How much distance a radio wave can travell? - Page 1
Forum section: electronics / beginners

author: JustAnotherGuy999
author_rank: Contributor
timestamp: February 25, 2016, 08:38:20 pm
content: Is there a relation between the frequency of a radio wave and the distance it can travel?If you have a table or a mathematical formula, it would be helpful

author: Audioguru
author_rank: Super Contributor
timestamp: February 25, 2016, 08:45:06 pm
content: Low frequencies like on the AM broadcast band can bounce off the ionosphere at night and go very far around the curvature of Earth. But FM broadcast band signals are at a high frequency that do not bounce and are blocked by the curvature of earth so they do not go far.

author: BobbyK
author_rank: Regular Contributor
timestamp: February 25, 2016, 08:57:34 pm
content: A radio wave will travel forever, unless it bounces off something (reflection or refraction) or gets absorbed. The problem is in recovering a signal that has traveled too far and is attenuated too much.Absorption depends on a lot of factors, e.g. the molecules in the medium through which the wave is traveling - this e.g. allows for absorption spectroscopy, which can tell you what the composition of a gas is based on the attenuation of light traveling through a gas. When talking about the atmosphere (mostly nitrogen and oxygen) the different layers also come into play (since some are ionized and affect radio waves in dramatic ways). Here is a document that explains absorption, refraction, and reflection in all the layers of our atmosphere:https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&ved=0ahUKEwim8eb-5ZPLAhWJCCwKHZmEBz4QFghMMAg&url=http%3A%2F%2Fwww.haystack.mit.edu%2Fedu%2Fpcr%2Fwaves%2FThe%2520Atmosphere%2FThe%2520Atmosphere.ppt&usg=AFQjCNFsm5apURlCWhLSOmCFRqDr6k2E_g&cad=rjaIn outer space, electromagnetic waves, technically travel forever, however they are attenuated based on the inverse square law, so at large distances, they would be hard to recover. with a big enough radio telescope or optical telescope you can still see some very distant galaxies though, so there is hope

author: JustAnotherGuy999
author_rank: Contributor
timestamp: February 25, 2016, 09:01:47 pm
content: thanks guys (y)

author: HAL-42b
author_rank: Frequent Contributor
timestamp: February 25, 2016, 09:10:53 pm
content: Quote from: BobbyK on February 25, 2016, 08:57:34 pmWe have pohtomultipliers that can detect single photons but we must make sure no stray photons get in the sensor. So the background radiation of the universe becomes the limiting factor because it is always present.

author: Zero999
author_rank: Super Contributor
timestamp: February 25, 2016, 09:11:40 pm
content: The cosmic microwave background radiation has travelled the length of the universe.https://en.wikipedia.org/wiki/Cosmic_microwave_background

author: dom0
author_rank: Super Contributor
timestamp: February 25, 2016, 09:30:08 pm
content: Did they? Or did the space containing them expand, while they were traveling in the same direction (assuming the concept applies)? :-)

author: retrolefty
author_rank: Super Contributor
timestamp: February 25, 2016, 10:07:37 pm
content: Quote from: JustAnotherGuy999 on February 25, 2016, 08:38:20 pmClosest thing I can think of is crude calculations for line of sight estimation for setting antenna height for desired coverage. That applies to UHF/VHF/microwave. I know that microwave links have to budget in fog absorption for certain areas by using more power then otherwise a specific link requires, but I don't recall the DB margin used.

author: Renegade
author_rank: Regular Contributor
timestamp: February 26, 2016, 02:57:25 am
content: There is some basic information here:https://en.wikipedia.org/wiki/Radio_frequency#Frequency_bands

author: Zero999
author_rank: Super Contributor
timestamp: February 26, 2016, 08:47:17 am
content: Quote from: retrolefty on February 25, 2016, 10:07:37 pmI believe the bandwidth is the determining factor here. The more bandwidth required, the greater power required.

author: DimitriP
author_rank: Super Contributor
timestamp: February 26, 2016, 11:17:53 am
content: Well, I don't know if you typed what you thought you meant or meant what you typed but the distancea radio wavetravels is exactly one wavelength.https://en.wikipedia.org/wiki/WavelengthNow if you manage to string together a bunch of those at high enough power....they can go on and on and on and on ...the page below although it talks about Earth-Moon-Earth communication, it does include loss calculationshttps://en.wikipedia.org/wiki/Earth%E2%80%93Moon%E2%80%93Earth_communication