins 1 second after the start of a UTC minute and stops precisely 46.8 seconds later. There is a 1270.5 Hz synchronizing tone, and 64 additional tones. Messages sent via JT65 are compact and efficient. They usually include just the basic information required for a valid contact, such as call signs, grid locators, and signal reports. EME operators may just send "RO," which means "I've copied both calls and my signal report, and your report is...",  "RRR," which means "the QSO is complete," and "73," which means "best regards, end of contact." 

JT65 has three sub-modes known as JT65A, B and C. They are identical except for the spacing between transmitted tone intervals. At the present time, JT65A is generally used on HF and 6 meters, JT65B on 144 and 432 MHz, and JT65C on 1296 MHz. 

Where can I find JT65 signals?

160 METERS  1.838 MHz
80 METERS  3.576 MHz
40 METERS  7.076 MHz  (USA)
40 METERS  7.039 MHz  (Europe)
30 METERS  10.139 MHz
20 METERS  14.076 MHz
15 METERS  21.076 MHz
10 METERS  28.076 MHz


JT9, developed by Joe Taylor K1JT, is intended for MF and HF use, and was introduced in an experimental version of the WSJT software, 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 permit reception of even weaker signals.

FEC in JT9 uses the same strong convolutional code as JT4: constraint length K=32, rate r=1/2, and a zero tail, leading to an encoded message length of (72+31) 2 = 206 information-carrying bits. Modulation is nine-tone frequency-shift keying, 9-FSK at 12000.0/6912 = 1.736 baud. Eight tones are used for data, one for synchronization. Eight data tones means that three data bits are conveyed by each transmitted information symbol. Sixteen symbol intervals are devoted to synchronization, so a transmission requires a total of 206 / 3 + 16 = 85 (rounded up) channel symbols.

The sync symbols are those numbered 1, 2, 5, 10, 16, 23, 33, 35, 51, 52, 55, 60, 66, 73, 83, and 85 in the transmitted sequence. Tone spacing of the 9-FSK modulation for JT9A is equal to the keying rate, 1.736 Hz. The total occupied bandwidth is 9 1.736 = 15.6 Hz.
  • Modulation: 9-FSK
  • Bandwidth: 15.6 hz
  • TX duration: 49 secs.
  • Baud: 1.736
  •  Min SNR:-27db based on 2500hz bandwidth noise
If you ran across this on the radio and were not familiar with the mode you might think it is a birdie in your radio due to the small bandwidth.


Joe Taylor, K1JT, announced on June 29, 2017 the availability of a new mode in the WSJT-X software, called FT8. FT8 stands for "Franke-Taylor design, 8-FSK modulation" and was created by Joe Taylor, K1JT and Steve Franke, K9AN. It is described as being designed for "multi-hop Es where signals may be weak and fading, openings may be short, and you want fast completion of reliable, confirmable QSO's".


According to Taylor, the important characteristics of FT8 are:
  • T/R sequence length: 15 secs.
  • Message length: 75 bits + 12-bit CRC
  • FEC code: LDPC (174,87)
  • Modulation: 8-FSK, keying rate = tone spacing = 5.86 Hz
  • Waveform: Continuous phase, constant envelope
  • Occupied bandwidth: 47 Hz
  • Synchronization: three 7x7 Costas arrays (start, middle, end of TX)
  • Transmission duration: 79*2048/12000 = 13.48 secs.
  • Decoding threshold: -20 dB (perhaps -24 dB with a priori decoding, TBD)
  • Operational behavior: similar to HF usage of JT9, JT65
  • Multi-decoder: finds and decodes all FT8 signals in passband
  • Auto-sequencing after manual start of QSO

Compared to the so called slow modes (JT9, JT65, QRA64), FT8 is a few dB less sensitive but allows completion of QSOs four times faster. Bandwidth is greater than JT9, but about 1/4 of JT65A and less than 1/2 QRA64. Compared with the fast modes (JT9E-H), FT8 is significantly more sensitive, has much smaller bandwidth, uses the vertical waterfall, and offers multi-decoding over the full displayed passband. Features not yet implemented include signal subtraction, two-pass decoding, and use of a priori (already known) information as it accumulates during a QSO."[14]

There are new softwares available which include JT65, JT9, and FT8. Two of the most popular are WSJT and Multipsk. Both can be downloaded from the links below:

The JT65 Communications Protocol
JT65 Frequenciy Info
Multipsk 4.10 Download
WSJT-X Software Download
WSJT Software Download
MAP65 Software Download

JS8 Call

JS8Call combines the robustness of FT8 with a messaging and network protocol layer for weak signal communication on HF, using a keyboard messaging style interface. Although it is a derivative of the WSJT-X application (described above), it has been restructured and redesigned for message passing using a custom FT8 modulation called JS8.


