How far do OUR radio signals travel ?

toymaker · Mar 23, 2005

When reading the newest SETI announcement a question has formed in my mind : How far do our(human created) radio signals travel to be identified as artificial ? I have heard that only pulses from military radars reach the nearest stars and that is it ?

mooware · Mar 23, 2005

How far signals travel depends upon how much power your using to send out the signal.

holmec · Mar 23, 2005

I disagree. It depends on who is listening and how much power they have to receive a radio wave. As well as the distance, power of trasmission, and obsticles in the way. Otherwise, theoretically, a radio wave can travel farther than we know. <div class="Discussion_UserSignature"> "SCE to AUX" - John Aaron, curiosity pays off </div>

toymaker · Mar 23, 2005

I am asking not about possible transmissions but about the transmission made currently by existing sources of radio waves -radio stations, television, military radars, sattelite communication etc.

vogon13 · Mar 23, 2005

My take on it is: Some signals do not make it out of earths' ionosphere (mostly the low frequency stuff like long wave, and AM broadcast band, suspect US Navy VLF submarine radio also) Many frequencies that do penetrate the ionosphere, are regionally recycled. Like, for instance Disco 99 in Milwaukee, and Solid Gold Oldies in Omaha are on the same frequency, but do not interfere in each others markets because of distance. Away from the earth, in certain directions, a reciever will pickup both stations, and they will interfere with each other enough to make the sound garbled. Many terrestrial transmitters attempt to broadcast the majority of their signal in the direction of the horizon with as little as possible directed upwards. This is the 'gain' of the antenna. It makes the signal stronger in the direction of the listeners and weaker where there are no listeners. Presumably, quite a bit of the signal in this case will be absorbed before reaching space. The rotation of the earth causes most of the signals that do escape earth to sweep around the celestial sphere (like a lighthouse). A distant reciever may not be in the beam long enough to 'lock on' to the signal. Many, many devices emit radio signals. Even some devices that do not need to, do it as a by product of their operation. Like electric motors and electric fence chargers. Many devices also emit radio signals deliberatly, like cordless phones, door openers and such. From a great distance, no individual signal would be intelligible, but you would note a great many total radio waves altogether. Picking up radio signals is a function of distance, the physical size of your antenna, the sensitivity of your radio receiver, and the 'background noise' competeing with the desired signal. In space, extremely large dish antennas maybe possible to construct, so this negates the distance problem. It may be possible to build dishes with diameters of kilo <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

toymaker · Mar 23, 2005

"Earth (taken as a whole)emits more energy at radio wavelengths than the sun does. It is possible aliens, if motivated, would be able to detect this characteristic of our solar system from vast distances (after allowing for the time signals take to reach them)." What about this vast distances ? How far would signals go to be reckognised as artificial-meaning not being dispersed in space ? Is there a certain radius of light years within which it is possible and going further the chance diminishes ? And if so how large is this radius ?

Saiph · Mar 23, 2005

Distance does nothing to blur and ruin signal integrity. It's interfering things that do, and that, I'm not sure. Otherwise, it's a matter of time, Radio has been around in significant strength for less than 100 years (IIRC). So that's about 100 lightyears distance and we "can" be picked up. depending on the intervening material, the signal may be degraded (noise sources) not because the signal is ruined, but because it's to weak compared to the level of noise. Like how it's hard to hear people during a concert. Their words are reaching your ear unaltered. It's just drowned out by the background. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

toymaker · Mar 23, 2005

"Distance does nothing to blur and ruin signal integrity. It's interfering things that do, and that, I'm not sure. " Oh but with distence, don't do the interefences pile up ? (just asking-i am a complete amatour and no little about physics <img src="/images/icons/smile.gif" /> )

