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Wireless communication breaks through water-air barrier

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MIT researchers have taken a step toward solving a longstanding challenge with wireless communication: direct data transmission between underwater and airborne devices.

Today, underwater sensors cannot share data with those on land, as both use different wireless signals that only work in their respective mediums. Radio signals that travel through air die very rapidly in water. Acoustic signals, or sonar, sent by underwater devices mostly reflect off the surface without ever breaking through. This causes inefficiencies and other issues for a variety of applications, such as ocean exploration and submarine-to-plane communication.

In a paper being presented at this week’s SIGCOMM conference, MIT Media Lab researchers have designed a system that tackles this problem in a novel way. An underwater transmitter directs a sonar signal to the water’s surface, causing tiny vibrations that correspond to the 1s and 0s transmitted. Above the surface, a highly sensitive receiver reads these minute disturbances and decodes the sonar signal.

“Trying to cross the air-water boundary with wireless signals has been an obstacle. Our idea is to transform the obstacle itself into a medium through which to communicate,” says Fadel Adib, an assistant professor in the Media Lab, who is leading this research. He co-authored the paper with his graduate student Francesco Tonolini.

The system, called “translational acoustic-RF communication” (TARF), is still in its early stages, Adib says. But it represents a “milestone,” he says, that could open new capabilities in water-air communications. Using the system, military submarines, for instance, wouldn’t need to surface to communicate with airplanes, compromising their location. And underwater drones that monitor marine life wouldn’t need to constantly resurface from deep dives to send data to researchers.

Another promising application is aiding searches for planes that go missing underwater. “Acoustic transmitting beacons can be implemented in, say, a plane’s black box,” Adib says. “If it transmits a signal every once in a while, you’d be able to use the system to pick up that signal.”

Decoding vibrations

Today’s technological workarounds to this wireless communication issue suffer from various drawbacks. Buoys, for instance, have been designed to pick up sonar waves, process the data, and shoot radio signals to airborne receivers. But these can drift away and get lost. Many are also required to cover large areas, making them impracticable for, say, submarine-to-surface communications.

TARF includes an underwater acoustic transmitter that sends sonar signals using a standard acoustic speaker. The signals travel as pressure waves of different frequencies corresponding to different data bits. For example, when the transmitter wants to send a 0, it can transmit a wave traveling at 100 hertz; for a 1, it can transmit a 200-hertz wave. When the signal hits the surface, it causes tiny ripples in the water, only a few micrometers in height, corresponding to those frequencies.

To achieve high data rates, the system transmits multiple frequencies at the same time, building on a modulation scheme used in wireless communication, called orthogonal frequency-division multiplexing. This lets the researchers transmit hundreds of bits at once.

Positioned in the air above the transmitter is a new type of extremely-high-frequency radar that processes signals in the millimeter wave spectrum of wireless transmission, between 30 and 300 gigahertz. (That’s the band where the upcoming high-frequency 5G wireless network will operate.)

The radar, which looks like a pair of cones, transmits a radio signal that reflects off the vibrating surface and rebounds back to the radar. Due to the way the signal collides with the surface vibrations, the signal returns with a slightly modulated angle that corresponds exactly to the data bit sent by the sonar signal. A vibration on the water surface representing a 0 bit, for instance, will cause the reflected signal’s angle to vibrate at 100 hertz.

“The radar reflection is going to vary a little bit whenever you have any form of displacement like on the surface of the water,” Adib says. “By picking up these tiny angle changes, we can pick up these variations that correspond to the sonar signal.”

Listening to “the whisper”

A key challenge was helping the radar detect the water surface. To do so, the researchers employed a technology that detects reflections in an environment and organizes them by distance and power. As water has the most powerful reflection in the new system’s environment, the radar knows the distance to the surface. Once that’s established, it zooms in on the vibrations at that distance, ignoring all other nearby disturbances.

The next major challenge was capturing micrometer waves surrounded by much larger, natural waves. The smallest ocean ripples on calm days, called capillary waves, are only about 2 centimeters tall, but that’s 100,000 times larger than the vibrations. Rougher seas can create waves 1 million times larger. “This interferes with the tiny acoustic vibrations at the water surface,” Adib says. “It’s as if someone’s screaming and you’re trying to hear someone whispering at the same time.”

To solve this, the researchers developed sophisticated signal-processing algorithms. Natural waves occur at about 1 or 2 hertz — or, a wave or two moving over the signal area every second. The sonar vibrations of 100 to 200 hertz, however, are a hundred times faster. Because of this frequency differential, the algorithm zeroes in on the fast-moving waves while ignoring the slower ones.

Testing the waters

The researchers took TARF through 500 test runs in a water tank and in two different swimming pools on MIT’s campus.

In the tank, the radar was placed at ranges from 20 centimeters to 40 centimeters above the surface, and the sonar transmitter was placed from 5 centimeters to 70 centimeters below the surface. In the pools, the radar was positioned about 30 centimeters above surface, while the transmitter was immersed about 3.5 meters below. In these experiments, the researchers also had swimmers creating waves that rose to about 16 centimeters.

In both settings, TARF was able to accurately decode various data — such as the sentence, “Hello! from underwater” — at hundreds of bits per second, similar to standard data rates for underwater communications. “Even while there were swimmers swimming around and causing disturbances and water currents, we were able to decode these signals quickly and accurately,” Adib says.

In waves higher than 16 centimeters, however, the system isn’t able to decode signals. The next steps are, among other things, refining the system to work in rougher waters. “It can deal with calm days and deal with certain water disturbances. But [to make it practical] we need this to work on all days and all weathers,” Adib says.

“TARF is the first system that demonstrates that it is feasible to receive underwater acoustic transmissions from the air using radar,” says Aaron Schulman, an assistant professor of computer science and engineering at the University of California at San Diego. “I expect this new radar-acoustic technology will benefit researchers in fields that depend on underwater acoustics (for example, marine biology), and will inspire the scientific community to investigate how to make radar-acoustic links practical and robust.”

The researchers also hope that their system could eventually enable an airborne drone or plane flying across a water’s surface to constantly pick up and decode the sonar signals as it zooms by.

The research was supported, in part, by the National Science Foundation.

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Press mentions, smithsonian magazine.

Smithsonian reporter Emily Matchar highlights how MIT researchers have developed a new system that enables data sharing between underwater and airborne devices. Prof. Fadel Adib explains that the technology could be used to “study marine life and have access to a whole new world that is still pretty much out of our reach today.”

IEEE Spectrum

Prof. Fadel Abid speaks with IEEE Spectrum reporter Michael Koziol about a new system his research group developed to enable communication between underwater sources and the air. “We’re very interested in how deep and how high you can go,” says Adib. “Even from a theoretical perspective, we don’t even know what the limits are.”

FOX News reporter Jamie Rogers writes that MIT researchers have developed a new system that “helps solve a longstanding problem in wireless communication – how to send data directly from a submarine to a plane or drone.”

MIT researchers have developed a new system that allows data to be transmitted between underwater and airborne devices, according to the BBC News. The system could enable submarines to communicate with planes, and in the future the device could “help planes or drones detect the location of a submerged ‘black box’ flight recorder.”

Engadget reporter Jon Fingas writes that MIT researchers have developed a new wireless device that allows data to be transmitted from an underwater source to the air. Fingas explains that the system could allow submarines to “send their findings directly to aircraft (including drones) circling above while remaining safely underwater, and without using boats as intermediaries.”

Popular Mechanics

Popular Mechanics reporter Avery Thompson describes a new method developed by MIT researchers to send signals between the water and the air by using sound waves to create detectable vibrations at the water’s surface. Thompson explains that the new technology could eventually make “exploring and living under the waves much easier.”

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by Chris Woodford . Last updated: January 28, 2024.

Photo: A truck-mounted satellite dish antenna. Photo by courtesy of NASA Glenn Research Center and Internet Archive .

Artwork: How a transmitter sends radio waves to a receiver. 1) Electricity flowing into the transmitter antenna makes electrons vibrate up and down it, producing radio waves. 2) The radio waves travel through the air at the speed of light. 3) When the waves arrive at the receiver antenna, they make electrons vibrate inside it. This produces an electric current that recreates the original signal.

