I was looking back through a reader poll that I did some time back and noticed that a post on how to set up a Digital HF Station was pretty high on the interest list so I plan to cover that topic here. I have done quite a lot of digital HF operating over the past couple of years (approximately 4,000 Digital QSOs) and have had a lot of fun doing so. I hope to encourage others to give digital modes a try. I am going to break this post into four parts:

• Why do digital HF?
• What’s needed?
• Digital HF Station setup
• Digital HF operation

My goal for this post will be to introduce you to the digital modes and give a flavor of what is involved in getting set up to use them on the air in the HF bands. For those who decide to set up a Digital HF Station, I would recommend that you obtain a simple text such as the ARRL’s “Get on the Air with HF Digital” which gives a more in-depth explanation of what’s required to get on the air using the digital modes than I can provide here.

Why do digital HF?

Probably the biggest single reason to consider using the digital modes on the HF bands is that they can increase a station’s range without building new antennas and/or increasing output power. The more modern digital modes use narrowband signals along with error management techniques to increase the Signal to Noise (S/N) and error performance of a radio channel. In the extreme, modes like JT65 can be used to receive digital transmissions where the signal is at or below the noise floor! The digital modes on the HF bands present many good DX opportunities for modest digital HF stations. Early in my Amateur Radio career, I completed a DXCC Award using a simple Off-Center Fed Dipole antenna and a 100W transceiver over a period of about 6 months using the digital modes.

Some other reasons to try the digital modes include access to additional stations, a chance to work QSOs for operators who are hearing and/or speech impaired, and the opportunity to try a new mode of operation.

There are many different digital modes and discussing all of them is beyond the scope of this post (a good overview of the more common digital modes may be found here). The good news is that one simple hardware and software arrangement will put you on the air with a station that can do virtually all digital modes. For the beginning operator, I would recommend a focus on the Phase Shift Keyed (PSK) and Radio Teletype (RTTY) modes to begin with. These modes are by far the most commonly used and both provide good performance with a modest station. PSK is a modern mode and is probably the best performing of the digital modes for general purpose 2-way digital communications. RTTY is an older digital mode (one of the first to be used in Amateur Radio) and is still widely used by DXpeditions and in contests as well as for general digital communications.

What is needed?

The first step is to setup a simple SSB phone HF station. One does not need to build a big or complex station for digital HF operations – a 100W transceiver and a dipole or vertical antenna will provide plenty of fun for the digital HF operator. Most digital communications take place using only 25 – 75 watts of power so a 100W transceiver is more than adequate. Digital HF modes also work well using QRP power levels. In addition to a basic SSB HF Station, you will need a Personal Computer (PC) that will run a software program to decode the information in digital signals received by your transceiver and to generate the properly modulated audio signals and key your transceiver to enable you to transmit digital information on the HF bands. Those of you who have used HF modems over dial-up telephone lines to access the internet has already used essentially the same techniques that are used to transmit and receive information using the digital HF modes.

The only differences are 1) an Amateur Radio HF SSB transceiver is used to create the audio path instead of a telephone line, 2) the PC plus a sound card is doing what the dial-up modem did, and 3) you are communicating directly with another Amateur Radio Operator with a similar setup to yours instead of an Internet Service Provider.

A basic laptop or desktop PC running Windows or Mac OS X is all that is required to run a Digital HF station. The PC should be modern enough to run Windows XP or Windows 7/8 or the recent versions of Apple’s Mac OS X. The Linux OS is also a possibility.

Most PCs sold within the last 5 years or so have plenty of computing and storage capacity for this purpose. I would also recommend a PC that has at least two USB ports and some sort of connection to the internet for call sign information lookup and possible spotting network access. You should also ensure that your PC is stable and in good working order before you try to use it to operate your digital station. While the digital modes and the associated software are not particularly demanding of your PC, it will be an essential part of completing digital QSOs and you do not want to begin with an unstable PC that locks up or crashes frequently.

To complete your Digital HF Station, I would recommend the use of an external sound card and a rig control interface cable. While these latter two items are not essential (you can get by with the PC’s internal sound card and no rig control interface), I recommend an external sound card and a rig control interface for several reasons. First, an external sound card makes it easier to set up and adjust audio levels for proper operation (more on this later) and it generally provides a little better performance than a PC’s internal sound card. While not essential, a rig control interface cable will automate important aspects of logging, changing bands, and tuning through the digital sub-bands and is not particularly expensive or complex. I have found both of these additions to be very useful enhancements to a Digital HF Station.

There are many different choices for sound card setups for Amateur Radio use ranging from basic radio interfaces which use the PC’s internal sound card all the way to some very high-end units that support radios with dual receivers and have built-in rig control interfaces. Manufacturers and devices to look at include West Mountain Radio’s RigBlasters, Tigertronics SignaLink USB, US Interface’s Navigator as well as others. For the beginning digital operator, I would recommend the SignaLink USB from Tigertronics.