Saiph · Mar 23, 2005

Generally yes...if there are more things to interfere. The further you go, the more sources of noise there will be (as they are distributed around in space). I was just pointing out that it's not distance itself that does the degrading. As for how far it can go, it really can depend on which way you're looking. Optical signals for instance, can't be seen by people on the other side of the milky way. They can, however, be seen in andromeda (which is even further). The reason is to cross the milky way you pass a lot of material that absorbs optical light, and emits in the optical as well. Heck, in the optical the sun alone will blind casual observation. You can, however, find ways to get around a lot of noise sources, so technique is an issue as well. In the radio, we outshine the sun, so alien astronomers will catch that oddity at least. So if they can isolate our star with a radio telescope, they should easily be able to pick up the radio signals. Their ability to do this, depends on the size of the telescope... <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

vogon13 · Mar 24, 2005

While I won't be able to cite a specific reference, IIRC, the staff at the Aricebo dish in Puerto Rico have stated they feel their instrument (the 1000 ft dish and its (I think) 500,000 watt transmitter) could communicate with a copy of itself any where (almost) in our galaxy (or roughly 100,000 lightyears, give or take). I do not recall a specific bit rate being mentioned. I attempted once upon a time, to calculate the possibility of radar detection of alpha centauri by using a steadily descending radio frequency broadcast transmitter, coupled with a narrow band descending frequency reciever that just kept scanning over and over to build up enough signal to get a precise distance to calibrate astronomical 'yardstick'. I'm not too savy with math and didn't get too far. Double inverse square deterioration of reflected beam really degrades signal, too. I was optimistic that the angular size of features seen with earth based radar on Titan would be similar to the angular size of alpha centauri and if you waited 8.6 years you would get a 'ping' with some advanced radar techniques the air force was studying for missle defense (the trick lets you mimic radar pulse vastly more powerful than your transmitters continuous output). I got far enough into math to realize I was not smart enough to get an answer, but was far enough along that it looked orders of magnitude short of possible. I know you didn't ask about radar, but its a fun topic too. <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

paleo · Mar 24, 2005

If there are one trillion technologically advanced intelligences in the Universe the odds are no one is remotely anywhere near picking up our signals. There would have to be quintillions. If a small number like 'a trillion' that's just 10 in each galaxy and every ten billionth or so star in this galaxy. The odds are 'astronomical' that any 2 intelligences would be within range to have any meaningful exchange of signals that didn't take thousands of years for responses.

thalion · Mar 24, 2005

IIRC, only our military radars would be detectable from the nearest stars. The other radio signals are either too weak, or omnidirectional; in any event they couldn't be detected with our current equipment from the nearest star(s).

toymaker · Mar 24, 2005

Nice eddie. Now I will post a question of A:Known solar systems withing that radius B:Chances of habitable planets within that radius C:Chances of civilization occuring that close to Earth <img src="/images/icons/wink.gif" /> As you may guess I am up to certain conclusions towards the SETI program <img src="/images/icons/wink.gif" />

yevaud · Mar 24, 2005

I used to (but no longer have) a list of them. Instead, here's a document on the 25 stars nearest Earth, and which of them are of (more or less) the right class to possibly support life. Gotta scroll down several pages to see the list. Pretty much anything that's a K, G, or many F, main sequence (class V) stars are probably correct. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

pizzaguy · Mar 24, 2005

Click here <div class="Discussion_UserSignature"> Note to Dr. Henry: The testosterone shots are working! </div>

pizzaguy · Mar 24, 2005

Yea, it's an eye opener. But like you said, if we dump considerable power in (how do you spell it?) Aericebo? - you CAN make some noise that is heard out there. The old inverse square law really gets you when you are talking great distances. But then, I often lament that we just don't "get it" when talking about interstellar distances. <div class="Discussion_UserSignature"> Note to Dr. Henry: The testosterone shots are working! </div>

Saiph · Mar 24, 2005

I barely get it, and I deal with it all the time. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

siarad · Mar 25, 2005

The Earth here is rotating at about 600mph so a MASER beam would shoot past any listener a few light years away so fast as to be un-noticed, like the beam of a lighthouse or am I confused.

