Last Updated on April 17, 2026 by John Berry
Why does a signal, transmitted from a transmitter and antenna at one end of a link, arrive at the other end to be captured by an antenna and conveyed to a receiver? What is the basic explanation for this radio transmission?
The simple version
A transmitter causes a current to flow in an antenna wire. That current causes a field to occur around the wire. The field results in the launch of a wave. The wave spreads and propagates to the receiver antenna wire. In the receiver wire, it induces a current. That current is conveyed locally to the receiver.
The slightly more complex version
A local operator using a transmitter impresses information onto a radio-frequency signal. Through a transmission line (feeder), the power from the transmitter drives an alternating current into the transmitting antenna.
I’ve shown the scenario diagrammatically below.
Following Ampère’s Law, this alternating current generates an oscillating magnetic field around the antenna wire.
This changing magnetic field, in turn, generates a changing electric field. These two fields constantly recreate each other, detaching from the antenna to form a self-sustaining electromagnetic wave that radiates outward at the speed of light.
This wave consists of an electric component parallel to the antenna wire and a magnetic component orthogonal to it.
As the wave propagates over many kilometers, it spreads out, and its power density decreases according to the inverse-square law (1/r2).
An infinitesimally small portion of this radiating field eventually reaches the receiving antenna. The oscillating electric field pushes and pulls on the free electrons in the antenna wire, while the oscillating magnetic field induces an electromotive force (Faraday’s Law). Together, these force a small alternating current to flow in the receiving antenna.
By the principles of power transfer, this minute power is conveyed down the feeder to the receiver. Although this received power is typically tens to hundreds of decibels below the original transmitted power, it can be amplified and demodulated. For reception, its amplitude must be above the receiver’s noise threshold. The complete process presents the transmitted information to the receiver operator.