Photo: A parabolic reflector dish (1) catches incoming waves and bounces them up to a much smaller, concentrating "subreflector" above and in the center of the dish (2), from which they're reflected down for processing (3). A dish like this can also work as a transmitter, simply by sending radio beams in the opposite direction. Deep Space Network antenna photo courtesy of NASA .

Artwork: How a wave travels from a transmitter to a receiver: 1) By line of sight; 2) By ground wave; 3) Via the ionosphere.

Photo: Antennas that use line-of-sight communication need to be mounted on high towers, like this. You can see the thin dipoles of the antenna sticking out of the top, but most of what you see here is just the tower that holds the antenna high in the air. Photo by Pierre-Etienne Courtejoie courtesy of US Army.

Photo: The AM "loopstick" antenna inside a typical transistor radio is very compact and highly directional. The pink-colored wire that makes up the antenna is wrapped around a thick ferrite core (the black rod). Usually, as you can see here, there are two separate antennas on the same ferrite rod: one for AM (medium-wave) and one for LW (long-wave).

Artwork: Top: Electromagnetic radio waves consist of vibrating electric waves (blue) and magnetic waves (red) traveling together at the speed of light (black arrow). Bottom: Left: An FM antenna picks up the relatively short wavelength, high-frequency electric part of FM radio waves. Right: An AM ferrite loop antenna picks up and concentrates the magnetic parts of longer wavelength, lower frequency electromagnetic waves.

Photo: 1) This telescopic FM radio antenna pulls out to a length of about 1–2m (3–6ft or so), which is roughly half the length of the radio waves it's trying to capture. 2) Cellphones have particularly compact antennas. Older ones (like the Motorola on the left) have stubby external antennas or ones that pull out telescopically. (The exposed part of the antenna is the bit my finger is pointing to and there's another part we can't see running around the edge of the circuit board inside the case.) Newer cellphones (like the Nokia model on the right) have longer antennas built completely inside the case.

Photos: A "bowtie antenna" (held by the man on the left) is a variation on a basic dipole. The diagonally angled wires help it to pick up a wider range of frequencies, which is why small bowties were often used indoors with basic TV sets (to pick up a good selection of channels). Photo by Andrew Ochoa courtesy of US Marine Corps and DVIDS .

Artwork: Four common types of antenna (red) and the places where they pick up best (orange): A basic dipole, a folded dipole, a dipole and reflector, and a Yagi. A basic or folded dipole antenna picks up equally well in front of or behind its poles, but poorly at each end. An antenna with a reflector picks up much better on one side than the other, because the reflecting element (the red, dipole-like bar on the left) bounces more signal over to the folded dipole on the right. The Yagi exaggerates this effect even more, picking up a very strong signal on one side and almost no signal anywhere else. It consists of multiple dipoles, reflectors, and directors.

Directionality

Photo: Directionality: Dipole antennas like this are highly directional. Here, the antenna is being used to track tortoises in the desert for a conservation project. Photo by Dave Flores courtesy of US Marine Corps and DVIDS .

Photo: Gain: The Apollo 17 mission's lunar rover (pictured here on the Moon in December 1972) carried a high-gain, foldable parabolic-reflector antenna (top right) that resembled an umbrella. Photo courtesy of NASA .

Photos: Bandwidth. Mobile devices typically use compact microstrip antennas (printed directly onto circuit boards) designed to work at very limited, specific frequencies, so they tend to have a narrow bandwidth. 1) The antenna that powers an RFID tag stuck inside a library book. The circuit inside it has no power source: it gets all its energy from the incoming radio waves, typically 13.56MHz (per the International Standard ISO 18000). 2) The dipole antenna inside a PCMCIA wireless Internet Wi-Fi card. This one works with 2.4GHz radio waves of wavelength 12.5cm, which is why it only needs to be about 6cm long or so in total.

Photo: The largely forgotten radio pioneer Sir Oliver Lodge (1851–1940). Photo courtesy of Bain News Service and US Library of Congress .

Artwork: Oliver Lodge's illustration of sending radio waves through space from a transmitter (red) to a receiver (blue) some distance away, taken from his 1898 patent US 609,154: Electric Telegraphy . Courtesy of US Patent and Trademark Office.

If you liked this article...

Find out more, on this website.

• Cellphones (Mobile phones)
• History of communication
• Radio frequency (RF and RFID) tags
• Antenna Engineering Handbook by John L. Volakis (ed). McGraw-Hill, 2018. A huge, definitive, theoretical and practical guide to all the common types of antenna.
• Antenna Theory: Analysis and Design by Constantine A. Balanis. Wiley, 2016. A good, general, theoretical introduction aimed at physics and electrical engineering undergraduates. Not really suitable for beginners—and you will need a decent grasp of math.
• Small Antennas: Miniaturization Techniques & Applications by John L. Volakis et al. McGraw-Hill, 2010. A look at the theory and practical design of small antennas for cellphones, RFID, and other applications.
• Antenna Theory and Practice by Rajeswari Chatterjee. New Age International, 2006.
• No Antenna Could Survive Europa's Brutal, Radioactive Environment—Until Now by Nacer E. Chahat, IEEE Spectrum, 21 Jul 2021. How do you design antennas for the extremes of space?
• Tiny Membrane-Based Antennas by Charles Q. Choi. IEEE Spectrum, 22 Aug 2017. Cutting-edge antennas can now be shrunk to 1/000 the length of the wavelength they need to pick up.
• Tunable Liquid Metal Antennas for Tuning in to Anything by Alexander Hellemans. IEEE Spectrum, 19 May 2015. What kind of antennas will we need for higher-frequency, shorter-wavelength radio applications in the future?
• Apple Patent Cleverly Hides Antenna in Your Keyboard by Christina Bonnington. Wired, 17 August 2011. How Apple keyboards hide wireless antennas under the keys.
• Inside Apple's Antenna Design Lab by Brian X. Chen. Wired, 16 July 2010. A tour of Apple's secret antenna-testing laboratory.
• Rabbit Ears Perk Up for Free HDTV by Matt Richtel and Jenna Wortham. The New York Times, December 5, 2010. Viewers tired of cable prices are rediscovering the joys of old-fashioned antennas and free TV.
• Signal boost for mobile phones : BBC News, 22 April 2008. How Oxford scientists have developed a more sophisticated cellphone antenna.
• As Cars Become More Connected, Hiding the Antennas Gets Tougher by Ivan Berger. The New York Times, March 14, 2005..
• Hacking with a Pringles tube by Mark Ward, BBC News, 8 March 2002. An interesting news story explaining how hackers have used directional antennas made from Pringles tubes to break into wireless networks.
• What you should know about TV antennas by Robert Hertzberg, Popular Science, December 1950. This old article from the Popular Science archives remains a very clear and relevant introduction to antenna design.

Text copyright © Chris Woodford 2008, 2018. All rights reserved. Full copyright notice and terms of use .

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Unit 13: How radios and cellphones catch signals from air?

The electronic components inside every radio and cellphone.

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What radio waves can travel through and what they cannot.

When Guglielmo Marconi began research into long-range radio in the late 19th century, the scientific community was skeptical. That he succeeded in transmitting radio signals more than 2000km met with much astonishment. What he had unwittingly done was discover the ionosphere, a layer in the atmosphere that is ionized to a degree by the sun’s ultraviolet rays. 

This affects radio waves and reflects them to earth, which bounces them upwards again. This repeated sequence enables us to transmit radio waves around the world. So, if radio waves can’t penetrate the ionosphere, what else will hinder them? Let’s look at what radio waves consist of, and then we’ll talk about their ability or otherwise to pass through certain materials.

Radio Waves Explained 

Developments in radio technology have brought us a long way in the past 100 years and more, but how do radio waves work? Before Marconi’s discovery, scientists believed that radio signals could only travel a straight line, as they were known to do in free space. Hence, there was a necessity for tall towers from which to transmit signals. A 100m high tower, for example, could send a signal up to around 30km, the limit set by the curvature of the earth. Marconi showed that radio waves could be bent and bounced by the ionosphere.

Radio waves form a small part of what is known as the electromagnetic spectrum (EMS). This consists not just of radio waves but also other forms of electromagnetic radiation such as gamma rays, microwaves, visible light, and more. Radio waves have among the longest wavelengths on the EMS. Imagine a rope held between two people. Move the rope up and down at one end, and a waveform moves across the rope.