CalliArcale · Mar 28, 2005

If the beam were to fortuitously sweep past a planet inhabited by an advanced civilization, the Earth would resemble a rather slow microwave pulsar if it were emitting such a beam. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

serak_the_preparer · Mar 29, 2005

Good to see Von Konsky's site reappear on these boards - it especially merits a place on the SETI forum (though Space Science is also a good home for it). For me, when all the calulations are done and the problems explained, the line near the end says it best: 'Either way, humanity will have to be very lucky if current SETI strategies are to be successful, even if the Galaxy is teaming with intelligent life.'

nexium · Mar 29, 2005

I think vogon (page 1) has it about right. The last paragraph however may be deceptive: Humans likely send less energy into space on most channels than the Sun does. The other planets, especially Jupiter generate lots of radio noise. Our sun does rotate about the same speed as Earth. I don't think we know the rotation rate of most stars. It is likely that The ISS = the international space station or space shuttle would rarely get a good picture on any TV channel with the equivelent of a dipole outside the craft. At a millionth of a light year = 6 million miles, a very large antenna and a lot of searching of frequencies would be needed to determine that sentient beings live on Earth. Radar pulses are received typically for seconds, rather than minutes, so they would be evidence, but not proof of sentience. Identical repeats would be random and rare. Neil

Saiph · Mar 29, 2005

the sun takes days (nearly a month) to rotate. And it's actually pretty easy to know the rotation rate of stars, and while it isn't a figure often sought after, it is easily obtained. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

cosmictraveler · Apr 11, 2005

If you "aimed" the signal at any object, wouldn't that object move during the time it would take in order to hear the signal? So if we sent a signal to the closest object, we would have to take into consideration the movement of everything during the 10 light years or however long and calculate where the object will be in 10 light years not where it is now. Is that what is being done? How much energy would be needed in order for an object 10 light years away be needed in order to hear our signal? That is if they are listening to that frequency of course. <div class="Discussion_UserSignature"> It does not require many words to speak the truth. Chief Joseph </div>

s3r3n1ty · Dec 3, 2006

i watched a program. they all travel. our broadcasts reach the nearest stars 4 years after they were transmitted our oldest signals, broadcast in the 1920s have traveled past 100,000 stars in our galaxy. anything beyond this point (75 light years) nobody would have any idea of our existence - based on radio waves. *s*

search · Dec 3, 2006

Actually the oldest signals are a bit older than that. 1920 was the first commercial broadcast but 23 years earlier in 1897 was established the world's first radio station on the Isle of Wight, England. The question is not how far did our signals travel but how far did our convenient signals travel. The problem for searching electromagnetic signals is that there is a pleiade of them and it is necessary to narrow down the search and that goes for someone on the other side. From: http://www.bigear.org/guide.htm "There is a portion of the radio spectrum that is relatively quiet from naturally occurring noise from stars and the atmosphere. This is called the radio quiet region. Additionally, within this region there is a portion of the radio spectrum known as the "water hole", from 1420 Megahertz (the emission wavelength for neutral hydrogen) to 1638 Megahertz (the emission wavelength for the hydroxyl radical). This region is called the "water hole" because when hydrogen and hydroxyl are combined, they form a molecule of water. Some people believe that an extraterrestrial civilization might choose this region to broadcast a message, especially if they are a life form based on water like us. They might choose to broadcast in this region, hoping that we would be thinking along similar lines." An alien message would also most likely be what we call a narrowband signal. This means a signal at a very precise frequency. Radio stations are examples of narrowband signals. Between radio stations you hear a hissing sound. This is broadband noise. The stars (and other celestial objects) also put out broadband noise. An intelligent, communicating civilization would probably use a narrowband signal rather than a broadband one for a beacon, since they wouldn't want their message to be mistaken for regular, ordinary star noise."

How far do OUR radio signals travel ?

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