Definition
A small, low-power radio transmitter carried aloft by a weather balloon as part of a radiosonde, used to send temperature, humidity, and pressure measurements back to a ground receiving station as the balloon rises through the atmosphere.
Plain English
A tiny radio attached to a weather balloon that sends weather readings down to a station on the ground while the balloon climbs.
Context Anchor
Seen in upper-air observation discussions, especially when describing weather balloons and the instruments they carry.
Derivation
‘Milliwatt’ means one-thousandth of a watt — a very small amount of transmitting power. The name signals that this transmitter is deliberately low-powered: it only needs enough strength to reach a nearby ground station, not to broadcast widely.
Why Pilots Care
The temperature, humidity, and pressure data sent down by these transmitters feed into the upper-air charts, winds-aloft forecasts, and weather products pilots use for flight planning.
Grounding Statement
Picture a small weather instrument hanging under a balloon, quietly sending its readings back to the ground by radio as it rises.
Intuition Check
Do not picture a large radio station or aircraft radio. Here, the transmitter is small and very low-power, just strong enough to send weather data back to the ground receiver.
Example Sentence 1
As the weather balloon climbed, its milliwatt radio transmitter sent temperature and humidity readings back to the ground station every few seconds.
Example Sentence 2
Ground stations receive signals from the milliwatt radio transmitter attached to the weather balloon for several hours after launch.