This is what a radio wave would look like if we could see it. The wavelength is the distance between two ‘peaks’ in the wave. We also have to consider the frequency, which the number of waves that pass a given point in a set time. This is vital to understand so that different transmissions do not interfere with each other. 

Television signals are radio waves, but they are broadcast in a different frequency range to the radio.

What has this to do with the materials that radio waves can and cannot pass through? Let’s look more closely at this. 

What Can’t Radio Waves Pass-Through?

We’ve already seen that radio waves do not penetrate the ionosphere. We should explain that this refers to radio waves of up to 40MHz, the highest frequency bounced off the ionosphere. Why do radio waves bounce back?

As we mentioned, the ionosphere is partly ionized. 

This is because the UV light from the sun causes electrons to shake free from atoms, leaving a large proportion of free electrons hanging about in the ionosphere. When a radio wave hits the ionosphere, the energy created by the free electrons, as a result, causes the radio waves to be repelled or reflected. 

So, we know that radio waves up to 40MHz won’t pass through an ionized layer in the atmosphere. Remember that we explained the perceived limitations of radio transmissions before Marconi’s discovery. A line of sight was necessary, without obstructions, for successful transmission.

In some radio transmissions, interference can be caused by the waves being blocked by materials that they cannot penetrate. While radio waves can move through wood, bricks, and concrete to a certain extent, these materials can still cause interference. This is because radio waves meeting such objects can be reflected from buildings and other large structures, just like the ionosphere. This explains why the reception of radios and other radio frequency devices such as smartphones vary between locations.

For the record, as it covers a large bandwidth necessarily, television signals need to be above 40MHz so they cannot be bounced off the ionosphere, hence the tall towers in high locations used for TV transmissions. 

Radio waves will also be adversely affected by metal and water, which they cannot pass through. That is because water and metal are both electrical conductors. Like the ionosphere, metal and water contain many free electrons, which will vibrate when a radio wave hits the surface, and the wave will bounce back. 

To summarize, we now know that radio waves are affected by free electrons in electrical conductors such as metals and water and cannot pass through these materials. 

We have discovered that they can pass through non-conducting materials quite well but are losing propagation power with reflecting surfaces such as water, metal, and other materials. Furthermore, worldwide radio transmission is made possible by the radio waves being reflected by the ionosphere and the earth in a continuous sequence, allowing for transmissions to be made across great distances. 

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Exploring How WiFi Signal Travel Works: An In-Depth Look at the Physics, Antennas, Interference, Frequency Bands, and Directional Signals

By Happy Sharer

Exploring the Basics of WiFi Signal Travel

Wireless networks have become a vital part of our lives. We use them to connect devices to the internet, share files, and even control home appliances. But have you ever wondered how these WiFi signals travel? In this article, we explore the basics of WiFi signal travel and take an in-depth look at the physics behind it, the role of antennas, interference, frequency bands, and directional signals.

What is a WiFi Signal?

A WiFi signal is a type of wireless network that uses radio waves to transmit data between two or more devices. It is based on the IEEE 802.11 standard, which defines the rules for how wireless networks should operate. This standard defines multiple frequency bands, including 2.4 GHz and 5 GHz, which are used by most wireless networks today.

How Does a WiFi Signal Travel?

WiFi signals travel through the air using electromagnetic waves. These waves are transmitted from a device’s antenna and spread out in all directions. The further away the receiving device is from the transmitting device, the weaker the signal will be. This means that the signal strength will decrease over distance, so it is important to have strong antennas that can broadcast the signal far enough for it to reach its destination.

Understanding the Physics Behind WiFi Signal Propagation

In order to understand how WiFi signals travel, it is important to first understand the principles of wave propagation. According to the laws of physics, waves spread out in all directions from their source, and the power of the wave decreases as it moves further away. This is known as the inverse-square law. This means that the signal strength at any given point is inversely proportional to the square of the distance from the source of the signal.

For example, if the signal strength at one point is 1 watt, then at a distance of 2 meters the signal strength will be 0.25 watts. At a distance of 4 meters, the signal strength will be 0.0625 watts, and so on. This is why it is important to have strong antennas that can broadcast the signal far enough to reach its destination.

The Role of Interference in WiFi Signal Strength

Interference is another factor that affects the strength of a WiFi signal. Interference can come from other wireless networks, microwaves, Bluetooth devices, cordless phones, and other sources. This interference can cause the signal to be weaker than it would otherwise be, reducing the signal range and making it difficult for devices to communicate with each other.

Examining the Role of Antennas in WiFi Signal Distribution

Antennas are used to broadcast and receive WiFi signals. Different types of antennas are used for different applications, such as omnidirectional antennas that broadcast a signal in all directions, or directional antennas that focus the signal in a particular direction. The type of antenna used and the placement of the antenna can have a major impact on the signal quality.

For example, an omnidirectional antenna will provide a stronger signal in all directions, while a directional antenna will provide a stronger signal in the direction it is pointed. The placement of the antenna can also affect the signal strength, as placing the antenna too close to a wall or other object can reduce the signal strength.

Investigating the Impact of Interference on WiFi Signal Strength

Interference can have a major impact on the strength of a WiFi signal. There are several types of interference that can disrupt WiFi signals, including radio frequency interference, physical obstructions, and multipath fading. Radio frequency interference comes from other wireless networks or other electronic devices, and can reduce the signal strength significantly.

Physical obstructions, such as walls, can also reduce the signal strength, as they block the signal from reaching its destination. Multipath fading occurs when the signal bounces off of objects and arrives at the receiving device at different times, causing the signal to become distorted and weak.

There are several strategies that can be used to minimize interference, such as choosing the right frequency band, using directional antennas, and avoiding physical obstructions. Additionally, using a higher gain antenna can help increase the signal strength, as it can broadcast the signal further.

Exploring How Different Frequency Bands Affect WiFi Signal Quality

WiFi signals use different frequency bands, such as 2.4 GHz and 5 GHz. Each frequency band has its own advantages and disadvantages. For example, the 2.4 GHz band has a longer range but is more susceptible to interference, while the 5 GHz band has a shorter range but is less susceptible to interference.

Additionally, the 2.4 GHz band is better at penetrating walls and other obstacles, while the 5 GHz band is better at handling more data at once. It is important to choose the right frequency band for your specific needs, as this can have a major impact on the signal quality.

Examining the Benefits of Directional WiFi Signals

Directional WiFi signals can be used to improve the signal quality and reduce interference. Directional antennas focus the signal in one direction, which helps reduce interference and increases the signal strength. Additionally, directional antennas can be used to create “hotspots” in specific areas, such as a conference room or auditorium.

Setting up a directional WiFi signal requires careful placement of the antennas and careful consideration of the surrounding environment. Additionally, the antennas must be properly configured to ensure that the signal is focused in the desired direction.

In conclusion, WiFi signals travel through the air using electromagnetic waves. Understanding the physics behind this process, as well as the role of antennas, interference, frequency bands, and directional signals, can help us optimize our wireless networks and improve signal quality. By following the tips outlined in this article, we can maximize the performance of our wireless networks and enjoy a reliable connection.

(Note: Is this article not meeting your expectations? Do you have knowledge or insights to share? Unlock new opportunities and expand your reach by joining our authors team. Click Registration to join us and share your expertise with our readers.)

Hi, I'm Happy Sharer and I love sharing interesting and useful knowledge with others. I have a passion for learning and enjoy explaining complex concepts in a simple way.

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La presentación del X-59 de la NASA personifica la tradición aeronáutica

Spectrum overview.

Jermaine Walker

What is the spectrum made of, how is the spectrum used , what is electromagnetic energy, characteristics, analog vs. digital.

Virtually every endeavor that NASA undertakes requires communications or data transfer via the electromagnetic spectrum. NASA relies solely on Space Communications and Navigation (SCaN) to provide this vital service to all of its missions. Today and in the coming years, NASA will implement programs encompassing space exploration, scientific research, technology development, and all of these efforts will need access to this limited resource.

The  electromagnetic spectrum is comprised of all frequencies  of electromagnetic radiation that propagate energy and travel through space in the form of waves. Longer wavelengths with lower frequencies make up the  radio spectrum . Shorter wavelengths with higher frequencies make up the  optical spectrum.  The portion of the spectrum that humans can see is called the visible spectrum. However, NASA utilizes a number of tools that allow us to communicate and create images utilizing almost every single component of the electromagnetic spectrum in one way or another.