According to Jordan Sherer KN4CRD, “JS8Call is not designed for any specific purpose other than connecting amateur radio operators who are operating under weak signal conditions.” The software is “heavily inspired by WSJT-X, Fldigi, and FSQCall and would not exist without the hard work and dedication of the many developers in the amateur radio community.”

JS8Call is an open-source derivative work licensed under and in accordance with the terms of the GPLv3 license. The source code modifications are public and can be found in the js8call branch of this repository:

Where can I find JS8Call signals?

160 METERS  1.842 MHz
80 METERS    3.578 MHz
40 METERS    7.078 MHz 
30 METERS    10.130 MHz
20 METERS    14.078 MHz
17 METERS   18.104 MHz
15 METERS   21.078 MHz
12 METERS   24.922 MHz
10 METERS   28.078 MHz
6 METERS     50.318 MHz

Slow Scan Television (SSTV)

Slow Scan Television is a method of transmitting medium and high resolution images over the air using standard audio modulation. Most modern SSTV activities are computer based, and are relatively easy to set up. All that is required to join the fun is a radio, a sound card interface, and a PC with SSTV software.

The concept of Slow Scan Television dates back to 1957, when Copthorne MacDonald began experimenting with an electrostatic monitor and a vidicon tube. The FCC legalized SSTV for amateur radio use in 1968, but because of the specialized equipment needed, few took it up. At the time, operating the mode required a scanner or camera, a modem (to create audio tones), and a cathode ray tube with long persistence phosphors, (that would keep an image visible for ten seconds or longer). Many SSTV operators used tubes found in surplus radar equipment.

A Slow Scan Television transmission consists of horizontal lines, scanned left to right, with color components sent seperately one line after another. The color encoding and order of transmission can vary between modes. To create an image, an audio tone is frequency modulated and transmitted (usually as a single sideband signal). The audio signal has a frequency of 1200 Hz for a frame pulse, 1500 Hz for black, and up to 2300 Hz for peak white. Other signals, called synchronization pulses are represented by a frequency lower than the one representing the black level. These are said to be blacker than black, and therefore cannot be seen on the screen.

In the beginning, SSTV images were produced by an 8-second black and white transmission format, but it didn't take long for experimenters to get tired with black and white. Soon, they devised clever ways to send color images using the same equipment. The frame - sequential method involved sending the same picture three times, with a red, green, or blue colored filter placed in front of the camera lens.

The receiving station would take three long-exposure photographs of the screen, also placing red, green and blue filters in front of the film camera's lens at the correct time. John Langner (WB2OSZ) writes in the ARRL Handbook, that this method, "had some drawbacks, as any noise on the band could ruin the image registration (overlay of the frames), and spoil the picture."

Images could then be saved and simultaneously displayed on an ordinary color TV.  (Langner).  The Line-Sequential method remedied this by scanning each line three times, allowing pictures to be received in full color in real time. Early line-sequential modes, such as Wrasse SC-1, used a horizontal sync pulse for each of the color components, but a drawback to this method, according to Langner, "is that if the receiving end gets out of step, it won't know which scan represents which color" (Langner). Robot Research, in an attempt to solve these issues, moved away from the traditional RGB color model with their 1200C modes, using Luminance and Chrominance signals instead. With this method, the first part of each line contains the luminance information, (which is a weighted average of the R, G and B components). The remainder of each line contains the chrominance signals, (which is used to convey the color information of the picture). 1200C is efficient, allowing a 120 line image to be sent in about 12 seconds compared to the usual 24, but picture quality suffers, especially on images with sharp, high-contrast edges. One of the most important advantages of 1200C is its compatibility with older black and white equipment (Langner).

The Martin (M1) and Scottie (S1) modes, which are two of the most popular today, have returned to RGB encoding. Both use a single horizontal sync pulse for each set of RGB scans, and differ only in the timing.

Another innovation, introduced by Robot Research, is Vertical-Interval-Signalling, which is a way of encoding the transmission mode into the vertical sync signal. VIS is composed of a start bit, 7 data bits, an even parity bit, and a stop bit, each 30 ms long. To this day, every new transmission mode has adopted Robot's scheme and has assigned codes to their particular mode. With each mode having a unique VIS code, this allows software programs to automatically select the correct mode when set to automatic receive.

SSTV picture quality can vary widely depending on the mode, and the receiver's ability to detect synchronization pulses. There are a wide variety of standards for picture size. Typically, pictures are 128 lines long and take about eight seconds to send and resolution is around 320 X 240.

Where can I find SSTV signals?

80 METERS  3.735
40 METERS  7.040
20 METERS  14.230
15 METERS  21.340
10 METERS  28.680

Digital Slow Scan Television (Digital SSTV)

The latest evolution in the transmission of high quality images is "Digital SSTV." Although not actually Slow Scan Television, the name seems to have stuck since the mode is used to send pictures in a similar fashion. Popular softwares include DIGTRX and Easypal, which use the DRM platform to send images by file transfer.

