VarAC
| VarAC | |
|---|---|
| Type | Keyboard chat and messaging program |
| Developed by | Irad Deutsch, 4Z1AC |
| Modem | VARA HF; also VARA FM |
| Cost | Free for licensed amateurs (VARA itself needs a paid key for full speed) |
| In use | |
| Platform | Windows; Linux and macOS through compatibility software such as Wine |
| Connection type | Two-way, error-corrected (ARQ) links between two stations |
| Main features | Calling frequencies, beacons, chat, file transfer, store-and-forward mail |
| Also used for | Emergency communications |
VarAC is a free Windows program for typed, keyboard-to-keyboard conversations over amateur radio, built on the VARA sound-card modem. Written by the Israeli amateur Irad Deutsch, 4Z1AC, and introduced in the early 2020s, it combines the live chatting of older keyboard modes such as PSK31 with VARA's error-free, two-way data links, so that every line of text arrives exactly as typed. Its users describe it as part chat program, part message system, and it has gathered a following both among casual HF operators and in emergency communications groups.
How it works
VarAC is the application; VARA does the radio work. VarAC sends text and files to the VARA modem program running on the same computer, which turns them into audio tones for the transmitter and decodes the other station's signal. VARA uses ARQ (automatic repeat request): the receiving station checks each block of data and asks for any damaged block to be sent again. A VarAC contact is therefore a connected link between two stations, not a broadcast, and text either arrives complete or the link reports a failure. VARA also changes speed during the contact to suit conditions, slowing down when signals fade.
On HF, VarAC normally uses VARA HF in its 500 Hz narrow or 2300 Hz standard width. It can also run over VARA FM on VHF and UHF for local contacts. The free, unregistered version of VARA HF is limited in speed, which is enough for chat; file transfers and longer messages benefit from a registered copy.
Calling frequencies and slots
A connected mode raises a practical problem: how do two operators find each other? VarAC solves it with agreed calling frequencies on the popular bands, published by the VarAC community and built into the program. Stations listen on the calling frequency and send CQ calls or periodic beacons, short automatic transmissions announcing that a station is on the air and reachable. Every VarAC station that hears a beacon adds it to a list of recently heard stations, with its signal strength.
To keep the calling frequency clear, VarAC uses slots, a set of nearby working frequencies. When two stations connect, a request from the program moves them both to a free slot, much as voice operators answer a CQ and then agree to move off a calling frequency. Check the current published frequencies and the band plan before transmitting, and keep VARA signals in the data portions of each band.
Features
- Chat. Two operators type back and forth in real time, and each line is confirmed as received.
- File transfer. Small files and images can be sent over the same error-corrected link.
- VMail. A store-and-forward mail feature leaves a message for a station that is not on the air, either on the operator's own station or with a relay station, which can notify the recipient over the air that mail is waiting.
- Relaying. A message can be passed through a third station that both ends can reach, useful when two stations cannot hear each other directly.
- Email gateway. Individual VarAC stations may run a gateway to internet email, making the system decentralized, unlike Winlink, which relies on its own network of gateways and central servers.
- Emergency mode. A simplified EmComm interface and related settings are provided for emergency operation.
Emergency use
Because it needs no internet and no central infrastructure, VarAC appeals to emergency groups as a way to pass written traffic between stations directly. It is not a replacement for Winlink, which delivers formal email to any address worldwide, or for fldigi's NBEMS tools, which can send a single message to many stations at once. Many groups treat it as one more tool, useful for coordinating between operators and moving short messages and files station to station.
Rules
VARA's protocol is proprietary, and US hams have long debated how readily other amateurs can monitor such signals, as Part 97 requires data modes to use publicly documented techniques. Operators remain responsible for station identification and for keeping their signals within the rules for each band.