People use the electromagnetic spectrum every day. The car radio, television, smart phone and microwave are just a few examples of the electromagnetic spectrum used every day.

Frequency  and  wavelength  are both forms of electromagnetic energy. Frequency refers to the number of crests that pass a give point. One wave, or cycle, per second, is called a Hertz (Hz). Wavelength refers to the distance between crests and they range in size from very small to very big as seen in the illustration below. Electromagnetic energy travels in waves and spans a broad spectrum from very long radio waves to very short gamma rays. Electromagnetic waves do not need a medium in order to propagate, which means they can travel through air, solid materials, and also through the vacuum of space. 

The characteristics of the electromagnetic spectrum are the propagation features and the amount of information, which signals can carry. In general, signals sent using the higher frequencies have shorter propagation distances but a higher data-carrying capacity. These physical characteristics of the spectrum limit the range of applications for which any particular band is suitable. Some spectrum (such as in the (UHF) band 300-3000 MHz) is known to be suitable for a wide variety of services and is in great demand.

There are two important types of transmissions to understand:  analog and digital . Analog signal transmission information (sound, video, or data) travels in a continuous wave whose strength and frequency vary directly with a changing physical quantity at the source. Digital signal transmission information is converted to ones and zeros which are formatted and sent as electrical pulses. Advantages of using digital signals include greater accuracy, noise reduction (unwanted signals) and an increased capacity for sending information.

Electromagnetic spectrum is a limited natural resource. The spectrum waves naturally propagate outward in all directions. Transmitters can be focused to transmit their signals to a single specified location. Likewise, receivers can be focused to maximize signal reception. The receiving antenna may still detect unintended signals that can interfere with the reception of the intended signal. To avoid signal interference problems, multiple users cannot transmit radio signals at the same frequencies, at the same time in the same direction. As soon as one user stops transmitting signals over a portion of the spectrum, another can immediately re-use it. The spectrum is scarce; at any given time and place, one use of a frequency precludes its use for any other purpose.

How Fast Do Radio Waves Travel In A Vacuum-Air-Space

Last Updated: February 1, 2024

The effective use of radio waves in communication technologies today is based on how fast radio waves travel.

Radio waves play a significant role in most of the technology solutions we see around us.

But, as common as they are, very little is known about them. For most people, they don’t even know the meaning of radio waves.

There is a lot of misconception out there regarding radio waves. From what they are to how they function, only a handful of people know anything about this wave type.

As a result, this post will be breaking down everything you need to know about radio waves.

By the time you are done reading this, you should be confident enough to tell someone else exactly what radio waves are and how they function.

What are radio waves?

Unlike what many people think, radio waves are not the sounds you hear coming out of your radio speakers. That is sound waves, not radio waves.

Radio waves are electromagnetic radiation. Radio waves are quite similar to light waves. The only difference is that you cannot see them as light.

Think of them as being produced by charged particles going through acceleration, like in time-changing electric currents.

Transmitters artificially generate them. You need a radio receiver to intercept and receive the radio waves with the help of an antenna.

The application of radio waves is used in many technologies.

They are employed in mobile and fixed radio communication, radar & navigation systems, broadcasting, wireless computer network, communication satellites, and a host of others.

Radio waves were discovered by James Clerk Maxwell, the physicist who was known for the famous Maxwell’s Equation around the 1870s.

A German physicist known as Heinrich Hertz was the one who advanced Maxwell’s prediction of radio waves.

He was the first to apply Maxwell’s equation to the transmission and reception of radio waves.

The unit of frequency for EM waves was unanimously agreed to be Hertz by the American Association For The Advancement of Science, in honor of Heinrich Hertz.

Properties of radio waves

Radio waves have got some highly distinct properties that you ought to be aware of. Those properties will be outlined below

• They are a form of electromagnetic waves. They have got a wavelength longer than the wavelength of infrared light.
• Radio waves can go through materials or obstacles.
• They can travel extremely long distances.
• Radio waves are invisible and cannot be felt either.
• When they move through a vacuum, they do so at the speed of light. But, their speed drops when they move through a medium, depending on the medium’s permeability.
• Radio waves have a wavelength range between thousands of meters and 30cm.
• Radio waves can be formed as a result of changing electric currents. Naturally, they can be emitted by lightning and astronomical objects that can exhibit magnetic field changes.
• Radio waves possess both magnetic and electric components
• They can experience absorption, refraction, reflection, as well as polarization.

Types of Radio Wave

Radio waves are subdivided into various categories. This section of this post will be discussing the different radio waves, as seen below.

Low to medium frequencies

This frequency range is the first category in the radio frequency spectrum. It is composed of extremely low to medium radio waves.

ELF and VLF stand for extremely low frequency and very low frequency, respectively. This class of radio waves operates with a frequency of between 0.1 and 30 kHz.

They are classified as the lowest radio frequencies. They’ve got long-range capabilities that make them suitable for communication items in submarines.

That is because they can penetrate water and rocks. They have also found useful applications in caves and mines.

Higher frequencies

HF, VHF, and UHF bands comprise public service radio, broadcast television sound, cellphones, FM, and GPS.

These bands employ FM or frequency modulation to impress or encode a data or audio signal upon the carrier wave.

In FM, the signal’s amplitude is kept constant, while the frequency is varied along with the magnitude and rate that corresponds to the data or audio signal.

That is why the signal quality of FM is better than that of AM. Environmental factors do not have a similar influence on frequency as they do on amplitude.

Furthermore, the FM receivers are built to ignore any amplitude variations so long as the signal maintains the least threshold value.

Shortwave radio

Shortwave radio makes use of frequencies between 1.7 kHz and 30 MHz.

This frequency range is what is used to transmit radio signals from shortwave stations across the globe.

Stations like the BBC, VOA, Voice of Russia, and hundreds of other stations use this frequency range for broadcast purposes.

Shortwaves are preferred for long-distance broadcast due to their signals’ ability to reflect on the ionosphere and rebound back far away from where the signal has been broadcast.

Highest frequencies

Super high frequency (SHF) and extremely high frequency (EHF) are considered among the microwave band of the radio-frequency spectrum.

With the help of this frequency range, high-bandwidth, short-range communications can happen between fixed locations.

SHF is used in applications such as Wi-Fi, wireless USB, and Bluetooth. They are also employed for radar purposes because they possess the ability to bounce off obstacles.

It is noteworthy that SHF can only function in straight paths. They bounce off any obstacle they come in contact with.

How Fast Do Radio Waves Travel? Through Space, Air or Vacuum

How fast do radio waves travel has been answered so many times, yet some people are still confused about the subject.

Earlier, we were able to establish that radio waves are electromagnetic. That means they are going to behave like electromagnetic waves too.

One thing that is common to all electromagnetic waves is that they all travel at the speed of light in a vacuum. They travel at an approximate speed of 186,000 miles per second in a vacuum.

Unlike radio waves, sound waves cannot travel through a vacuum. They can only travel through a medium.

In other words, without a medium, you cannot have sound. Radio waves do not necessarily need any medium for their propagation.

Radio waves travel at the same speed as light because they are like light waves, except that they are unseen.

Radio waves can equally travel through various mediums at different speeds. How fast they are going to travel through a specific medium will be determined by some factors.

Some of those factors include the permittivity and permeability of the medium in question.

Radio waves are much faster than sound waves, even if you have to pass them through the same medium for the sake of comparison.

How do radio waves work?

The best way to answer how do radio waves work is by using antennas to explain the concept.

For radio waves to be effectively broadcast and received, we will need two antennas. One will be the transmitter, while the other will be the receiver.

Let’s use a radio station as an example. At the radio station, voice can be captured by a mic, where the system will convert it into a form of electrical energy.

That electricity is then sent through an antenna (transmitter) with great height. The transmitter will boost the power of the electricity so it can travel as far as possible.

The tiny particles within the electric current continuously move back and forth within the antenna, and radio waves are automatically produced.

The radio waves then travel at the speed of light or close to that value, with the voices trapped within them.

Therefore, when someone puts on their radio set, the electrons in their antenna are made to move back and forth (vibrated) by the incoming radio waves.

