radio waves

AM & FM: How Radio Works 

Lately I’ve been thinking about how the things I use every day actually work, and since I listen to a lot of podcasts, you can guess where this post is going: radio. 

In a studio, a microphone converts sound waves from a person’s voice into an electronic audio signal. If this was sent out by itself, it would only travel a few metres in air before it faded out. To get radio waves to travel long kilometres to a receiver, we have to combine it with a “carrier wave”—an electromagnetic wave. 

Electromagnetic waves are made up of oscillating electric and magnetic fields, just like visible light, but radio waves are right down on the lower end of the spectrum, so their wavelengths are very long—around 300 metres. 

(Image Credit: NASA)

Sound information is combined with the wave by altering or modulating the wave’s properties, like changing its amplitude, frequency, or phase. There are two ways to combine the audio signal with the carrier wave: amplitude modulation (AM) or frequency modulation (FM). 

AM radio changes the overall amplitude or strength of the wave, varying its height in order to incorporate the sound information. FM radio works a little differently, because it changes the frequency of the wave rather than the amplitude. The frequency is the number of wavelengths that pass by a given point per second—physically, a high frequency wave would look squashed up, and a low frequency wave would look stretched out. 

(Image Credit: Wikimedia Commons)

Both kinds of waves are susceptible to variations in amplitude as they zoom off through the air, but since FM radio relies on changes in frequency rather than amplitude, these variations don’t matter—they can just be ignored, and so the sound quality is usually super clear. But AM radio relies on the amplitude to convey information, so when the amplitude is varied a bit, this results in interference or static, which will be a familiar idea if you’ve ever listened to AM radio on a rural country road. The upside of AM radio is that it travels much further than FM radio, which is probably why you’re listening to it on that rural country road in the first place. 

So once these radio waves—whether AM or FM—hit a radio receiver, their oscillating fields induce a current in the conductor. The sound information encoded into the waves can be extracted, and converted back to sound waves to grace your ears with your favourite music or talk show. 

(Bonus: if you want to use science to learn more cool science, my fave podcasts are Radiolab, the Infinite Monkey Cage, and Big Picture Science.)

A conceptual illustration of Nikola Tesla’s Trans-Oceanic Global Energy System. [After Wardenclyffe Tower in Shoreham Long Island, NY]; Unfortuneately Nikola Tesla’s Trans-Atlantic wireless telephony, broadcasting, and proof-of-concept demonstrations of wireless power transmissions never fully materialized. Tesla claimed to be developing an Intercontinental form of Super-conductive Wireless Technologies which would be capable of distributing free and limitless power throughout the surface of the entire planet. (1901–1917)

Archaeology without a shovel

Modern archaeologists send radio waves into the earth to find unknown cultural heritage.

Have you ever seen a researcher pushing a cart up and down a hill, or back and forth on a field? Then you might have seen a modern archaeologist at work.

Geophysical methods are becoming more and more common in archaeology.

They make it possible for archaeologists to discovered new pieces of cultural heritage without ruining anything, and also to plan where to focus an excavation before it starts. Read more.

Symphony of the Universe

After my radio astronomy article yesterday, I thought I should expand on the idea of “sound” in space—how, after all, can stars and galaxies make noise? Sound waves only travel through a medium, such as solid, liquid or gas, by making their molecules vibrate and creating a compression wave. When there is no medium, there’s no sound—hence why the near-vacuum of space is almost completely silent. In the 90s, NASA released an album called “Symphonies of the Planets”, but the sounds weren’t exactly of the planets: they were converted from measurements of the interactions of electromagnetic disturbances, such as charged particles in the planets’ magnetospheres or trapped radio waves. Electromagnetic waves, such as radio waves or light, don’t need a medium to travel like sound waves do. They’re composed of both electric and magnetic waves and so they’re self-propagating, because the oscillating electric field creates an oscillating magnetic field which then creates an oscillating electric field and so on, and the continued disturbances keep the wave moving forward. It’s not until they’re captured here on Earth that they’re converted into sound, and we can hear the symphony of the universe.

Astronomy Picture of the Day: January 24th, 2015

Light from Cygnus A 

Explanation:

Celebrating astronomy in this International Year of Light, the detailed image reveals spectacular active galaxy Cygnus A in light across the electromagnetic spectrum. Incorporating X-ray data (blue) from the orbiting Chandra Observatory, Cygnus A is seen to be a prodigious source of high energy x-rays. But it is actually more famous at the low energy end of the electromagnetic spectrum. One of the brightest celestial sources visible to radio telescopes, at 600 million light-years distant Cygnus A is the closest powerful radio galaxy. Radio emission ( red) extends to either side along the same axis for nearly 300,000 light-years powered by jets of relativistic particles emanating from the galaxy’s central supermassive black hole. Hot spots likely mark the ends of the jets impacting surrounding cool, dense material. Confined to yellow hues, optical wavelength data of the galaxy from Hubble and the surrounding field in the Digital Sky Survey complete a remarkable multiwavelength view.

Image Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Radio: NSF/NRAO/AUI/VLA

Hercules A

Hercules A, also known as 3C 348, is an elliptical galaxy located about 2 billion light years away in the constellation Hercules. It is the largest galaxy in the constellation, about 1,000 times more massive than our Milky Way. The black hole at its center is also 1,000 times more massive than the Milky Way’s.

The galaxy is also one of the brightest extragalactic radio sources known. The central black hole emits jets of energetic particles that form lobes of radio emission about 1.5 light years wide. The regions of the plasma jets farther from the galaxy show ring-like structures, indicating that the black hole has emitted multiple jets in the past. Regions closer to the galaxy are moving so quickly that relativistic effects beam the light away from us, obscuring those portions of the lobes.

Image from National Geographic, information from NASA.

(NASA)  Together, the radio lobes of Fornax A span over one million light years – what caused them? In the center is a large but peculiar elliptical galaxy dubbed NGC 1316. Detailed inspection of the NGC 1316 system indicates that it began absorbing a small neighboring galaxy about 100 million years ago. Gas from the galactic collision has fallen inward toward the massive central black hole, with friction heating the gas to 10 million degrees. For reasons not yet well understood, two oppositely pointed fast moving jets of particles then developed, eventually smashing into the ambient material on either side of the giant elliptical galaxy. The result is a huge reservoir of hot gas that emits radio waves, observed as the orange (false-color) radio lobes in the above image. The radio image is superposed on an optical survey image of the same part of the sky. Strange patterns in the radio lobes likely indicate slight changes in the directions of the jets.

Astronomers reveal contents of mysterious black hole jets

An international team of astronomers has answered a long standing question about the enigmatic jets emitted by black holes.

The team studied the radio waves and X-rays emitted by a small black hole a few times the mass of the Sun. The black hole in question was known to be active, but the team’s radio observations did not show any jets, and the X-ray spectrum didn’t reveal anything unusual.

However, a few weeks later, the team took another look and this time saw radio emissions corresponding to the sudden appearance of these jets, and even more interestingly, lines had appeared in the X-ray spectrum – the tell-tale signature of ordinary atoms – around the black hole.

Read More.