The SignaLink USB is inexpensive and is available in kits that include the proper radio cable and configuration jumper blocks for many different radios. It is compatible with all of the popular digital software packages and performs well. It is widely available from distributors like Ham Radio Outlet and many digital operators are familiar with it and can provide help in getting you on the air.

For rig control, I would recommend a USB to radio control cable from RT Systems if one is available for your transceiver (this is the same cable that is used to program the radio using RT System’s software) .

These cables provide a connection between your radio and your PC that allows the digital software to read the radio’s frequency, tune the radio within a digital sub-band or change bands. While these features are not strictly necessary for digital operation, I find that they make the operating experience for the beginning Digital Operator simpler and more enjoyable and are well worth the small added expense and effort.

Finally, there is the question of Software. Again there are many choices here. I have used two and can recommend both of them:

• Ham Radio Deluxe (HRD)/DM780
• Fldigi

Both of these packages can support all of the popular digital modes, logging of QSOs and Rig Control for digital operations. HRD is a more complete package that includes a full set of logging capabilities, award tracking, spotting cluster access and integration, rotator controls, etc. Fldigi is more of a digital modem program with basic logging capabilities. There is also a native version of Fldigi for Mac OS X and for Linux (although you can run HRD on a Mac using VMware Fusion or Parallels. Personally, I have mostly used Ham Radio Deluxe/DM780.

Digital HF Station Setup

The first step in setting up your Digital Station is to connect your radio to your PC. The figure below shows the connections which are required (this is the configuration we use for our portable Digital Station)

The exact set of steps required to set up and configure a Digital Station will depend on the specific combination of radio, sound card, PC, and software used. How-to books like ARRL’s “Get on the Air with  HF Digital” are good sources of information on how to perform these steps as are the equipment manufacturers’ websites and manuals. The steps required are not complex or difficult but a little help the first time that you do them can be helpful and seeking assistance from an Elmer who has experience with Digital HF is a good idea. Here are a few general suggestions to keep in mind as you set up your Digital Station:

• If your radio has dedicated “DATA” or “ACC” jacks to connect audio to a sound card, these are usually the best way to go. If you use the microphone and speaker/headphones connections, be sure you disable the speech compressor and audio equalization when operating using the digital modes.
• Pay close attention to the instructions related to the installation of drivers for your sound card and rig control cables as the order of doing these steps can be important. Also, be sure that the sound card associated with your radio is NOT your default sound card for your PC or you may put unintended audio over the air.
• Be sure to adjust you transmit and receive audio levels properly so that your digital station performs well and does not emit spurious signals or splatter on the air when you transmit. Your sound card and digital mode software manuals will explain how to do this.

Digital HF Operation

With the setup steps complete, the fun of Digital HF Operation can begin. Both Ham Radio Deluxe and Fldigi provide many features that make digital mode operation easier. These programs include macro capability that will automate many aspects of most QSOs such as calling CQ, responding to a CQ call from another station, providing station and other information, and closing and logging a completed QSO. It is a good idea to take some time to understand the use of your software’s macro capability and to customize your macros with your call sign, station information, etc.

I would recommend that you begin with the PSK digital mode as it is easy to use, very popular on the HF bands, and will generally perform best. Also, take some time and review the applicable band plan for your country as there are specific sub-bands allocated for digital mode operations. An example of the United States may be found here. The most active areas for PSK traffic in the United States will generally be in these frequency ranges:

HF Band	Frequency Range
160 m	1.838 – 1.848 MHz
80 m	3.580 – 3.590 MHz
40 m	7.035 – 7.045 MHz 7.070 – 7.080 MHz
30 m	10.140 – 10.150 MHz
20 m	14.070 – 14.080 MHz
17 m	18.100 – 18.110 MHz
15 m	21.070 – 21.080 MHz
12 m	24.920 – 24.930 MHz
10 m	28.120 – 28.130 MHz

Common Frequencies for PSK Operation

Finally, take some time and experiment with the IF/Roofing filters and Noise Reduction features on your transceiver if you have them. These features, when used properly, will often reduce errors in receiving weak digital signals or help you to better deal with the negative effects of strong digital signals near your operating frequency.

I am considering a future post to cover digital operations using JT65 and WSPR on the HF bands. These modes operate and very low power and in marginal conditions and can be used to complete QSOs over marginal paths and to measure your station’s performance in real time. Please post a comment on this blog or drop me an email if you are interested in these modes. If there is enough interest, I will provide a post on these topics in the near future.

I hope that this post has helped to spark your interest in operating using the Digital Modes on the HF bands. I hope to work you on the HF bands using a digital mode soon!

– Fred (AB1OC)