This may be a very dumb question, but I was wondering, does amplitude function as a measurement for "strength" for a radio signal?

I know that hertz defines the frequency, which I understand as the part of the spectrum a given signal occupies (which is, if I'm not totally off base, simply a measurement of where in the possible range of wavelengths, that particular wave's wavelength falls).

I know that amplitude is a measurement of the magnitude of change in a wave. So frequency is the distance between peaks, and amplitude is the distance of peak-to-trough. I also know that amplitude is a measurement of strength for sound waves. When I looked it up, amplitude on sound waves are measured in decibels. So far so good. The more amplitude, the louder it is. I can understand that easily from a lay-perspective.

But apparently the unit of measurement for amplitude isn't the same for all waves. I looked on Wikipedia and it says that displacement is the unit of measurement for waves moving through a medium or down a string, which seems to me is measuring a different quality. First, last time I checked sound moved through air, so why is it measured with a different unit than other waves traveling through a medium? I could see how displacement could be an effective measurement of wave strength (the more stuff it moves the stronger it is) but will that correlate to how far the wave will move through the medium? For instance, a sound can be very loud, can travel very far, and not displace a large amount of air. I'm thinking particularly of high frequency sounds, which can travel far, and be very loud, without producing any air compression (a function of air displacement) detectable by the human body. I'm sure the same could be said for any wave moving through a medium.

Clearly there is more than one possible measurement of "strength" for a wave. I think it's very likely I'm confusing myself, but the various definitions of amplitude aren't helping. :) Why are multiple units of measurement needed to define the same quality of various waves?

Now back to radio waves. I basically understood none of what Wikipedia said on radio wave amplitude. Does it still function as a unit of measurement to define strength? If so, how does it work? If two radio signals were being broadcast at the same frequency, say, the one that car radios use, but one is twice the amplitude, how would my car radio translate that? If amplitude isn't an effective measurement of strength, what serves this function for radio waves? I know that when I'm in my car often I can hear two signals on the same frequency but one is dominate and almost completely drowns the other out. I also know that my little iPod FM broadcaster can drown out some stations but not others, so obviously there is a function of radio wave strength independent of frequency, but what is it and how does it work? Is there more than one way to measure strength on radio waves (like there seems to be for waves in a medium)?

From what I remember from many years ago, sound waves are longitudinal waves, while electromagnetic waves are tranverse waves made from two components, the electrical field and the magnetic field, which have a different phase angle. The energy of the EM wave is given by the Poynting vector, which is the vector product of the two waves. So you cannot compare sound waves with EM waves, they are very different. But this comes from long ago and I may be wrong.
Tullio

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This may be a very dumb question, but I was wondering, does amplitude function as a measurement for "strength" for a radio signal?

The simple answer is 'yes'.

As to whether a signal can be usefully 'heard' depends more on how strong the signal is compared to whatever noise and interference there is for the part of the electro-magnetic (radio) spectrum you are listening to. This is called the signal-to-noise ratio.

s@h maximises the signal-to-noise ratio by 'adding up (integrating) over a long time' for a very narrow frequency bandwidth. Also, the Arecibo radio telescope uses a huge receiving dish to collect lots of radio energy over a very narrow beam and very low noise electronics are used. The limit for the noise is pretty much down to the residual noise from the ancient big bang/rebound!


Hope that helps,

Keep searchin',
Martin

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See new freedom: Mageia Linux
Take a look for yourself: Linux Format
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What i would like to ask is that if seti scientists make any allowance in there research for the possibility that , 'just as gravity bends light ' it should do the same for radio waves. There is no way that it can spare radio waves , so that thought is very important when trying to focus the telescopes . Secondly i wonder if they have taken in to consideration that areas of space could have strong magnetic fields which i would think could also have an effect. Taking the above into consideration no one should come to conclusion that there is no intelligent life out there based on not picking intelligent radio signals. Forgive for always bring up gravity and magnetism , its not that i like the staff but it seems all the answers that we need can't be got unless we take the two into account.

