Sideband, by mode
Two rules, and they are different — which is exactly why the pool asks both.
Which mode is normally used when sending RTTY signals via AFSK with an SSB transmitter?
LSB.
What is the standard sideband for JT65, JT9, FT4, or FT8 digital signal when using AFSK?
USB
RTTY uses LSB. The WSJT-X family uses USB. There is no unifying principle; they are separate conventions from separate eras. Get it wrong and your signal appears mirrored in frequency and nobody decodes it.
Where the modes live
| Mode | Location |
|---|---|
| Digital generally, 20 m | 14.070 – 14.100 MHz |
| FT8, 20 m | approximately 14.074 – 14.077 MHz |
| RTTY shift | 170 Hz — the most common amateur HF figure |
The FT8 slice is tiny — 3 kHz carrying dozens of simultaneous signals at 50 Hz each, which is the whole point of the mode’s design.
FT8’s clock requirement
Which of the following is required when using FT8?
Computer time accurate to within approximately 1 second.
FT8 transmits in synchronised 15-second slots and the decoder relies on knowing when each began. More than about a second out and nothing decodes — in either direction, so you appear to be transmitting into a void.
Run NTP. This is the first thing to check when FT8 stops working, and it is routinely the answer.
And the etiquette that follows from the slot structure:
Which of the following is good practice when choosing a transmitting frequency to answer a station calling CQ using FT8?
Find a clear frequency during the alternate time slot to the calling station
Because transmissions alternate, the frequency the caller uses is free while they are receiving. Answering in a clear spot during the opposite slot avoids two stations landing on each other.
Winlink and its protocols
Which of the following describes Winlink?
All these choices are correct — a set of standards and network servers for exchanging email over radio, a system to exchange email between amateur and internet addresses, and a system that provides text messaging over amateur radio.
What is another name for a Winlink Remote Message Server?
Gateway.
What is VARA?
A digital protocol used with Winlink.
VARA and PACTOR are the two ARQ protocols that carry Winlink traffic on HF. Both are connected, point-to-point, error-corrected links.
How do you join a contact between two stations using the PACTOR protocol?
Joining an existing contact is not possible, PACTOR connections are limited to two stations
Unlike a CW or SSB contact, there is nothing to break into. A PACTOR or VARA link is a negotiated connection between exactly two stations.
Which of the following is a way to establish contact with a digital messaging system gateway station?
Transmit a connect message on the station’s published frequency.
Interference on an ARQ link
What symptoms may result from other signals interfering with a PACTOR or VARA transmission?
All these choices are correct — frequent retries or timeouts, long pauses in message transmission, and failure to establish a connection.
All three are the same underlying event: ARQ detecting errors and asking again. Interference does not corrupt the message — the protocol will not deliver corrupt data — it slows the link down and eventually drops it.
AREDN
What is the primary purpose of an Amateur Radio Emergency Data Network (AREDN) mesh network?
To provide high-speed data services during an emergency or community event
The mesh networking from the Technician track, organised as a deployable network: repurposed Wi-Fi hardware on amateur frequencies, self-healing, carrying video, file transfer, and messaging at speeds no HF mode approaches.
When nothing decodes
What could be wrong if you cannot decode an RTTY or other FSK signal even though it is apparently tuned in properly?
All these choices are correct — the mark and space frequencies may be reversed, you may have selected the wrong baud rate, or you may be listening on the wrong sideband.
Three failures with one symptom, and the diagnostic order that resolves them:
- Sideband. LSB for RTTY, USB for the WSJT-X family. Try the other one — it is one click and it fixes this more often than anything else.
- Mark/space reversed. Most software has a “reverse” switch, which is the same fix from the other direction.
- Baud rate and shift. 45.45 baud with 170 Hz shift is standard amateur RTTY.
For FT8 specifically, add a fourth: check the clock.
Check yourself
- You are set up for RTTY on 14.080 MHz and hear signals but decode nothing. First thing to try?
- FT8 shows plenty of signals on the waterfall and decodes none of them. Likely cause?
- Two stations are exchanging a Winlink message via PACTOR. Can you join?
Answers
- The other sideband. RTTY is LSB by convention; if it was left on USB, mark and space are reversed.
- Computer clock more than about a second out. FT8 needs accurate time to locate the 15-second slots.
- No. PACTOR connections are point-to-point; there is no contact to join.