With the proliferation of personal computers, digital modes on HF have blossomed. Even the oldest digital mode, CW (continuous wave), can be sent by keyboard and received on a computer screen. Some modern transceivers even display CW on built-in screens and allow keyboard sending without a computer or accessory equipment. The second oldest digital mode, RTTY (radio teletype), is now almost exclusively accomplished by a computer — the old mechanical teletype machines are museum pieces. More recent digital modes, such as PSK, MFSK, JT-65, Olivia, etc., are accomplished exclusively by computer software.
Even if your transceiver will decode and display digital modes, to gain the full enjoyment of the wide range of digital modes, you will need an interface device between your computer sound card and your transceiver. This device will electrically isolate your radio equipment from your computer to prevent stray RF from entering your computer, it will allow you to adjust the audio levels, and it will provide a method for keying your transceiver to transmit.
Typically, decoding and encoding for HF digital modes is done at the audio level. Received audio from the transceiver speaker output is sent to the computer audio input where the software decodes the signal and displays it on the computer screen. Digital audio signals generated by computer software are sent to the transceiver microphone input. Control signals to key the transceiver to transmit come from a computer COM or USB port and become a PTT push-to-talk signal for the transceiver. In some cases you may choose to omit the PTT line and use the VOX in your transceiver for transmit control. Follow your manufacturer’s instructions.
Some popular choices for sound card interfaces are the West Mountain Radio RIGblaster model Nomic, and the MFJ Enterprises model MFJ-1275. Other interface devices include a built-in sound card and often provide improved performance over using your computer’s sound card. Some popular choices are the Tigertronics model SignaLink USB and the Timewave model Navigator. Still other choices have the digital software in the interface device and only use your computer as a keyboard and display. A popular device is the Timewave model PK-232. Older PK-232 models manufactured by AEA are available used at relatively low prices. Here’s some good guidance from Gordon Gibby KX4Z for hooking up a SignaLink device to your transceiver: Digital Connections.
In addition to the sound card interface device, you will need some software on your computer. Your logging program may have some digital modes included. Ham Radio Deluxe has a large number of digital modes included. DX4Win includes CW/PSK-31/RTTY. Many stand-alone programs are also available and are mentioned in the various mode discussions that follow.
An excellent source of HF Digital information is the ARRL publication Get on the Air with HF Digital. This 128-page book provides a step-by-step guide to get you started in HF digital and set up and operate your own digital station. It covers RTTY, PSK31, JT65, MFSK, Olivia, and PACTOR. Published in January 2012, it’s as up to date as you’ll find in a publication about HF Digital. Author Steve Ford, WB8IMY; ISBN 978-0-87259-601-6.
Why do we start a discussion of HF Digital modes by talking about CW (continuous wave)? As you will discover, digital modes are accomplished by manipulating your transmitter carrier amplitude on and off or by shifting it’s frequency or phase. The simplest digital mode is to key your carrier on and off, i.e., CW.
CW is an abbreviation for continuous wave and Morse telegraphy. The on-off keying of a carrier is the oldest method of radio communication. Morse proficiency is no longer required to obtain an amateur radio license, but it is the most popular digital mode on HF today. Learning to receive CW by ear takes practice. Over time many hams increase their receiving speed upwards of 50 WPM (words per minute), though 25 WPM is a good goal for casual operating. Initially you will receive CW by writing it on paper, and as your skill improves, you will begin to copy it “in your head” and only write down occasional notes to recall the conversation. Transceivers today include many aids to enhance CW reception — DSP (digital signal processing), filters, IF shift/width, audio peak/null/contour, pitch, and RIT (receiver incremental tuning). Learning to use these controls will increase your enjoyment of CW.
When receiving conditions are poor, CW is more easily copied than voice modes. In an emergency situation CW could be your only method of communicating, so it’s a good idea to learn Morse code just in case. If you’re a DXer, increasing your CW speed will allow you to copy those DXpeditions who send like speed demons, and you’ll have more confidence that you’ve made a solid QSO.
One popular software program for receiving CW is CwGet. A companion program for CW keyboard sending is CwType. You will need a way to key your transceiver on CW. You will not use your sound card for transmitting, only for receiving. Some interface devices have a CW keying output, some don’t. There are ready-made CW cables available for your COM port or your USB port, or you can build a simple keying circuit from examples on the Internet.