That resonating action brings about an electric current. The electronics component then converts that electric signal to sound, allowing you to hear the voice recorded at the station.

Why do radio waves travel at the speed of light and not sound?

Sound waves need a medium before they can travel between locations.

For example, let’s take the air; sound waves can travel through the air because it is composed of molecules.

Without any molecules in the air, it will be impossible to transmit sound waves across the atmosphere. That is where radio waves differ from sound waves.

Radio waves travel at the speed of light because both light and radio waves belong to electromagnetic waves.

Sound waves do not belong to this class. Instead, they are grouped in the class of mechanical waves.

All electromagnetic waves can travel through a vacuum at the speed of light. So that is the simple reason radio waves tend to travel at the speed of light and not sound waves.

FAQs Regarding The Speed of Radio Waves

Do all the different types of radio waves travel at the same speed.

The radio frequency spectrum is a composition of the different types of radio waves.

But because the radio waves are a part of an electromagnetic spectrum, they will all travel at the same speed across a vacuum.

That speed is the speed of light. Having said that, if they are to travel across different mediums, then their speeds will vary.

Do radio waves continue in outer space?

Yes, radio waves continue indefinitely until they come in contact with something.

But, even before that happens, they usually become weak and blend with the universe’s background noise.

That means the first set of radio waves emitted into outer space must be over a hundred light-years old by now.

What is the speed of red light in a vacuum?

Light travels through a vacuum at a constant speed. The speed at which light travels through a vacuum has nothing to do with its polarization, frequency, or other light wave characteristics.

In other words, the color of the wave does not affect its speed in a vacuum. Whether it is blue or red light, it will travel at an approximate speed of 300,000 km per second.

Does Wi-Fi make use of radio waves?

Just like other wireless devices, Wi-Fi implements radio frequencies for sending signals between devices.

The range of radio frequencies employed by Wi-Fi is quite different from devices like cell phones, car radios, weather radios, or walky-talkies.

For instance, your car radio receives frequencies in the range of between Kilohertz and Megahertz, suitable for AM and FM stations, respectively.

Wi-Fi, on the other hand, implements its data transmission in the region of Gigahertz. So, in general, you can say that Wi-Fi uses radio waves for transmitting data between devices.

What are some of the uses of radio waves?

Radio waves possess the longest wavelengths in the EM spectrum. Radio waves aren’t just used for transmitting radio signals that your radio can pick up.

They are actively responsible for carrying the signals you use for your cell phones and TV.

The moment your TV antenna picks up an incoming signal from a TV station, it does that in the form of radio waves or EM waves.

Are radio waves the only type of electromagnetic wave?

The answer to this question is No! Radio waves are not the only component of the electromagnetic spectrum.

Other forms of electromagnetic waves include Bluetooth, radar, microwaves, ultraviolet light waves, infra-red, and X-rays.

So it is right for you to assume all these components as electromagnetic waves.

Waves are generally classified into two groups – mechanical waves and electromagnetic waves.

Radio waves belong to the group of the latter. That explains the reason behind their ability to travel through a vacuum.

In stark contrast, sound waves are unable to travel through a vacuum due to their mechanical properties.

Sound waves require a medium for them to be propagated from one point to another.

Radio waves, just like other electromagnetic waves, travel through a vacuum at the speed of light.

Radio waves are employed in a wide range of technology applications. They make up the very core of communication technology.

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Tuning Into the Atmosphere: How Humidity Influences AM Radio Signal Propagation

One of the oldest forms of electronic communication, AM (Amplitude Modulation) radio, still holds an essential place in modern life. Be it for weather forecasts, news, sports commentary, or simply listening to music, AM radio serves us in numerous ways. However, the quality and distance these AM signals can travel are significantly affected by various atmospheric conditions, particularly humidity. This article explores the relationship between humidity and AM radio signal propagation.

The Journey of AM Radio Waves

AM radio signals operate in the Medium Frequency (MF) band of the electromagnetic spectrum, usually from 535 kHz to 1605 kHz. These signals, due to their long wavelength, can diffract around obstacles like buildings or hilly terrains and follow the Earth’s curvature, making them suitable for long-distance broadcasting.

One intriguing characteristic of AM radio signals is their ability to bounce off the Earth’s ionosphere, particularly during the night. The ionosphere is a layer of the atmosphere filled with free electrons and ions. At night, as the lower ionospheric layers recede due to reduced solar radiation, the higher layers reflect the MF band signals back to Earth, enabling the signals to cover vast distances. This phenomenon, known as “skywave” propagation, can sometimes allow AM radio signals to travel thousands of kilometers.

Humidity and AM Radio Signals

Humidity, defined as the amount of water vapor in the air, influences AM radio signals significantly. The primary impact comes from the fact that water molecules can absorb electromagnetic radiation, including the frequencies used by AM radio.

In high humidity conditions, there are more water molecules present in the air, which can lead to increased absorption of AM radio signals. This absorption results in signal loss and reduced signal strength, potentially affecting the quality of the broadcast received.

Moreover, the density of the air changes with the level of humidity. Humid air is less dense than dry air because water molecules are lighter than nitrogen and oxygen molecules, which make up most of our atmosphere. Changes in air density can cause radio signals to refract, or bend, which can affect the direction and distance they travel.

Implications for Radio Signal Distance

Understanding the impacts of humidity on AM radio signals is crucial in predicting and maximizing their reach. Generally, higher humidity levels can reduce the distance AM radio signals can effectively travel, especially during periods of extremely high humidity or heavy rainfall. These conditions can lead to greater signal loss due to increased absorption and refraction by water molecules.

However, it’s important to note that other atmospheric conditions, such as temperature and pressure, also play a significant role in radio wave propagation. For instance, temperature inversions—when the temperature increases with height instead of decreasing—can cause radio signals to bend back towards the Earth and travel longer distances. Such factors can sometimes counterbalance the effects of high humidity.

Humidity’s impact on AM radio signal propagation underscores the intricate relationship between our planet’s atmospheric conditions and our technological systems. By understanding these effects, radio engineers and broadcasters can better predict signal coverage and troubleshoot reception issues, ensuring that the airwaves continue to serve as a reliable means of information and entertainment.

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Can you hear me now: How pilots communicate with ATC while 35,000 feet in the air

When you're in a sealed, pressurized tube five miles above the ground, being able to communicate effectively is essential. In the early days of aviation , flags and light signals were used before designers were able to fit basic radio equipment into aircraft.

Modern aircraft now have an array of communication devices from the rudimentary HF radios of old to sophisticated satellite-based systems that enable us to talk almost as if we were on a mobile phone.

How it works

The most common form of communication in aviation, very high frequency (VHF) radio calls are what we use for around 95% of our communications with ATC . In simplified terms, the transmitting station sends a signal that travels in a straight line and is picked up by the receiving station.

VHF comms provide clear voice communications. However, as the radio signals travel in straight lines, they are limited by the curvature of the earth and objects that they may come into contact with, such as hills and mountains.

The distance which a VHF signal can travel depends on both the height from which the signal is sent and the height of the receiving station. If both the sender and the receiver are on the ground, the distance will be relatively small. If both stations are in the air, the distance the signals can travel is much further.

When communicating between a ground-based station like Air Traffic Control and an aircraft, the distance is somewhere in the middle.

To work out the exact distance a VHF signal will travel, you can use the following equation:

VHF signal distance in nautical miles = 1.23 x (√height of transmitting object in feet + √ height of receiving station in feet)

So, with an aircraft at 36,000 feet and the ATC radio tower at 100 feet, communication will be possible up to 250 nautical miles away. However, this is the theoretical optimum and will be much less in practice due to transmitter power and receiver inefficiencies.

Read more : The challenges for pilots when landing at hot and high airports

How pilots use it

Most commercial aircraft will have three separate VHF radios. Not only does this give us backups in case of a failure, but it also allows us to use to a number of different frequencies at the same time.

On the 787, the three VHF radios are identified as "VHF left," "VHF center" and "VHF right." The tuning and control panel (TCP) is — unsurprisingly — used to tune and control all three VHF radios.

VHF-L is used primarily for communications with the active ATC frequency, VHF-C for our datalink and VHF-R to keep a listening watch on the emergency frequency, 12.5.

The TCP gives us two options for each radio -- "active" for the frequency we wish to receive and transmit on and "standby" for a frequency that we would like to have ready to use at the push of a single button.

