Four definitions
Part 97 names each role precisely, and the questions test the names.
| Term | Definition |
|---|---|
| Telemetry | one-way transmission of measurements at a distance from the measuring instrument |
| Space telecommand station | an amateur station that transmits communications to initiate, modify, or terminate functions of a space station |
| Space station | an amateur station more than 50 km above the Earth |
| Earth station | an amateur station on or near the ground communicating with space stations |
What is the definition of telemetry?
One-way transmission of measurements at a distance from the measuring instrument.
Telemetry is measurements, travelling one way, from something remote. A balloon’s altitude and temperature; a satellite’s battery voltage.
What is a space telecommand station?
An amateur station that transmits communications to initiate, modify, or terminate functions of a space station.
Telemetry comes down; telecommand goes up. One reports, the other controls.
Who may do what
Which amateur stations are eligible to operate as Earth stations?
Any amateur station, subject to the privileges of the class of operator license held by the control operator.
Which amateur stations are eligible to be telecommand stations of space stations, subject to the privileges of the class of operator license held by the control operator of the station?
Any amateur station so designated by the space station licensee
The distinction is worth holding on to. Anyone with the right privileges can be an Earth station — that is just working a satellite. Being a telecommand station means controlling somebody’s spacecraft, so it takes the space station licensee’s designation.
One-way transmissions
Which of the following amateur stations may transmit one-way communications?
A space station, beacon station, or telecommand station.
One-way transmission is normally prohibited — the amateur service is two-way communication. These three are the exceptions, and each has an obvious reason: a satellite must send telemetry, a beacon exists to be heard, and a command uplink has no reply.
Encryption
Which of the following may transmit encrypted messages?
Telecommand signals from a space telecommand station.
The other exception to a firm rule. Obscuring the meaning of a transmission is prohibited throughout the amateur service — but a telecommand link must be authenticated, or anyone could command your spacecraft. Compare E1F09: messages encoded to obscure their meaning are exactly what a mesh network may not carry.
Codes and ciphers are illegal to hide meaning; encryption is legal here to prevent hijacking.
Bands for space stations
Which of the following HF amateur bands include allocations for space stations?
40 meters, 20 meters, 15 meters, and 10 meters.
Which VHF amateur bands have frequencies authorized for space stations?
2 meters.
Which UHF amateur bands have frequencies authorized for space stations?
70 centimeters and 13 centimeters.
Worth memorising as a set, because each question offers plausible near-misses (6 m and 1.25 m are not authorised for space stations; 23 cm is not on the UHF list).
HF: 40, 20, 15, 10. VHF: 2 m only. UHF: 70 cm and 13 cm.
Model craft and balloons
What is the maximum permitted transmitter output power when operating a model craft by telecommand?
1 watt.
What must be posted at the location of a station being operated by telecommand on or within 50 kilometers of the Earth’s surface?
All these choices are correct — a photocopy of the station licence, and a label with the name, address, and telephone number of both the station licensee and the control operator.
Telecommand of a model craft is limited to 1 watt — ample for line-of-sight control, and low enough not to matter to anyone else. And because a telecommand transmitter operates unattended, the licence and contact details must be posted at the station so anyone investigating interference can reach a human.
Which of the following is required in the identification transmissions from a balloon-borne telemetry station?
Call sign.
Telemetry is still an amateur transmission, so it identifies — with your call sign, the same as everything else. This is the rule behind the APRS balloon tracking in the operating module.
Check yourself
- Your friend launches a cubesat and asks you to send it a reset command. What do you need beyond your Extra licence?
- You want to encrypt a message over your local mesh network. May you?
- A beacon transmits continuously with nobody replying. Why is that not a prohibited one-way transmission?
Answers
- Designation by the space station licensee as a telecommand station. Privileges alone are not enough.
- No. Messages encoded to obscure their meaning are prohibited on a mesh network. The encryption exception covers space telecommand only.
- Beacon stations are one of the three explicitly permitted one-way transmitters, alongside space stations and telecommand stations.