You can use a CW receiving program to increase your speed. Copy the code “in your head” without looking at the screen, then check your accuracy by glancing at the screen for confirmation. Don’t depend entirely on the screen display. Use your ear! The MRX Morse Code software program is a good training tool for receiving and sending CW. Also, there is a software program named RufzXP you can run on your computer to practice receiving callsigns.
Of course, you can always send CW the old fashioned way with a hand key or a bug. Newer transceivers have an electronic keyer built-in or you can purchase a CW keyer accessory. MFJ Enterprises has many models from which to choose such as the MFJ-407D. The advantage of using an electronic keyer rather than your transceiver’s built-in keyer is that you have direct control over the speed, weight, tone and volume rather than hunting through the menus in your transceiver. Whichever method you choose for sending, try to send smoothly, neither too fast or too slow. The operator on the other end will appreciate it!
Radio Teletype, RTTY, is the first data mode other than CW to see widespread use by amateur radio operators. While there are a wide array of commercial standards for RTTY, amateurs have adopted a set of standards for everyday use — Baudot code, 60 WPM (words per minute), 170 Hz shift, and “high tones” — all to be explained below. Baudot is a five data bit teleprinter encoding scheme invented in 1870 that includes only uppercase letters, numbers, punctuation, and some special characters like carriage return and line feed. It continues in widespread use today.
Like CW, digital codes are sent using an on-off keying method accomplished by shifting the transmitter’s frequency. The off condition is called a “space” and the on condition is called a “mark”. The normal resting condition when sending RTTY is mark; that is, you are transmitting a continuous carrier that is the mark. When sending characters, your signal will shift the transmitted frequency between mark and space in specific patterns according to the Baudot code. Listening in your receiver to a RTTY station, you can hear the distinctive pattern of shifting frequency between mark and space.
There are two basic methods of generating RTTY — FSK, frequency shift keying, and AFSK, audio frequency shift keying. Using FSK, your transmitter carrier frequency is shifted by changing the frequency of an oscillator stage. The FSK mark and space input signals to your transceiver are DC voltages supplied by an interface device called a “terminal unit”. The PK-232 mentioned above includes circuits to generate FSK signals. Your computer sound card is not used to transmit FSK RTTY.
Using AFSK, your computer sound card generates a 2125 Hz audio tone for the mark and a 2295 Hz audio tone for the space. The difference between the mark and space tones is 170 Hz, the standard shift. The audio tones are sent to your transceiver microphone input to generate the transmitted carrier that shifts frequency between mark and space when transmitting.
The 2125 and 2295 Hz tones are called “high tones” and are the standard for HF RTTY. (On VHF “low tones” of 1275 and 1445 Hz are the standard.) For AFSK it is customary to use the LSB, lower sideband, setting on your transceiver for AFSK RTTY. The RTTY setting on your transceiver is used when your keying method is FSK instead of AFSK.
Using LSB with a 2125 Hz tone as the mark is the “normal” mode. If instead you use the 2295 Hz tone for the mark with LSB, this is the “reverse” mode. Your RTTY software will have settings for normal and reverse. If you switch your transceiver to USB when using normal AFSK tones, your signal will be “upside down”. Others trying to copy you will see gibberish on their screens. You would need to use the “reverse” setting in your RTTY software to get yourself “right side up” if you use USB. Be careful! Most modern transceivers will automatically switch to USB on 20 meters and up! If you don’t switch back to LSB on these bands and use AFSK in the normal mode, you will be upside down, reversed, and no one will copy you. To avoid these difficulties, operate in LSB mode with normal tones on all bands.
Tuning in RTTY for receiving can be difficult without some type of tuning indicator. While some experts can tune in a signal by ear, most of us will benefit enormously from a tuning aid. One common tuning aid is an X-Y scope. Rather than using an actual oscilloscope as in the past, today’s software will display a representation of an oscilloscope on the screen. When correctly tuned, you will see a pattern with one vertical line and one horizontal line. The lines may appear as ellipses due to noise and phase shifts, but they will appear close to the ideal vertical and horizontal pattern when correctly tuned. The following screen grab shows the X-Y scope display in the MMTTY software program. (More about MMTTY later.) You can see the X-Y pattern.
