Question E2D04:
What technology is used for real-time tracking of balloons carrying amateur radio transmitters?  

Choices:  
A: FT8  
B: Bandwidth compressed LORAN  
C: APRS  
D: PACTOR III    

Correct Answer is  C: APRS  

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APRS (Automatic Packet Reporting System) is the standard amateur radio system for real-time tracking of moving objects, including high-altitude balloons. A GPS-equipped tracker transmits position/altitude as APRS packets on VHF, which are relayed by digipeaters and IGates to the internet (e.g., aprs.fi) for live mapping.

Why C (APRS) is correct:
- Designed specifically for position, telemetry, and messaging.
- Supports real-time updates via a global network of digipeaters/IGates.
- Commonly used on balloons; packets include latitude, longitude, altitude, and status.

Why the other choices are incorrect:
- A: FT8 — Weak-signal HF mode with 15-second cycles; carries minimal info (call/grid), not suitable for continuous real-time tracking or position beacons.
- B: Bandwidth compressed LORAN — LORAN is a navigation system, not an amateur radio data mode; not used for balloon tracking.
- D: PACTOR III — HF data mode (often Winlink email); proprietary modems, ARQ connections, not a broadcast position-reporting system for public mapping.

Useful facts and “rules of thumb” for APRS:
- North America VHF APRS: $144.390$ MHz FM at $1200$ bps AFSK (Bell 202).
- Some UHF APRS: $9600$ bps FSK on regional frequencies.
- Balloon path settings: keep short or none (e.g., WIDE2-1 or direct) to avoid overloading the network from high altitude.
- Common SSIDs: -11 for balloons/airborne, -9 for mobiles, -7 for HTs (conventions, not rules).
- Typical beaconing: every 1–2 minutes during flight for practical “real-time” tracking.

Summary: APRS is purpose-built and widely deployed for exactly this task—real-time tracking of balloons.