VarAC Guide: HF Digital Chat With the VARA Modem

Most amateurs know FT8 as the mode that works when nothing else does, and it does that job superbly. It is also a mode in which you never really talk to anyone. The exchange is a fixed message of a call sign, a locator and a signal report, repeated at set times. If you miss the conversation, there is another family of programs that lets you chat in real time over HF with typed messages, using error-correcting links. VarAC is one of the best known. This guide describes what VarAC is, what you need to set it up, how to connect your radio, which frequencies are used and how to behave on the air, so that your first calls are smooth and polite.

What VarAC Is

According to its developer, VarAC is a modern HF peer-to-peer real-time chat and emergency communication application for amateur radio operators, built on the VARA protocol. VARA is the modem that does the hard work of modulation, coding and error correction, while VarAC is the user interface: it handles the call, the connection, the text window and the extra functions. The developer states that the program is used by more than 90000 radio amateurs in over 100 countries. It also runs on HF, FM and satellite frequencies, which is unusual for a mode of this kind.

The experience is closer to a chat room than to a contest mode. You send a CQ, another station answers, a link is established, and you type messages to each other in a window. The software confirms each block of data, so if the band fades, the text is repeated until it arrives. That is what we call an ARQ link, or automatic repeat request, and it is also why this kind of mode is so useful for message passing and emergency communication.

How It Differs from FT8 and Other Digital Modes

FT8, FT4 and similar weak-signal modes are designed to decode very faint signals with a fixed format and a rigid time structure. They need an accurate clock, a 15 second cycle and a tolerance for lost transmissions. A connected chat program uses a different design. It trades some sensitivity for flexibility and speed: the link adjusts to the conditions, and the messages can be as long as you wish. The comparison table summarises the main differences, and our overview of digital modes beyond FT8 puts the other modes in context.

None of these modes is the best in every case. VarAC is a good fit when you want to have a ragchew without a microphone, when the band is open enough for a link to hold, or when you need a robust path for short messages.

What You Need

• A licence and a station. A transceiver for the band you will use, an antenna and a feedline in good condition. A clean, linear signal matters more for this mode than extra power.
• A computer and a sound interface. The program uses the audio from your radio, so you need a USB sound interface or a radio with a built-in USB audio codec. Our article on the digital interface, sound cards and ground loops explains how to avoid hum and RF feedback.
• The VARA modem and VarAC. VarAC works with the VARA modem, so install both. Read the terms and the limits of the modem version you use, and check the download page for the supported operating systems and the current version.
• Rig control. The program supports control through CAT, RTS or DTR keying, OmniRig, FLrig and Hamlib, according to the developer. If you already control the radio from a logger, choose the method that does not conflict with it. Our guide to rig control with Hamlib covers the common ways to share the radio between programs.

Setting Up Step by Step

1. Install the modem first. Run the VARA installer, start it once and choose the sound card devices for input and output. Then close it, or leave it to be started by VarAC if that is how you set it up.
2. Install VarAC and enter your call sign. The first-run wizard asks for your call sign and locator. Use your real call sign, because the program transmits it in every frame.
3. Point VarAC at the modem and at the radio. Choose the modem connection, then select the rig control method. Test that the frequency display follows the radio and that PTT keys the transmitter.
4. Set the audio level. Start with the lowest drive that produces your normal output, using a dummy load first. The ALC meter should show little or no movement. A tidy digital signal at modest power is better than a distorted one at full power.
5. Select the bandwidth. The developer lists 500 Hz and 2300 Hz options. The narrower setting is more tolerant of a crowded band and is usually the better choice for a first attempt. The wider setting transfers data faster when the conditions are good.
6. Tune to a calling frequency, listen, and transmit. Always listen first. Use the frequency monitor to see whether there is an ongoing QSO, then send a CQ or answer one.

Frequencies and Band Plans

The developer lists popular calling frequencies for the program, given as the USB dial frequency. They include 14.105 MHz on 20 metres, 21.105 MHz on 15 metres, 28.105 MHz on 10 metres, 7.105 MHz on 40 metres and 3.595 MHz on 80 metres. Additional ones are listed for other bands, including 1.995 MHz on 160 metres, 10.133 MHz on 30 metres, 18.107 MHz on 17 metres and 24.927 MHz on 12 metres, with VHF and UHF entries too. These are suggestions made by the program’s authors, not regulations. Whether you may use a certain frequency or a certain bandwidth depends on your licence class, the rules of your country and the band plan of your IARU region.

The key rule is that amateur frequencies are a shared resource. A narrow chat link can interfere with an existing contact if you start transmitting without listening. Check that the frequency is clear for at least a minute or two, because the other end of a QSO may be too weak for you to hear. If you plan to use a wider bandwidth, make sure it fits within the part of the band reserved for digital modes in your band plan. Our summary of the IARU band plans shows how those segments are organised.