Also shown is an audio spectrum display with two vertical tuning lines representing the mark and space. As you tune across a RTTY signal, the two mark and space peaks will move across the display. You want to adjust your receive frequency until the two peaks are aligned with the two vertical tuning lines. The spectrum display is useful for initial tuning and the X-Y scope is used for fine tuning. With a signal tuned as shown, you will see the transmitted RTTY text on your screen. Also, when you transmit, you will be on the same frequency as the person you are printing, and he will copy your transmission without the need to retune to find you.
MMTTY is an excellent software program dedicated to RTTY. It can be used as a stand-alone program or integrated with logging programs such as DX4Win. The DM-780 program that comes with Ham Radio Deluxe is another good program for RTTY and other digital modes. There are more than a dozen other software programs available for HF digital. MMTTY is a free program and a good choice for both beginners and experts alike.
RTTY operating tends to congregate on the high end of the CW sub-bands. When selecting a frequency, please avoid stations operating other modes such as PSK, AMTOR or Packet. Those signals sound different from RTTY and are easily avoided.
Common RTTY Frequencies: 1838-1843 kHz, 3580-3600 kHz, 7040-7100 kHz, 10120-10150 kHz, 14080-14099 kHz, 18100-18110 kHz, 21080-21100 kHz, 24910-24930 kHz, 28080-28100 kHz.
RTTY contesting is alive and well. N1MM Logger contesting software includes robust RTTY support.
Possibly the third most popular digital mode on HF is PSK31. The name PSK31 derives from the modulation type, phase shift keying, and the data rate, 31.25 baud. PSK31 transmits uppercase and lowercase letters, punctuation and other characters. The normal practice is to send only lowercase letters because they are transmitted faster than uppercase letters. The PSK31 speed is approximately 50 WPM, which is slower than the 60 WPM of RTTY. Although PSK31 is slower than RTTY, it is more robust in noisy conditions and with weak signals. In fact, you can work stations around the world with a 25 watt PSK31 signal when a RTTY contact would require several hundred watts. The lower power requirement makes it attractive for portable operation and for hams that have antenna restrictions.
Your equipment setup for PSK31 is the same as AFSK RTTY — a computer with software, an interface device, and your transceiver.
Instead of using frequency shift keying like RTTY, PSK31 uses phase shift keying. The most common mode of PSK31 is binary phase shift keying, BPSK31, two phases (like the mark and space of RTTY) and no error correction. Quadrature phase shift keying, QPSK31, uses four phases and has error correction. While all this may be interesting to some, don’t worry about it. Your PSK software will sort it all out.
PSK31 has a very narrow bandwidth, allowing many signals to occupy a small spectrum space. As many as 10 or 15 stations can work within a 3 KHz space. Thus, it is common practice to set your transceiver to one frequency such as 14.070 MHz and then use your software program’s built-in tuning feature to set your operating frequency. The conventional practice for PSK31 is to set your transceiver to USB, upper sideband, (not LSB like for RTTY). With a nominal 3 KHz bandwidth SSB filter this will give you a PSK31 operating range of almost 14.070 MHz to 14.073 MHz. Actually, it’s slightly less because your transceiver attenuates audio signals below about 100 Hz or above about 3 KHz. Some people recommend using a narrow filter in your receiver or a narrow DSP setting and then tuning your transceiver’s dial between 14.070 – 14.073 MHz to receive signals. Both schemes work well.
Since PSK31 has a very narrow bandwidth, it is vulnerable to transmitted audio distortion that will cause poor reception at the receiving station. You want to transmit the cleanest signal possible. One way to do that with a 100 watt transceiver is to set the power level to 100 watts and then to turn down the audio gain so that the power out is around 25 watts or less. Use your mic gain control to turn the power down to about 30 watts and then use the audio gain control on your interface device or in your software program to reduce the power even lower. Operators new to PSK31 will want to blast out at high power to make sure they are heard, but experienced operators know that 10 watts makes for a high quality signal that will work the world. Most PSK31 software will have the ability to measure IMD, inter-modulation distortion, on received signals as a figure of merit. A reading of -30 dB is excellent, -20 dB is good and -10 dB is very poor. Often the stations you work will report your IMD reading; and some PSK31 software will automatically report your IMD number during the QSO. Take heed if you are below -20 dB and turn down your audio gain and power settings. ARRL has published some tips for using PSK31.
