One mode per path
The WSJT-X family is not a set of alternatives — each mode was designed for one kind of propagation, and the design follows from the path’s characteristics.
| Mode | Designed for | Why |
|---|---|---|
| MSK144 | meteor scatter | very short transmissions, to fit inside a burst |
| Q65 | EME and other very weak paths | long, robust, averaged |
| JT65 | weak-signal work generally | decodes at very low signal-to-noise ratios |
| FT8 | HF and general weak signal | 15-second cycles, high throughput for its sensitivity |
Which of the following digital modes is designed for meteor scatter communications?
MSK144.
A meteor trail lasts a fraction of a second, so MSK144 sends very short, rapidly repeated messages — the opposite design choice from EME, where the path is weak but continuous.
Which of the following digital modes is designed for EME communications?
Q65.
How does Q65 differ from JT65?
Multiple receive cycles are averaged.
Averaging is what buys the extra sensitivity. Noise is random and averages toward zero over repeated cycles; the signal is consistent and does not. It costs time, which an EME path has and a meteor burst does not.
What type of modulation is used by JT65?
Multitone AFSK.
Which of the following is a method for establishing EME contacts?
Time-synchronous transmissions alternating between stations.
Strict alternation on a clock, so both stations know exactly when to listen. Which is why every mode in this family needs an accurate computer clock.
What information replaces signal-to-noise ratio when using the FT8 or FT4 modes in a VHF contest?
Grid square
The exchange is call signs and grid square rather than a signal report — which, for a VHF contact, is more useful information anyway.
APRS
What digital protocol is used by APRS?
AX.25.
The amateur adaptation of the X.25 packet standard, with call signs as addresses.
What type of packet frame is used to transmit APRS beacon data?
Unnumbered Information.
UI frames are connectionless — sent without establishing a link and without acknowledgement. That is exactly right for a beacon: you are broadcasting your position to whoever hears it, and there is nobody in particular to acknowledge.
How do APRS stations relay data?
By packet digipeaters.
What does the packet path WIDE3-1 designate?
Three digipeater hops are requested with one remaining.
The path notation is WIDEn-m: n hops requested, m remaining. Each digipeater decrements the second number and stops relaying when it reaches zero.
WIDE3-1 therefore means a three-hop path with one hop left — two digipeaters have already handled it.
Understanding this matters because excessive hop counts are the main cause of APRS network congestion. WIDE2-2 is the usual courteous setting; WIDE7-7 floods a continent and is universally deprecated.
What technology is used for real-time tracking of balloons carrying amateur radio transmitters?
APRS.
High-altitude balloon tracking is the classic APRS application: a small transmitter, a GPS, and a network of digipeaters and gateways that puts the balloon’s position on a public map in real time.
Check yourself
- You want to work EME on 2 metres. Which mode, and what does it do that JT65 does not?
- Your APRS packet shows a path of WIDE2-2. What does that request?
- Why does APRS use unnumbered information frames?
Answers
- Q65, which averages multiple receive cycles — trading time, which an EME path has, for sensitivity.
- Two digipeater hops, with both still remaining — nothing has relayed it yet.
- A beacon is connectionless broadcast: there is no link to establish and nobody in particular to acknowledge it.