How do radio telescopes detect radio waves from stars and galaxies?

Radio telescopes detect faint cosmic radio waves using two primary components: a large antenna and a sensitive radiometer, or radio receiver.1

The most common design is the radio reflector, which utilizes a parabolic antenna to collect and focus incoming radiation onto a small antenna known as the feed. This feed, typically a waveguide horn, transfers the signal to the receiver. To ensure the detection of extremely weak signals, the receiver uses solid-state amplifiers cooled to very low temperatures, which minimizes internal noise.1

Once captured, the signals are processed in several ways:
* Spectroscopy: Signals are divided into thousands of frequency channels to analyze specific atomic or molecular lines.1
* Digital Analysis: Broad-bandwidth signals may be converted into digital form and analyzed using Fourier transforms.1
* Averaging: To isolate faint emissions from background noise, the receiver output is often averaged over extended periods.1

Because cosmic radio sources are exceptionally weak, these telescopes are often massive to maximize sensitivity and are shielded from terrestrial radio interference.1