Here is a screen grab of the PSK31 window in DX4Win. Received text is in the top pane; transmitted text is in the next pane. Below that is a spectrum waterfall display showing strong signals in yellow and weaker signals in light blue. A right-click of your mouse will select a signal to receive, and your transmit frequency will be set to that frequency. Below the waterfall are buttons to transmit stored messages.
Finding free software for PSK31 is becoming difficult because older programs have not kept up with newer versions of Windows or because their authors have moved on to other projects. A very good program for PSK is DigiPan. This program allows simultaneous decoding of 20 or more signals, rather than looking at one signal at a time. This feature enhances chasing DX or contesting. PSK31 Deluxe has been incorporated into Ham Radio Deluxe as has DM-780. If you have an older computer available for ham radio pursuits, try the older software available on the DX Zone and from WM2U’s PSK31 page.
Here are the common frequencies for PSK: 1838 kHz, 3580 kHz, 7070 kHz, 10142 kHz, 14070 kHz, 18100 kHz, 21070 kHz, 24920 kHz, 28120 kHz.
Another digital mode, JT65, is quite different from PSK31. PSK31 is a “conversational” mode; that is, you can carry on a conversation keyboard to keyboard. JT65 has a completely different structure, making it difficult to have a real conversation. JT65 exchanges 13 character messages. So why are we interested in JT65? This mode is very good at hearing weak signals. In fact, it is used for meteor scatter and moon bounce work where signals are extremely weak. JT65-HF is used on the HF bands.
JT65 was invented by Joe Taylor K1JT, thus the JT designation. It uses 64 tones plus a synchronizing tone, thus the 65. JT65 uses one minute transmit and receive cycles. You transmit for one minute and then receive for one minute, all under software control of course. Both frequency and time stability are very important to this mode. A modern stable transceiver will take care of the frequency stability, but for time stability you need to have your computer time clock set very accurately — accurate to the second. To synchronize your computer time clock in Windows 7, open the Control Panel, click on Date and Time, click on Internet Time, click on Change Settings and select a time server. NIST is a good choice. Save that and you’re ready to go.
Read Joe’s WSJT Home Page for details about JT65. ARRL has some free JT65-HF software. Most hams use JT65-HF software available from IZ4CHL and NW7US. You will use this software with your basic AFSK setup used for other digital modes.
Some common JT65 frequencies are 1,838 kHz, 3,576 kHz, 7,076 kHz, 10,139 kHz, 14,076 kHz, 18,102 kHz, 21,076 kHz, 24,920 kHz, and 28,076 kHz. Please avoid the 10,145 to 10,150 kHz window as JT65 is not compatible with other modes operating in that window.
To use the JT65-HF software, enter your personal information like your callsign, grid square, etc., in the appropriate places and select your sound card input and output settings. The other program default settings should be good enough to get you started. Be sure to lower your transmit power to about 25 watts or lower. You don’t need much power for JT65. Tune to a JT65 frequency and observe the signals. You will soon see a CQ transmission.
When you find a CQ, near the end of the minute double click on the signal and you will begin transmitting at the start of the next minute. After your one-minute transmission look for your callsign in the response from the other station. You have made a successful contact! Log it and watch the text block from the other station for additional information, all within the 13 character limit of course. Remember, JT65 is not a conversational mode. You can initiate your own CQ and look for responses during your receive window time. Your software will automatically keep your one minute windows on the correct time.
The advantage of JT65 is its ability to communicate with very low power and poor antennas, making it a good choice for apartment living or temporary setups. For a good challenge, try Worked All States or DXCC using JT65 and QRP. Visit the Challenge to DX by JT65 for the stats.
Multi-Frequency Shift Keying, MFSK, is similar to RTTY, but rather than the two mark and space tones of RTTY, MFSK uses many more tones. MFSK16 uses 16 tones and is probably the most common MFSK mode found on the ham bands. Again the question is why use so many tones? The answer is accuracy. Using multiple tones, your signal can overcome multipath interference and noise. In fact, it is not unusual to have a coast to coast conversation on 80 meters at night using one watt of transmitted power! That’s the advantage of error correction with MFSK. Some operators report having MFSK QSOs with stations that could not be heard in the receiver because their signals were so weak, but the powerful MFSK software pulled them through.