To tune one of the radios to the desired frequency, we simply type in the numerical part of the frequency using the number keys and hit the key-select button adjacent to where we want the frequency to go. For example, if ATC (on VHF-L) asks us to change to another ATC frequency on 133.65 MHz, we'd type "13365" on the number keys and press the first key-select button on the left-hand side.

When we do this, two things happen.

Firstly, the active VHF-L frequency changes to 133.65 as requested. However, instead of the previous frequency (123.45 in the photo) disappearing from view, it flips across to the SBY column. This is particularly useful in the event that we are unable to make contact with the new ATC unit -- a fairly common event.

Instead of trying to remember the frequency on which we were talking to the previous ATC unit, the TCP has already saved it for us. All we need to do is hit the XFR button and we will be back on the previous frequency. When ready to talk on the frequency, we press one of the three push-to-talk buttons in our seat area and this transmits what we say.

Read more: How pilots operate cargo flights on passenger aircraft

VHF radios are great when flying over areas where there are regular radio towers to send and receive signals. However, when flying over the oceans, VHF comms are not really an option. In these situations where the curvature of the earth prevents the use of VHF, we have to revert to something a little more basic.

Whilst high frequency (HF) radio signals aren't as strong as VHF signals, they are actually able to travel much farther. How?

In the outer edges of the earth's atmosphere, between 37 to 630 miles altitude, is the ionosphere. Here, a shell of electrons and electrically charged atoms and molecules are ionized by energy from the sun. HF radio waves bounce off the ionosphere and back down to earth, enabling them to travel great distances and get around even the biggest of mountains.

During the day, energy from the sun causes the D, E and F layers to become heavily ionized, making the layer more active. At night, with less energy from the sun, only the E and F layers are active. As a result, lower frequencies are better quality during the night and higher frequencies are better during the day.

However, what HF gains in distance, it loses in quality. Quite often, the quality of the signal is so poor that it's impossible for either station to hear each other.

By pressing the HF button at the top of the TCP, we are able to bring up the menu of HF radios. As these are not used as often as VHF radios, there are only 2 HF radios -- left and right.

Tuning the HF radio is exactly the same as the VHF radio. Type in the number, select where you want it to go and it's ready to use. Once again, there is a standby frequency to give us greater flexibility. This is particularly useful when crossing the Atlantic.

Read more: What's happening in the flight deck during a rejected takeoff?

When flying to North America , leaving Irish/Scottish airspace, the controller in Shanwick will give us a primary HF frequency to use and also a backup frequency should the quality of signal be too poor on the primary. They will also give us a primary and backup to contact Gander in Canada when halfway across the Atlantic.

We normally put the primary frequency as the active on HF-L and the backup as the active on HF-R. We then put the primary Gander frequency in the standby for HF-L and the backup in the standby for HF-R, ready to use when needed.

By setting them up in this configuration, we are able to try and contact Shanwick using both the L and R radios at much the same.

With the lack of VHF comms over oceans and the unreliability of HF, what we really need is a way of communicating with ATC without the need to physically speak to them. CPDLC -- the controller pilot data link communications -- is a form of text messaging that enables us to communicate with ATC without the need for voice communications.

When out of VHF coverage, the CPDLC system uses satellites to connect with ATC units on the ground. ATC can then use this to send us instructions relating to changes in our altitude , heading, speed and radio frequencies.

We can also send requests to ATC should we wish to change altitude or change our course to deviate around thunderstorms .

Flying over the Atlantic, CPDLC is used as a primary means of communication with HF as a backup. When flying over land, it is used in conjunction with normal VHF communications.

The CPDLC system is designed for simplicity. To set the system up, we must first log on to the ATC unit we wish to connect to. Each unit has its own four-letter code, which we enter into the login page. For example, London is EGTT .

Once logged on, ATC is able to send us instructions via CPDLC messages instead of making a radio call. This reduces the volume of calls on the radio frequency and also reduces the chance of a misunderstanding.

When receiving a CPDLC message from ATC, for example, a clearance to climb to a higher altitude, it pops up on a screen to the right of the PFD. To reply to the message, we simply press one of the three buttons in the flight deck -- accept, cancel or reject.

To send a message to ATC, we use one of the preset pages in the CPDLC menu.

When crossing the Atlantic, we must get clearance from the controllers on the ground. In days gone by, this exchange would have been done by voice over HF radio. However, with a lack in clarity of transmissions, this process was time-consuming and errors were easily made.

By using CPDLC, the exchange with ATC is much quicker and far less prone to mistakes. We simply fill in the boxes with the required information and hit the send button -- very much like filling out a form on a web browser.

Read more: Flying the length of Africa: London to Johannesburg from the pilot's perspective

The simplicity of CPDLC is also of great benefit in emergency situations. Should the need to divert arise mid-Atlantic, getting hold of ATC on HF could be a laborious process. Instead, in seconds, we can send an emergency report to ATC with all the details they will need to know.

SATCOM, or satellite communications, enable us to make voice calls similar to using a mobile telephone. Using the INMARSAT system, a network of 13 geostationary satellites, we are able to make and receive calls from almost any location in the world.

Calls are initiated by either using pre-assigned short code numbers or using direct dial numbers using a country code and phone number. The call is beamed up to the INMARSAT network and then routed to a ground base station. From here, it is then connected to the intended recipient.

The SAT button on the TCP brings up the SATCOM menu as seen in the photo below. From here we have access to a directory of numbers just like in the contacts on your phone.

To make a call, we simply select the number we wish to dial and hit the "make call' button. We then hear a ringing tone before the person at the other end picks up. There is often a small time delay when making a SATCOM call. As a result, it's essential that we speak slowly and allow time for the other person to hear all of what we've said.

SATCOM is useful when it comes to operational calls but invaluable when a passenger becomes ill during the flight .

Most airlines have access to a service called Medlink . Wherever we are in the world, we are able to call directly to a hospital in Tucson, Arizona. Here, specially trained doctors are able to assess, diagnose and prescribe treatment for a sick passenger. If the situation is serious, they can advise us that a diversion to land at a nearby airport would be in the best interests of the passenger.

The clarity and speed of the SATCOM call mean that a sick passenger can get quality treatment even when five miles above the Pacific Ocean.

Bottom line

Depending on the scenario and geographic location, we have a number of communication channels available to us. VHF is the method we use most of the time, enabling rapid interactions with ATC at times when speed is of the essence like on takeoff and landing.

However, as VHF only works with "line of sight," satellites have enabled us to communicate almost as effectively when in remotes areas via CPDLC and SATCOM. The use of text-based messages also reduces the risk of misunderstandings between ATC and pilots, leading to an increase in in-flight safety.

How does RF signal travel in air?

Electromagnetic radiation travels freely through air, much as it does through a vacuum, as air is not very dense. However, the speed of light through air is slightly reduced.

RF Radiation is simply a specific band or range of Light frequencies. RF travels through air the same way all of the light spectrum does. It is an electro-magnetic wave in "spacetime".

Add your answer:

Can RF signal travel in air medium without antenna?

Yes. An antenna is only used to receive or send a signal. A RF signal travels throughout any air medium independently of the existence or not of an antenna. Of course you will need an antenna if you want to receive the signal (which has to have, by the way, more or less the same lenght of the wavelength of the RF signal), but the propagation of a electromagnetic wave doesn't need a physical support. You can see an example with the radiotelescopes. They receive signals which come from the outer space without any physical support. Electromagnetic waves (and RF signal is one kind of them) doesn't need any physical media to travel (they travel in vacuum too!)

What is resonating frequency?

It is a the RF output of a transmitter that is tuned to a distanced receiver, it have to be in resonance with the transmitter signal to be able to receive the signal

What basic law of electromagnetism explain how an antenna picks up a radio signal?

RF energy is transmitted through an electromagnetic field. Once the field meets the receiving antenna, voltages are produced by using the antenna as a conductor. RF voltages induced by the antenna are passed on to the receiver then reconverted to transmitted RF information.

Can rf can travel in vacuum?

If you mean radio-frequency, yes, all electromagnetic waves can travel in a vacuum.

What travel faster a radio signal or sound in air explain?

Radio signals travel at (essentially) the speed of light, as they are electromagnetic waves like light. Sound waves travel at roughly 1200 km/h. Now you have enough information to answer your own question.

