Tuesday, August 17, 2010

Remote control and intelligence: telecommand and telemetry

T1A06: What is the FCC Part 97 definition of telecommand?

  1. An instruction bulletin issued by the FCC
  2. A one-way radio transmission of measurements at a distance from the measuring instrument
  3. A one-way transmission to initiate, modify or terminate functions of a device at a distance
  4. An instruction from a VEC

The correct answer is C–A one-way transmission to initiate, modify or terminate functions of a device at a distance.

(Authority: 97.3(a)(43))

T1A07: What is the FCC Part 97 definition of telemetry?

  1. An information bulletin issued by the FCC
  2. A one-way transmission to initiate, modify or terminate functions of a device at a distance
  3. A one-way transmission of measurements at a distance from the measuring instrument
  4. An information bulletin from a VEC

The correct answer is C–A one-way transmission of measurements at a distance from the measuring instrument.

(Authority: 97.3(a)(45))

Many of the questions in the first section of the licensing exams are about regulatory jargon, and these two are no exception. I've combined these two into one post because they're basically opposite sides of the same coin. Both are examples of one-way transmissions. Also, notice that the correct answer to each question is a distractor on the other one; it is therefore important to read the question closely to see which one you got.

Telecommand is what your TV remote does: it sends commands to your TV, causing your TV to "initiate, modify, or terminate functions" based on what button you pushed. Of course, your TV remote is probably infrared (very few television remotes are RF these days), but the principle is the same. Perhaps a better example that almost always uses RF is a garage door opener.

Telemetry is using wireless communication to receive data from a measuring device without a physical connection between the measuring device and the reporting or recording device. If you have a wireless weather station, what that uses to send the gathered data back to the base station is telemetry. The same would apply to a wireless security camera; in this case the data being reported back are the images being captured by the camera.

In the context of amateur radio, telecommand is the use of amateur radio frequencies to remotely control a device. This device can be anything at all, but two specific categories stand out: remote control of model craft (often model airplanes), and remote control of space stations; these two categories receive special treatment within the rules. But nearly anything, even another amateur radio station, may be controlled by telecommand.

One of the most common telemetry activities in amateur radio today are APRS telemetry stations (often called "beacons", which is technically a misnomer, as they're not really beacons, but instead telemetry stations). APRS telemetry stations periodically transmit their location (and possibly other data, such as weather observations, environmental conditions, or anything else the station operator feels like reporting) via a packet data format which may then be received by an APRS digipeater and eventually captured by an APRS gateway and published on the Internet.