earthsci said:
LOL.....I don't want to dim your bulb too much here, but radio signals do travel farther at night.
Radio waves naturally travel in straight lines, so you would naturally expect (because of the curvature of the earth) that no radio station would transmit farther than 30 or 40 miles. And that is exactly the case for ground-based (as opposed to satellite) TV transmissions. The curvature of the earth prevents ground-based TV transmissions from going much further than 40 miles (64 km). Certain radio stations, however, especially in the short-wave and AM bands, can travel much farther. Short-wave can circle the globe, and AM stations transmit hundreds of miles at night.
This extended transmission is possible is because of the ionosphere -- one of the layers of the atmosphere. It is called the ionosphere because when the sun's rays hit this layer, many of the atoms there lose electrons and turn into ions.
As it turns out, the ionosphere reflects certain frequencies of radio waves. So the waves bounce between the ground and the ionosphere and make their way around the planet. The composition of the ionosphere at night is different than during the day because of the presence or absence of the sun. You can pick up some radio stations better at night because the reflection characteristics of the ionosphere are better at night.
Link
I don't think so!!!
I don't know who wrote that article, but it contains a lot of half-truths and a mish mash of differing concepts.
I was a microwave specialist in the army. I spent a full year at Ft. Monmouth, Red Bank, N.J. studying electricity, microwave communications and a specialized form of it called tropospheric scatter.
The initial part is right. VHF and UHF frequency communications (radio and tv waves) ARE what is commonly termed LOS or Line of Sight communications, and indeed have a normal limit of the stated 30-40 mile range. Those standard waves do not depend upon reflection from the ionosphere or troposphere for their primary propogations and receiving.
That is part of why all long distance telephone communications for so many years, and even still today, are carried by microwave. Even standard microwave tranmission is still line-of-sight. That's why you see the "dishes" or "towers" on mountain or hill tops, just like standard radio transmitters.
Tropospheric scatter is where a super powerful beam is bounced off the troposphere and back to earth then picked up. But that takes not only sophisticated, and superpowerful transmitter to generate the initial beam, but also super, super sensitive specialized receivers to pick the reflected beam up...because so much power is lost in that transmission.
A standard am radio doesn't even come close to being able to do that.
No only for the frequency range itself, but the power needed for the receiver is just not there, among other things.
Like I said, the primary reason you sometimes seem to get better reception at night with some stations is because they have super powerful transmitters.
At sundown, many smaller, weaker, stations that only have enough power to broadcast a limited local range, either cut down on their power at night, and some even go off the air all together.
The big powerful stations, like KFBK out of sacramento, who I used to listen to Giant games at night, I could only get in Washington after dark.
But that was because the stations like that actually often boost up their power output at night.
I believe, but it's been so long, I'm not totally sure, but the FCC limits how much power can be used during the day, and a stations license limits how much power it can use, by its "class", just like in Bars....what class of license they have determines what beverages they can sell.
So its more a combination of increased power to the "Big" stations that try to jack up their power at night, when the regulations lessen and there are less competing stations on bordering bandwith frequencys.
Have none of your ever experienced not only the fading at times in those situations, but also one station "crowding in" on another too. Your listening to the Giant game and suddenly your hearing Vivaldi from some classical station?
Modern day communications have now gone to satellite reflection rather than tropospheric scatter, in many cases.
But plain old LOS radio signals do not rely much, if any, on reflected beams for their transmission. There may be some, but its far from the primary signal path. At least enough so the "better reception at night" is more a matter of power usage and sharing or competition than some nebulous, "ionospheric reflection".