ARRL transmits its bulletins using MFSK16 every weekday evening as well as using RTTY and BPSK31. See the ARRL Operating Schedule for the details.
MFSK16 uses 16 tones spaced 15.625 Hz apart and sent at 15.625 baud. Because of the encoding scheme, your typing speed will be more than 40 WPM, which makes a good conservational mode for keyboard to keyboard chats. The entire MFSK signal is 316 Hz wide, allowing many signals to operate in a small space. Like RTTY, your signal is transmitting at full power whenever you are keyed, but unlike RTTY, you only need a minimum of power to communicate effectively. Keep your power output around 25 watts or less.
Software is available for MFSK-4, 8, 16, 32, and 64. Ham Radio Deluxe offers multiple MFSK modes. Stand alone software, such as Stream by IZ8BLY is available for MFSK8 and 16 and works with Windows XP (not Windows 7, 8). Another good program with multiple AFSK modes is Fldigi which includes MFSK16 and works well with Windows 7, 8. Read about MFSK here.
OLIVIA, CONTESTIA, HELL, THOR, THROB, DOMINOEX……….
You get the idea….! There are many, many new digital modes out there for you to try; too many to discuss here.
Search the Internet for tutorials and software to try out these modes if you’re up to the challenge!
PACTOR, and its forerunner AMTOR, are a significant departure in two respects from the digital modes already discussed.
First, PACTOR is a burst mode; that is, data is sent in short bursts of information called data blocks. The receiving station responds with an ACK (acknowledgement) to indicate the block of data was received correctly or a NAK (non-acknowledgement) to indicate that there are errors. The transmitting station listens for the response and either sends a new block to an ACK or repeats the previous block to a NAK. This scheme provides a near error free mode suitable for message traffic where accuracy is of prime importance. PACTOR can be used as a conversational mode, though the keyboard speed can be less than other digital modes.
Second, a dedicated PACTOR data controller is required rather than just software and a sound card. PACTOR data controllers are now quite expensive, possibly well over $1,000, because the primary users of PACTOR are commercial operators rather than amateurs. The Timewave PK-232C multimode data controller will operate PACTOR I, but to operate the newer, faster modes PACTOR II and PACTOR III you will need the Special Communications Systems (SCS) data controller, which is quite expensive. Older PK-232 data controllers are available for less money, but they are limited to PACTOR I speed.
Unlike other HF digital modes, you don’t need any dedicated software for PACTOR. All the software needed is included internal to the data controller. You will use terminal software on your computer to provide a keyboard and video monitor to the data controller. If you have an SCS data controller, you can use the software from the SCS download page. For the PK-232 you can use HyperTerminal, which in the past was included with Windows but no longer is part of Windows. You can download HyperTerminal or other terminal emulators from several sources on the Internet.
In addition to the ACK/NAK scheme, PACTOR has a continuous transmission mode called FEC, forward error correction. In the FEC mode each character is transmitted twice and there is no ACK/NAK. This mode is used to call CQ, and while not error free, it is good enough to establish communication. When you respond to a CQ, you are trying to “connect” to the other station and your data controller will use the ACK/NAK scheme. The newer PACTOR II and III data controllers are capable of much higher speeds. When establishing a QSO, the data controllers will negotiate the highest speed possible consistent with band conditions. If you have an older PACTOR I data controller, no problem; the newer data controllers are “backward compatible” and will adjust to your speed.
PACTOR activity occurs on the same frequencies as RTTY. The distinctive sound of PACTOR transmissions makes them easy to identify. While it’s popularity is declining, you will still hear PACTOR QSOs in the evening on 40 and 20 meters.
HF packet radio networks once spanned the USA; however, they are no longer active, owing mostly to the rise of the Internet. Packet radio is alive and well on VHF and UHF in some locations. A discussion of packet radio is more appropriate for those bands.
Would you like to do more with HF Digital modes than just type on a keyboard? How about sending pictures on HF? How about receiving pictures from the International Space Station now orbiting the earth? Slow Scan Television, SSTV, will allow you to do that. Use your same AFSK hardware setup as for other digital modes and use SSTV software like the popular free program MMSSTV http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=4871 or you can use Ham Radio Deluxe http://www.ham-radio-deluxe.com/ software DM-780.