The of an antenna depends upon the frequency of the RF signal and the gain?

The size of an antenna depends upon the frequecny of the RF signal and the gain.

Is rf signal much more important for capturing or not?

rf is must for modulation and demodulation.

What is the purpose of carrier signal in modulation?

Carrier signal is of high frequencies, it gives strength to the original signal because original signal cannot travel long distances so it needs to be strengthen a bit for transmitting. The carrier signal is a high frequency signal, called an RF. Radio Frequency signal, it is to high for the human or animal ear to detect it, so its outside the audible spectrum and can easily be transmitted over the air to receivers that is tuned to receive that frequency and detect any modulation on that signal.

Is an rf power amplifier useful in the home?

The answer to whether an RF power amplifier is useful for your home depends on the qualifty if your equipment. If your T.V. is getting a weak signal for example, an RF power amplifier may be useful to get a better signal.

Where can one obtain an RF signal generator?

You can obtain a RF signal generator from a variety of locations. You can try your local electronics store. If they do not stock it you can try places such as Amazon or eBay.

What occurs whenever a reflected RF signal combines with the main signal?

It produces a high SWR (standing wave ratio) that limits the maximum RF (radio frequency) output.

How do you stop a satellite signal in a temple?

Microwave Radio Frequencies (RF) does not travel through dense metals. A metal roof would block the signal. If you try to get your position on a GPS inside the temple and cannot, then the satellite signals are blocked.

What is the use detector in wireless communications?

The detector detect the audio signal in the received modulated RF signal, rectify it and filter the RF to ground and pass the pure audio to the next stage

Difference between IF and RF signal?

RF signal is coming from an antenna. So it contains electromagnetic waves. But when the signal is processed using electronics circuits, the range of frequency may not be sufficient. So that RF has to be convert to some other frequency acceptable by the circuit. And IF is the intermediate frequency used for tuning & other purpose.

What is a RF amplifier?

A RF amplifier is a device for electrically amplifying the power of an electrical signal, typically, but not exclusively, radio frequency signals.

How you take signal from sky?

Using an Antenna and Receive RF Chain

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RFID Signals Travel Farther in Air Ducts

Researchers have discovered that ventilation ducts at least triple the distance that radio waves from passive RFID tags can travel inside a building.

The discovery could lead to a new breed of building sensors that use RFID tags to wirelessly transmit data to central monitoring systems without the expense of running wires throughout a building, according to a statement by North Carolina State University .

The wireless sensors could replace today’s climate-control systems that use wired thermostats. In addition, the development opens the door to RFID-based smoke detectors, carbon monoxide monitors, or sensors that detect chemical, biological or radiological agents, according to Dan Stancil, head of the university’s Department of Electrical and Computer Engineering.

Stancil’s research team found that air ducts act as electromagnetic waveguides that boost the communication range of UHF (ultrahigh frequency) radio frequency identification tags. The tags emitted a radio signal that could be picked up by an RFID reader at the opposite end of a 30-meter piece of ductwork; the typical range of an RFID signal over open space is 5 to 10 meters.

This story was originally published in Computerworld ‘s print edition. It was adapted from an earlier version that first appeared on Computerworld.com.

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Earthquake snarls air and train travel in the New York City area

By Megan Cerullo

Edited By Aimee Picchi

Updated on: April 5, 2024 / 4:36 PM EDT / CBS News

An  earthquake  centered in New Jersey and felt across the New York City region on Friday disrupted air and rail travel, with ground stoppages at airports in the New York City area and delays in train service. 

Travel operations were momentarily halted Friday morning with ground stoppages at John F. Kennedy International Airport in Queens and at Newark Liberty International Airport in Newark, New Jersey, with crews working to resume normal air traffic operations. By early afternoon, the ground stoppage at JFK had been lifted. 

Arriving and departing flights in Newark also resumed in the afternoon, but delays averaged roughly two hours,  according  to the Federal Aviation Administration. 

The earthquake, which occurred roughly 10:20 a.m. Eastern time, had either a 4.7 or 4.8 magnitude and was centered near Whitehouse Station, New Jersey, 40 miles west of New York City,  according to the United States Geological Survey.

Newark airport is experiencing average departure delays of 43 minutes, according to flight tracking website FlightAware. Inbound aircraft that are already airborne are delayed by about an hour. Inbound flights that have not yet taken off are being held until 12:30 p.m., according to the site.  

Flights in and out of LaGuardia airport in Queens were also delayed, likely in order for airport staff to check for damage to the airport and runways and clear away any debris. 

The ground stoppages and delays are not expected to last long. 

Additionally, New Jersey Transit said it's experiencing up to 20-minute delays across its entire rail service system, in both directions. NJ Transit said it's inspecting a bridge for damage to ensure train travel is safe. 

—CBS News' Kris Van Cleave contributed reporting.

Megan Cerullo is a New York-based reporter for CBS MoneyWatch covering small business, workplace, health care, consumer spending and personal finance topics. She regularly appears on CBS News Streaming to discuss her reporting.

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Delta Air Lines (NYSE: DAL) today reported financial results for the March quarter and provided its outlook for the June quarter. Highlights of the March quarter, including both GAAP and adjusted metrics, are on page five and incorporated here .

“Thanks to the extraordinary work of our 100,000 people, Delta is delivering the best operational reliability in our history, and we have widened the gap to our competitors. We were thrilled to recognize their efforts with $1.4 billion in profit sharing payouts during the quarter,” said Ed Bastian, Delta’s Chief Executive Officer.

"For the March quarter, we delivered record revenue on outstanding operational performance, enabling strong earnings growth. We anticipate continued strong momentum for our business, and in the June quarter, we expect to deliver record revenue, a mid-teens operating margin and earnings of $2.20 to $2.50 per share. We remain confident in our full year targets for earnings of $6 to $7 per share and free cash flow of $3 to $4 billion."

March Quarter 2024 GAAP Financial Results

• Operating revenue of $13.7 billion
• Operating income of $614 million with an operating margin of 4.5 percent
• Pre-tax income of $122 million with a pre-tax margin of 0.9 percent
• Earnings per share of $0.06
• Operating cash flow of $2.4 billion
• Payments on debt and finance lease obligations of $712 million
• Total debt and finance lease obligations of $19.4 billion at quarter end

March Quarter 2024 Adjusted Financial Results

• Operating revenue of $12.6 billion, 6 percent higher than the March quarter 2023
• Operating income of $640 million with an operating margin of 5.1 percent
• Pre-tax income of $380 million with a pre-tax margin of 3.0 percent
• Earnings per share of $0.45
• Operating cash flow of $2.5 billion
• Free cash flow of $1.4 billion
• Adjusted debt to EBITDAR of 2.9x, down from 3.0x at the end of 2023
• Return on invested capital of 13.8 percent on a trailing five quarter average, up 2.8 points over prior year.

Read the full release on  PR Newswire  or via  download .

Forward Looking Statements

Statements made in this press release that are not historical facts, including statements regarding our estimates, expectations, beliefs, intentions, projections, goals, aspirations, commitments or strategies for the future, should be considered “forward-looking statements” under the Securities Act of 1933, as amended, the Securities Exchange Act of 1934, as amended, and the Private Securities Litigation Reform Act of 1995. Such statements are not guarantees or promised outcomes and should not be construed as such. All forward-looking statements involve a number of risks and uncertainties that could cause actual results to differ materially from the estimates, expectations, beliefs, intentions, projections, goals, aspirations, commitments and strategies reflected in or suggested by the forward-looking statements. These risks and uncertainties include, but are not limited to, the possible effects of serious accidents involving our aircraft or aircraft of our airline partners; breaches or lapses in the security of technology systems we use and rely on, which could compromise the data stored within them, as well as failure to comply with evolving global privacy and security regulatory obligations or adequately address increasing customer focus on privacy issues and data security; disruptions in our information technology infrastructure; our dependence on technology in our operations; increases in the cost of aircraft fuel; extended disruptions in the supply of aircraft fuel, including from Monroe Energy, LLC (“Monroe”), a wholly-owned subsidiary of Delta that operates the Trainer refinery; failure to receive the expected results or returns from our commercial relationships with airlines in other parts of the world and the investments we have in certain of those airlines; the effects of a significant disruption in the operations or performance of third parties on which we rely; failure to comply with the financial and other covenants in our financing agreements; labor issues; the effects on our business of seasonality and other factors beyond our control, such as changes in value in our equity investments, severe weather conditions, natural disasters or other environmental events, including from the impact of climate change; failure or inability of insurance to cover a significant liability at Monroe’s refinery; failure to comply with existing and future environmental regulations to which Monroe’s refinery operations are subject, including costs related to compliance with renewable fuel standard regulations; significant damage to our reputation and brand, including from exposure to significant adverse publicity or inability to achieve certain sustainability goals; our ability to retain senior management and other key employees, and to maintain our company culture; disease outbreaks, such as the COVID-19 pandemic or similar public health threats, and measures implemented to combat them; the effects of terrorist attacks, geopolitical conflict or security events; competitive conditions in the airline industry; extended interruptions or disruptions in service at major airports at which we operate or significant problems associated with types of aircraft or engines we operate; the effects of extensive government regulation we are subject to; the impact of environmental regulation, including but not limited to regulation of hazardous substances, increased regulation to reduce emissions and other risks associated with climate change, and the cost of compliance with more stringent environmental regulations; and unfavorable economic or political conditions in the markets in which we operate or volatility in currency exchange rates.

