Questions tagged [radio]
251 questions
141
votes
2 answers
How many photons are received per bit transmitted from Voyager 1?
As of 2024, according to https://voyager.jpl.nasa.gov/ , Voyager 1 is around one light·day away from Earth and still in radio contact. When Voyager 1 sends messages to Earth, roughly how many photons are (1) transmitted and (2) received per bit?
Craig Gidney
- 7,172
101
votes
4 answers
Can tin foil hats block anything?
This is joked about all the time, but...
Can tin foil hats actually block anything? If they can, what frequencies? Is there any research into tin or aluminum foil and radio blocking or amplifying abilities when shaped into a hat?
If they really…
Status
- 1,038
73
votes
3 answers
How strong are Wi-Fi signals?
My family members dislike the idea of having many devices communicating wirelessly in our house, arguing that the signals have negative effects on our physical health.
I would like to tell them the EM signals are in fact weaker than the light from…
Chong Lip Phang
- 823
66
votes
4 answers
What's the physics behind XKCD #2027 (time between lightning flash and radio wave burst)?
XKCD usually has solid (and often contemporary) science behind it. Lightning Difference, #2027 one says:
Q: What’s that trick for telling how many miles away lightning is?
A: Just count the seconds between the visible flash and the radio wave…
uhoh
- 6,089
33
votes
7 answers
Radio antennas that are much shorter than the wavelength
From my limited experience with ham radio when I was a kid, I expect transmitting and receiving antennas to have lengths that are on the same order of magnitude as the wavelength, and in fact I recall having to mess around to compensate for the fact…
user4552
18
votes
4 answers
Does a radio receiver "collapse" a radio wave function?
Does a radio receiver "collapse" a wave function when listening to a radio broadcast generated via a transmitting antenna?
Background:
There has been much discussion on this forum (here) about the nature of radio waves, photons and quantum…
kdtop
- 327
15
votes
7 answers
Why does the length of an antenna matter when electromagnetic waves propagate perpendicular to the antenna?
The optimum length for a dipole antenna is a multiple of half the wavelength that it is designed to receive or emit. Why is this? If an electromagnetic wave has E in the x-axis, B in the y-axis, and propagates along the z-axis, it will be generate…
user411769
- 161
15
votes
4 answers
Understanding the cause of sidebands in Amplitude Modulation
I've read it many places that Amplitude Modulation produces sidebands in the frequency domain. But as best as I can imagine it, modulating the amplitude of a fixed-frequency carrier wave just makes that "louder" or "quieter", not higher-frequency…
Jason Kleban
- 455
14
votes
2 answers
How does my hand amplify an FM radio signal?
I have a gizmo that broadcasts an FM radio signal from my phone's headphone socket to my car's radio antenna.
Sometimes, there's another station on the same frequency with a stronger signal and my car plays that signal instead. However I've noticed…
billpg
- 856
14
votes
3 answers
Where does background noise go on a radio station?
If you tune a radio to a frequency where there is no station broadcasting, you hear noise. It's pretty loud, just as loud as the music that comes in when you find a station. And yet, when you do find a station and you have good reception, the…
Mason Wheeler
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12
votes
2 answers
Why does a green stoplight interfere with FM radio reception (more than yellow)?
While listening to an FM radio station (frequencies between 88 and 108 MHz) in my car, I've noticed that as I pull up to a red light, there's an increase in the amount of noise. It's very noticeable when I'm listening to a station that's somewhat…
user218481
11
votes
3 answers
How do radio telescopes work?
If I search online for how radio telescopes work, the found articles talk about how RF is on the spectrum, etc, how the parabolic collector is the aperture which contributes to the sensitivity and reflects the signals into the detector at the focal…
Jason Kleban
- 455
11
votes
7 answers
Why are longwave radio towers so tall?
They are often in the hundred meters high. See the wiki link:
https://en.wikipedia.org/wiki/Longwave
Why are they so tall? Because the wavelength is long, so the antenna should also be long? But to transmit in the longwave region, we only need to…
poisson
- 2,185
11
votes
3 answers
Why is this radio telescope's reflector spherical and not parabolic?
This is the Arecibo Observatory in Arecibo, Puerto Rico. Its reflector is spherical, measuring 1,001 ft. in diameter. It is considered the most sensitive radio telescope on Earth, but the fact that its reflector is spherical and not parabolic makes…
Frank Computer
11
votes
1 answer
Why does my body create interference with my clock radio while in bed?
I typically listen to NPR in the morning from a clock radio next to my bed. There are days when just moving my body, even my arm or leg, is enough to cause interference with the radio to dramatically decrease the volume, or it appears as if I lost…
Carlos
- 4,648