The advantage over analogue SSTV, according to Paul Young (G0HWC), is the error correction. "With error correction you get a perfect image IE what is sent is what you receive "(Young). Another program currently under development is KGSTV, which is not compatible with Easypal or DIGTRX. KGSTV works by "mimicking" analog SSTV, but instead of scanning an image line by line, KG scans the image in blocks of 16X16 pixels. 15 scan lines consist of 20 blocks of 16X16 pixels, that during transmission, are compressed and digitally encoded one-by-one. The program allows the use of two types of digital modulation - MSK (2 levels) and MSK (4 levels). Minimum Shift Keying (MSK), is an FSK phase that continues where the frequency deviation is equal to half the signalling rate in baud. The time it takes to send an image depends on the mode chosen. KGSTV also allows compression to be adjusted, which has obvious effects on the quality of images, especially JPEGs.


For more information on Digital SSTV, please click on the links below:

G0HWC Digital SSTV Page
Amateur Radio Visual Software
DIGTRX Download


WSPR, (pronounced "whisper"), stands for Weak Signal Propagation Reporter. It is an open source software tool that uses the transmission mode MEPT-JT, written by Joe Taylor, (K1JT), of Princeton, New Jersey. WSPR is designed for sending and receiving low-power transmissions to test potential propagation paths on the MF and HF bands.

According to, in MEPT transmissions, the "radio becomes a beacon that transmits for just under 2 minutes." Normal transmissions carry a station's call sign, maidenhead grid locator, and transmitter power in dBm. Modulation is by narrow-band FSK. The program is said to be able to detect and decode signals with a signal-to-noise ratio as low as -28 dB in a 2500 Hz bandwidth. A nice feature about WSPR is that "spots can be automatically downloaded to a central database: and results can be shown on a large map."


Dial Frequency (MHz)

TX Frequency (MHz)

1.838000 - 1.838200
3.594000 - 3.594200
5.288600 - 5.288800
7.040000 - 7.040200
10.140100 - 10.140300
14.097000 - 14.097200
18.106000 - 18.106200
21.096000 - 21.096200
24.946000 - 24.946200
28.126000 - 28.126200
50.294400 - 50.294600
144.48990 - 144.49010

Winlink Global Messaging System

Winlink Express is a global radio email client that supports a wide selection of transceivers, TNC's, and multiomde controllers, the soundcard mode WINMOR using the included WINMOR virtual TNC, HF PACTOR, SCS Robust Packet, VHF/UHF AX.25 Packet, and direct telnet to CMS servers or RMS Relay (for amateur radio High Speed Multimedia HSMM, Broadband Hamnet, D-STAR DD mode, internet, and other TCP/IP networks).

Winlink Express

Winlink Express is designed to be easily used by single users with a single call sign but it may also be used to simultaneously send and receive mail with one or two tactical addresses or alternate Winlink accounts. It supports a wide selection of transceivers, TNCs and multimode controllers, the sound card modes WINMOR, Ardop, and VARA using virtual TNCs, HF Pactor, SCS Robust Packet, VHF/UHF AX.25 packet radio, and direct telnet to CMS servers or RMS Relay (for amateur radio High Speed Multimedia [HSMM], Broadband HamNet, D-Star DD mode, internet, and other TCP/IP networks).

Winlink Express is often used as a client for emergency communications. It includes special features for EmComm, such as HTML forms creation and compact, formless content transport, plus a growing library of automatically-updated forms.

Click here to learn more about Winlink.

Works Cited

Amateur Radio "WSPR."  <> 24 December 2011.
Anderson, Phil.  (also Michael Huslig, Glenn Prescott, and Karl Medcaff). "G-TOR Background Research." Kantronics Corporation.  <> 9 March 2011. 
Beischel, J. Duffy. "Digital Modes Information Page." PP 1-4. <>  9 March 2011.
Dorenberg, Frank.  "RTTY - Radio Teletype." Web article, and RTTY tape image.  "Franks Ham Radio." <>
Ford, Steve. "The HF Tower of Babel." QST Magazine. January 2001. PP 50-53. ARRL Publishing. Newington, CT

Greenman, M. "PSK Modes." FL DIGI Help Topics. PP 1-3. <> 9 March 2011.
Langner, John. "Slow-Scan Television." 2003 ARRL Handbook. sec. 12.39. American Radio Relay League. Newington, CT.
McMasters, Jim. "Meteor Scatter." Audio file. <> 9 March 2011.
Mills, Ernie. "Digital World Homepage." Various Topics. <> 9 March 2011. 
Wireless Institute of Australia. "Radioteletype, RTTY."  <>  23 March 2011.


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