Additional information concerning risks and uncertainties that could cause differences between actual results and forward-looking statements is contained in our Securities and Exchange Commission filings, including our Annual Report on Form 10-K for the fiscal year ended December 31, 2023. Caution should be taken not to place undue reliance on our forward-looking statements, which represent our views only as of the date of this press release, and which we undertake no obligation to update except to the extent required by law.

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Delta Air Lines posts a narrow Q1 profit and says travel demand remains strong despite flight scares

FILE - A Delta Air Lines plane lands at Logan International Airport, Jan. 26, 2023, in Boston. Delta reports earnings on Wednesday, April 10, 2024. (AP Photo/Michael Dwyer, File)

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Delta Air Lines eked out a narrow first-quarter profit and said Wednesday that demand for travel is strong heading into the summer vacation season, with travelers seemingly unfazed by recent incidents in the industry that ranged from a panel blowing off a jetliner in flight to a tire falling off another plane during takeoff.

Delta reported the highest revenue for any first quarter in its history and a $37 million profit. It expects record-breaking revenue in the current quarter as well. The airline said that second-quarter earnings will likely beat Wall Street expectations.

CEO Ed Bastian said Delta’s best 11 days ever for ticket sales occurred during the early weeks of 2024.

If travelers are worried about a spate of problem flights and increased scrutiny of plane maker Boeing , “I haven’t seen it,” Bastian said in an interview. “I only look at my numbers. Demand is the healthiest I’ve ever seen.”

A slight majority of Delta’s fleet of more than 950 planes are Boeing models, but in recent years it has bought primarily from Airbus , including a January order for 20 big Airbus A350s. As a result, Delta will avoid the dilemma facing rivals United Airlines and American Airlines, which can’t get all the Boeing planes they ordered. United is even asking pilots to take unpaid time off in May because of a plane shortage.

“Airbus has been consistent throughout these last five years (at) meeting their delivery targets,” Bastian said.

Delta does not operate any Boeing 737 Max jets, the plane that was grounded worldwide after two fatal crashes in 2018 and 2019, and which suffered the panel blowout on an Alaska Airlines flight this year. However, the Atlanta-based airline has ordered a new, larger version of the Max that still hasn’t been approved by regulators. Bastian said Delta will be happy to use the Max 10 when they arrive.

While Delta has largely dodged headaches caused by Boeing, it faces other obstacles in handling this summer’s crowds.

Delta is lobbying the federal government to again allow it to operate fewer flights into the New York City area. Otherwise, Delta could lose valuable takeoff and landing slots.

The Federal Aviation Administration granted a similar request last summer and even extended it until late October . The FAA said the relief helped airlines reduce canceled flights at the region’s busy three main airports by 40%.

Peter Carter, an executive vice president who oversees government affairs, said Delta and other airlines need another waiver permitting fewer flights this summer because the FAA still doesn’t have enough air traffic controllers.

“Absent the waiver, I think we would have, as an industry, some real challenges in New York,” Carter said.

Airlines for America, a trade group of the major U.S. carriers, is also pushing for a waiver from rules on minimum flights in New York. The FAA said it would review the request.

Delta customers will see another change — a new system for boarding planes . Instead of boarding by groups with names such as Diamond Medallions, Delta Premium Select and Sky Priority, passengers will board in groups numbered one through eight. The airline says it will be less confusing.

“When you have a number and you’re standing in line, we are all trained to know when it’s our turn,” Bastian said.

The change won’t alter the pecking order of when each type of customer gets to board. Those with the cheapest tickets, Basic Economy, will still board last.

Delta’s first-quarter profit follows a $363 million loss a year ago, when the results were weighed down by spending on a new labor contract with pilots.

“We expect Delta to be one of the few airlines to report a profit in the March quarter,” TD Cowen analyst Helane Becker said even before Delta’s results were released.

Delta said that excluding special items, it earned 45 cents per share. Analysts were expecting 36 cents per share, according to a FactSet survey.

The airline forecast second-quarter earnings of $2.20 to $2.50 per share. The Wall Street consensus was $2.22 per share. The company stood by its forecast of full-year earnings between $6 and $7 per share.

First-quarter revenue rose 8%, to $13.75 billion. Putting Delta’s Pennsylvania refinery aside, operating revenue was slightly more than analysts predicted. The airline said second-quarter revenue will be 5% to 7% higher than a year ago.

The airline reported that large corporate customers — who were slower than leisure travelers to resume flying after the coronavirus pandemic — are spending more on travel, including firms in technology and financial services.

Delta has boosted profit by focusing more on premium passengers who pay the highest fares, and raking in money from a credit-card partnership with American Express.

Costs could rise too, however. Jet fuel is higher than it was a year ago, following a run-up in oil prices, and Delta is spending more on aircraft maintenance this year.

Shares of Delta Air Lines Inc. fell 2.3% by the end of regular trading Wednesday.

Travel could be a good deal this summer. Here's when plane ticket prices will peak.

Spring is springing and according to Hopper, it’s time to start thinking about your summer vacation plans.

New data from the online booking site shows some favorable trends for travelers in the next few months, including slightly lower airfares compared to 2023, and hotel and car rental prices that are more or less flat year-over-year.

Here’s what you need to know as you prepare to book, whether you’re looking to take a domestic getaway or go on an overseas adventure. It’s also not too late to take advantage of deals on some last-minute trips.

How much are spring and summer plane tickets?

According to Hopper, the best deals right now are on domestic airline tickets. Round-trip flights within the U.S. are averaging $290 in April, but prices are expected to rise in the months ahead.

Hopper’s data shows prices for domestic flights will peak between May and June at $315 on average, and then will gradually fall through the summer, reaching a low of $264 on average in September.

On a call with investors discussing first-quarter earnings Wednesday, Delta Air Lines CEO Ed Bastian said summer travel demand has been pushed forward in recent years due in part to schools, especially in the South, finishing their summer breaks earlier in the year.

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This summer will also be a good time to travel internationally, with Hopper data showing fares to most destinations abroad down compared to last year. 

“Airfare to international destinations continues to improve following two years of bloated prices due to quickly recovering demand, high fuel prices and supply constraints. Airfare to most major regions of the world has dropped compared to last year with the exception of trips to Canada,” Hayley Berg, Hopper’s chief economist, said in the report. “International fares remain higher than pre-pandemic levels to most regions, as higher fuel prices persist and airlines continue to rebuild capacity to many regions.”

How much will a hotel room for the spring and summer cost?

Hotel prices remain more or less flat compared to the same time last year. Rooms in the U.S. are averaging $206 per night currently, with even better deals available in some trending international destinations like Osaka, Japan and Istanbul, Turkey.

According to Hopper, Las Vegas, New York and Chicago remain popular destinations in the U.S.

Will car rental prices go up this summer?

Car rental prices also haven’t gone up much since last year, averaging $42 per day currently, according to Hopper.

The report shows that most travelers rent a car for about four days and warm weather destinations like Orlando and Los Angeles remain popular pickup points.

Zach Wichter is a travel reporter for USA TODAY based in New York. You can reach him at [email protected].