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We choose to go to the moon and to do other things, we choose to go to the moon not because its easy but because its hard. kennedy

Radio sets have had a "discriminator" circuit as part of the overall design for many decades now. This circuit allows the radio station to select only the strongest station to listen to. The stronger the unintended station the harder it is to pick it out of the total signal and discard it.

As we hadn't enough mysteries in the radio spectrum here is the latest one:
radio mystery
Tullio

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This signal has not been seen until now because ground-based telescopes did not have the required precision to detect it, team member Michael Seiffert of NASA's Jet Propulsion Laboratory in Pasadena, California told New Scientist.

I thought that ground based telescopes like arecibo should have been more sensitive ,that means ET could be communicating right under our noses .Seti has to get up there ,one possibility is to team up with anther project that is sending some kind of telescope into space and install on it a seti receiver .The results could change our under standing of the universe over night just as hubble did.

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We choose to go to the moon and to do other things, we choose to go to the moon not because its easy but because its hard. kennedy

I am not aware of any project intending to put a radiotelescope in orbit. Radiotelescopes have big antennas, since the radio wavelength is greater than for infrared, optical, UV, X, gamma ray telescopes and so they are big and heavy. Also, since there is a radio window in the atmosphere, you would not gain much in sensitivity. I haven't understood at which frequency/wavelength they have observed this signal.
Tullio

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This article is very interesting. Just going to tag this one here. If it's been posted please delete it.

http://www.foxnews.com/story/0,2933,477880,00.html

Mystery Roar Detected From Faraway Space
Friday, January 09, 2009

By Andrea Thompson

LONG BEACH, Calif. — Space is typically thought of as a very quiet place. But one team of astronomers has found a strange cosmic noise that booms six times louder than expected.

The roar is from the distant cosmos. Nobody knows what causes it.

Of course, sound waves can't travel in a vacuum (which is what most of space is), or at least they can't very efficiently. But radio waves can.

Radio waves are not sound waves, but they are still electromagnetic waves, situated on the low-frequency end of the light spectrum.

Many objects in the universe, including stars and quasars, emit radio waves. Even our home galaxy, the Milky Way, emits a static hiss (first detected in 1931 by physicist Karl Jansky). Other galaxies also send out a background radio hiss.

But the newly detected signal, described here today at the 213th meeting of the American Astronomical Society, is far louder than astronomers expected.

There is "something new and interesting going on in the universe," said Alan Kogut of NASA's Goddard Space Flight Center in Greenbelt, Md.

A team led by Kogut detected the signal with a balloon-borne instrument named ARCADE (Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission).

In July 2006, the instrument was launched from NASA's Columbia Scientific Balloon Facility in Palestine, Texas, and reached an altitude of about 120,000 feet (36,500 meters), where the atmosphere thins into the vacuum of space.

ARCADE's mission was to search the sky for faint signs of heat from the first generation of stars, but instead they heard a roar from the distant reaches of the universe.

"The universe really threw us a curve," Kogut said. "Instead of the faint signal we hoped to find, here was this booming noise six times louder than anyone had predicted."

Detailed analysis of the signal ruled out primordial stars or any known radio sources, including gas in the outermost halo of our own galaxy.

Other radio galaxies also can't account for the noise — there just aren't enough of them.

"You'd have to pack them into the universe like sardines," said study team member Dale Fixsen of the University of Maryland. "There wouldn't be any space left between one galaxy and the next."

The signal is measured to be six times brighter than the combined emission of all known radio sources in the universe.

For now, the origin of the signal remains a mystery.

"We really don't know what it is,"said team member Michael Seiffert of NASA's Jet Propulsion Laboratory in Pasadena, Calif.

And not only has it presented astronomers with a new puzzle, it is obscuring the sought-for signal from the earliest stars.

But the cosmic static may itself provide important clues to the development of galaxies when the universe was much younger, less than half its present age.

Because the radio waves come from far away, traveling at the speed of light, they therefore represent an earlier time in the universe.

"This is what makes science so exciting," Seiffert said. "You start out on a path to measure something — in this case, the heat from the very first stars — but run into something else entirely, some unexplained."