G2E: Digital Modes – Ham Radio General License Study Guide

G2E covers digital mode operating procedures on the amateur HF bands — the sideband choices, frequency shifts, operating frequencies, protocols, and systems used for data communications including RTTY, FT8, VARA, PACTOR, Winlink, and AREDN.

The exam tests knowledge of which sideband to use for RTTY versus FT8/JT modes via AFSK, the standard RTTY frequency shift, what FT8 requires for computer timing, how to answer a CQ in FT8, where digital modes are found on 20 meters, PACTOR's two-station limit, how to contact a Winlink gateway, what AREDN provides, what Winlink is, the name for a Winlink Remote Message Server, and what to check when an RTTY or FSK signal cannot be decoded.

Digital Mode Sidebands

When using AFSK (audio frequency shift keying) with an SSB transmitter, the choice of sideband determines how the audio tones map to RF frequencies. The General exam tests two specific cases:

RTTY has historically used LSB on HF. The newer weak-signal modes (JT65, JT9, FT4, FT8) standardized on USB. Using the wrong sideband when receiving FSK or AFSK signals causes the mark and space tones to be reversed, making decoding impossible.

RTTY Frequency Shift

RTTY (radioteletype) uses two audio tones — mark and space — to represent binary data. The most common frequency shift for RTTY emissions in the amateur HF bands is 170 Hz. This means the mark and space tones are 170 Hz apart. Other shifts (85 Hz, 425 Hz, 850 Hz) exist but 170 Hz is the standard for amateur HF RTTY.

FT8 Operating

FT8 is a weak-signal digital mode developed by Joe Taylor (K1JT) and Steve Franke (K9AN). It uses a strict time-slot system where transmissions are synchronized to 15-second intervals. Key operating requirements and practices include:

• Computer time accuracy: FT8 requires that your computer's clock be accurate to within approximately 1 second. Without accurate timing, FT8 transmissions will not synchronize with the other station's software and decoding will fail.
• Answering a CQ: When answering a station calling CQ using FT8, find a clear frequency during the alternate time slot to the calling station — not the same time slot. This is how FT8's back-and-forth exchange is designed to work.
• Common frequency on 20 meters: FT8 activity on 20 meters is commonly found approximately 14.074 MHz to 14.077 MHz.

20-Meter Digital Segment

Most digital mode operations on the 20-meter band are found between 14.070 MHz and 14.100 MHz. This segment encompasses RTTY, PSK31, FT8, and other data modes. The FT8 activity cluster sits near 14.074–14.077 MHz within this broader digital segment.

PACTOR and VARA

PACTOR is a robust HF digital protocol designed for point-to-point connections in difficult propagation conditions. An important characteristic of PACTOR is that connections are limited to exactly two stations — you cannot join an existing PACTOR contact. There is no broadcast mode or multi-station access. If you attempt to join, you will disrupt the existing session.

VARA is a digital protocol used with Winlink. It serves a similar purpose to PACTOR (reliable HF and VHF data transfer) but is implemented entirely in software. VARA is not related to EME, direction finding, or DX spotting.

Interference symptoms for PACTOR or VARA transmissions can include frequent retries or timeouts, long pauses in message transmission, and failure to establish a connection between stations — any or all of these may occur depending on the severity of the interference.

Winlink

Winlink is a global radio email system that allows amateur radio operators to send and receive email without internet access at one or both ends of the link. It combines multiple capabilities:

• Wireless email via radio
• Packet radio (VHF and UHF)
• HF band operation using PACTOR, VARA, and other protocols

A Winlink Remote Message Server (RMS) is also called a Gateway. To establish contact with a Winlink RMS gateway station, you transmit a connect message on the station's published frequency. The gateway's frequency and call sign are listed in the Winlink network directory.

AREDN

AREDN stands for Amateur Radio Emergency Data Network. An AREDN mesh network provides high-speed data services during an emergency or community event. Using 802.11-based technology on amateur-allocated microwave frequencies, AREDN networks can deliver IP-based communications (video, voice, data) over distances where commercial infrastructure is unavailable or damaged. It is not an FM repeater system, propagation monitoring tool, or DX spotting network.

Troubleshooting FSK Signals

If you cannot decode an RTTY or other FSK signal even though it appears to be properly tuned in, multiple causes are possible:

• Mark and space frequencies may be reversed — using the wrong sideband reverses the polarity of the tones.
• Wrong baud rate selected — the software must be set to match the sending station's baud rate.
• Wrong sideband — RTTY on HF uses LSB; receiving on USB inverts mark and space.

Any of these three conditions alone can prevent decoding. All three are valid causes of failure, so the correct exam answer is "all these choices are correct."

G2E Practice Questions