Wait. Before you get too excited about pictures from space, the Amateur Radio on International Space Station, ARISS, transmissions are not on HF. They are on the normal downlink frequency of 145.800 MHz. I mention that here because the hardware and software you need for ARISS SSTV is exactly the same as for HF. Once you have it running on HF, you can use it with another radio for ARISS for pictures from space http://www.spaceflightsoftware.com/ARISS_SSTV/ .
SSTV pictures are static images. They are not motion video. It takes about 2 minutes to transmit one image on HF radio depending on the mode used.
An SSTV signal consists of a constant amplitude audio tone that varies in frequency. Higher tones are for bright areas and low tones are for dark areas. Color is achieved by sending each color (red, green, blue) separately and then combining them using software at the receiver. An SSTV transmission starts with a header signal for calibration and to identify the mode used. It is followed by the horizontal scan lines that make up the image frames. There are different modes for SSTV with Scottie S1 popular in the USA and Martin M1popular in Europe. Your SSTV software will allow you to chose the mode. Faster modes are available, S2 and M2, and are used when conditions are good on HF as well as VHF and UHF. Your SSTV software will usually automatically switch the proper mode for receiving. You select the transmit mode.
When transmitting SSTV, you are transmitting continuously, so the same cautions for RTTY apply here — make sure you do not overheat your transceiver. Turn off your speech processor and do not drive the ALC above the normal region or your signal may be distorted. Also, be careful that you do not overheat your amplifier with a continuous 2 minute transmission at full power. Some amps are not made for that, so you may want to decrease your power to about one-third of full power. Use only enough power to get your picture through. Often 100 watts will be enough.
Popular frequencies for SSTV are 3845 kHz, 7171 kHz, 14230 kHz, 21340 kHz, and 28680 kHz. Set your transceiver to upper sideband USB and use your wide SSB filters.
On SSTV proper operating practices are a little different from other modes. First, listen on an SSTV frequency. If nothing is heard, ask on SSB voice if the frequency is in use. This is HF and propagation may not allow you to hear an ongoing QSO or others could be waiting for a station to start transmitting an SSTV picture. It is quite common to have several operators on frequency in a roundtable sending pictures to all. You can call “CQ SSTV” using SSB voice to connect with someone who wants to operate SSTV if the frequency is clear. Unfortunately, quite often these practices are not used and many stations will transmit SSTV at the same time. It can become chaos.
What type of pictures do you send and where do they come from? Your pictures can be JPG, BMP, PNG, or most any photo format your software will allow. Your SSTV software will import photos and will include an editor for you to customize images. You can get pictures from your digital camera or the Internet or from photo editors like PhotoShop. Some obvious pictures would be of yourself, your equipment, as well as your local area landscapes or attractions. I shouldn’t have to mention it, but never send obscene images and stay away from politics and religion.
Most SSTV software will allow you to prepare a picture of text to send or to use as a transparent “template” to overlay on a photo so you can add your callsign and name to the picture. If using MMSSTV, there is a good tutorial of how to do this on the MM Hamsoft website.
Here is a screen grab of MMSSTV. On the left is a window showing your current picture. Buttons above the image allow you to select received, history, transmitted or template images. On the right is the tuning aid, although if you have contacted your station on SSB voice, you really don’t need the tuning aid because you will be right on frequency when the voice is tuned properly. Under the tuning aid is the logbook information for your contact. If you enter the other station’s callsign in the log, it will appear in the templates. At the bottom are thumbnails of photos you have in your library. In the center are buttons to select the mode, usually Scottie 1 for the USA. MMSSTV has a template editor, photo editing and text editing, as well as many features to automate your SSTV QSOs.
To use MMSSTV, click on Options, click on Setup MMSSTV and enter your settings in the windows. Be sure to enter your callsign and your sound card settings. Most of the default settings are good enough to get you started. Load up some images to your library to get started. Have at least half a dozen to start. You don’t want to be in a QSO and have to send the same image a second time! Enjoy!
This discussion of HF Digital Modes is only an introduction to what is possible. You are encouraged to explore the Internet for the details about the latest software and operating modes. Give it a try! It’s fun!
73, Bert N8NN
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