Features Worth Knowing

The developer lists many functions around the basic chat. Some of the most useful are the following.

• CQ calls and beacons. You can call CQ with the protocol and let others know that you are on the frequency.
• The frequency monitor. It shows ongoing QSOs and helps you avoid transmitting on top of someone.
• Typing indicator and message queue. You see when your partner is typing, and you can queue messages.
• Automatic QSY. You can move a conversation up or down the band with one click, which helps in a crowded segment.
• Ping. A quick check of the link before a QSO.
• Logging. Automatic QSO logging in ADIF format, with support for popular loggers.
• File transfer, mail and gateways. The program can send files and images, store messages in a mailbox and pass email through other stations that act as gateways.

Treat the messaging and gateway functions with the same care you would give any station-to-station communication. They are subject to the rules of your licence and your country. In particular, business traffic is generally not allowed on amateur frequencies, and the content of a message must not be obscured. If you want to use the program for emergency practice, our article on Winlink over HF describes another way of passing radio email, and shows how the same VARA modem is used there.

Troubleshooting Common Problems

• The link never starts. Check that the radio is on the frequency you think it is, that the sideband is correct and that the receive audio level reaches the modem at a sensible level. Too much or too little audio both prevent the decode. The modem usually offers a level indicator or a spectrum display, so use it.
• The radio keys but nothing is received. Look at the PTT method. If CAT and an RTS or DTR line are both configured, they can conflict. Pick one method and test it with a dummy load.
• Frequent retries and slow transfers. The band may be noisy or fading. Try the narrow bandwidth, a different band or a quieter time of day, and check that your antenna and feedline are free of local noise. Our guide to finding and killing RF noise in a modern home explains how to track down the usual sources.
• Distorted signal. Reduce the audio drive until the ALC stays quiet. Turn off speech processing and any equalisation that might apply to the digital audio path.
• The computer clock is far off. The mode is less sensitive to it than FT8, but a computer that is minutes out can still cause odd behaviour in logs and in the timing of some functions. Keep the system time synchronised.
• Other programs fight for the sound card. Close music players, video calls and notification sounds, because their audio can leak into your transmitted signal.

Identification and Rules

The rules about identification apply to digital chat as they do to voice. In the United States, for example, 47 CFR 97.119 requires an amateur station to transmit its assigned call sign at the end of each communication and at least every 10 minutes during a communication. Programs that exchange call signs as part of every link normally take care of the identification, but you should confirm how yours does it, and what happens during long transfers or when you leave the station unattended. Other countries have their own rules, and some limit the type of encoding or the use of automatic stations. An unattended beacon or an automatic gateway may need additional conditions.

Good Operating Habits

• Listen before you transmit. This is the most important rule of all.
• Keep your signal clean. Reduce the audio drive and the power until the ALC is quiet. A clean signal gets through at lower power and does not splatter.
• Do not hold the frequency. If you have finished, let others use it. Do not leave the beacon on for hours.
• Be ready to move. If the calling frequency is busy, use the QSY feature and continue elsewhere in the band.
• Use sensible power. A link that needs more power than your usual level is probably a sign that a different band or time would work better.
• Keep your clock and locator accurate. Although the mode does not need the strict timing of FT8, a correct locator and call sign make a better impression and help others find you.

The Bottom Line

VarAC brings real conversation back to HF digital operating. Built on the VARA modem, it offers a connected link with error correction, a chat window, a frequency monitor and a set of practical extras, from automatic QSY to file transfer. To get started you need a clean station, a good sound interface, the VARA modem and a rig control method that suits your setup. Begin with the narrower bandwidth, listen carefully, follow your band plan and identify as your rules require. Do that, and you will find a friendly corner of the bands where a typed chat can take you across the world.

Frequently Asked Questions

What is VarAC?

It is an HF peer-to-peer chat and emergency communication application for radio amateurs. It uses the VARA protocol to establish and maintain error-corrected links.

Do I need the VARA modem to use VarAC?

Yes. VarAC is built for the VARA modem, which performs the modulation and error correction, so both must be installed and configured.

What bandwidth can I choose?

The developer lists 500 Hz and 2300 Hz options. The narrow setting is better for crowded bands, while the wide setting transfers data faster when conditions allow.

Which frequencies are used for VarAC calls?

The developer lists dial frequencies such as 14.105 MHz on 20 metres and 7.105 MHz on 40 metres. These are suggestions, so follow your own band plan and licence conditions.

Is VarAC the same as FT8?

No. FT8 uses a fixed short exchange in timed cycles. VarAC creates a connected link for free text conversation, which is more flexible but needs a workable path.

How often do I need to identify?

That depends on your country. In the United States the rule is at the end of each communication and at least every 10 minutes during one. Check your own regulations.