Questions tagged [radio]
The radio tag has no usage guidance.
248 questions
0
votes
0
answers
40
views
AM radio over rainforest
Where can I find information about the AM radio reception at tropical rainforest environment?
Here in Colombia exists one of the most humid environments on the planet.
I can't find information about ...
- 1
3
votes
3
answers
152
views
Optical beating
I wonder why in the systems where two optical signals are combined in a way they produce the beating, the photodiode or any other type of detector relying on the photon absorption is used. For example,...
- 31
-1
votes
1
answer
86
views
The 3.7 m dish antenna of Voyager
I need to know how Voyager-I was able to communicate with the base station on earth using the 3.7m dish antenna? Usually any dish antenna needs to be pointed towards the receiver and Voyager must be ...
15
votes
7
answers
3k
views
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 ...
- 161
140
votes
2
answers
72k
views
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 ...
- 7,142
1
vote
2
answers
148
views
Radio waves: physical mechanism of ground (surface) wave propagation
Radio waves with frequencies below ~3 MHz can propagate as ground waves, following the curvature of the Earth to reach distances well beyond the visual horizon. However, I am confused about the ...
- 205
0
votes
2
answers
110
views
Book Recommendation about radio frequency antennas and satellites
I have recently obtained a job in the field of radio frequency antennas and satellites, and I am interested in delving deeper into the subject. Could you recommend any books that cover these topics ...
0
votes
2
answers
46
views
How strength of RF coupling depend on the antenna material?
If we place different materials in the microwave owen, they will get hot at different speeds. For instance meals get hot really fast. What material property decides on the strength of the coupling? ...
- 1
3
votes
3
answers
2k
views
The Journey of an Electromagnetic Wave Exiting a Router
I'm learning a bit of how WiFi works under the hood, and have a basic grasp of the general process.
First, you make an internet request. Your computer then sends out a WiFi signal which your router ...
- 151
1
vote
1
answer
66
views
If the speed of light is a constant value and the wavelength is constant (antenna), how can one antenna transit/receive different frequencies?
The speed of light is about 300,000,000 m/s, and the wavelength is determined by the design of the antenna, how can one antenna transmit different frequencies other than just the one defined by
f = c /...
- 13
0
votes
1
answer
137
views
What's wrong with solar wind?
As you know, the sun emits into the surrounding space the so-called "solar wind", consisting of plasma. In turn, plasma is a mixture of charged particles.
According to the laws of physics, ...
- 151
6
votes
3
answers
788
views
Impedance at Feed Point and End of Antenna
Watching this pretty great video from 1947 about antenna fundamentals. I have a question about one part of it though.
The video states that the impedance at the feed point of the antenna is 72 ohms, ...
- 111
2
votes
2
answers
457
views
How does radio wave get reflected?
Actually recently I posted a question in h-bar ($\hbar$) relates to radio wave reflection from mirror, and one of the user replied that it can't, only ionosphere can reflect it, so my question what is ...
- 768
0
votes
1
answer
371
views
Can I use a radio to light a fluorescent light bulb?
I am trying to recreate the demo in this video, titled “How to create your own aurora.”
To summarize the video, a radio is used to light a fluorescent light bulb. The narrator describes the walkie ...
- 1
17
votes
4
answers
3k
views
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) ...
- 317
0
votes
1
answer
156
views
How does an extension cord on a radio apparently function as a reception antenna if placed in certain positions?
I have an old radio and the antenna broke off at some point years ago. The radio has somewhat poor reception, as the room it's in faces a courtyard or alleyway. I have to position the radio just right ...
- 75
1
vote
1
answer
45
views
Why wireless radios start making buzzing noise when I switch on some electrical appliances?
This question has possibly been asked a numerous number of times already, by many people in many places, but nowhere can I find a precise answer to my precise question.
When I turn on, say a ceiling ...
0
votes
2
answers
186
views
Coaxial Confusion, what really are unbalanced transmission lines? [closed]
Thanks for clicking on my question.
I do not understand how an unbalanced transmission line works.
Take for instance coaxial cable which is the subject of my confusion.
This confusion arises from the ...
- 35
1
vote
1
answer
54
views
Do ultrasonic motion detectors (like the Arduino sensor) detect small particles like dust when receiving waves? If they don't why is that the case?
This may be a bit of an elementary question but I've recently started studying physics for fun so this has confused me. Do ultrasonic sensors have the capability to detect very small particles like ...
- 11
0
votes
1
answer
43
views
Impossible VSWR reading for inductively loaded telescopic antenna
I am trying to understand how this SWR reading with an antenna analyzer is possible: https://www.youtube.com/watch?v=PeVZFD07-xY&t=231s.
For context in that video a youtuber describes how to ...
1
vote
0
answers
46
views
Easy question regarding RF and ion traps
I saw this interesting video:
https://www.youtube.com/watch?v=d-qTa_7FtAA
In this video, from the 8:55 mark to 11:55, this man explains using unique frequencies for each element(?) with a unique m/z ...
- 315
1
vote
0
answers
27
views
Is there any mathematical model of how does rain & other weather conditions impact the radio link?
I'm looking through UAV radio-communication process and wondering if there are any formulas, describing how does the air pressure and weather itself (rainy & snowy conditions) affect the radiolink ...
0
votes
2
answers
94
views
Radio Wavefront and Photons?
I have some questions related to radio waves, photons and propagation , transmission and reception.
It’s my understanding a radio wave is a changing electrical and magnetic field that travels through ...
- 245
6
votes
1
answer
704
views
Why are radio telescopes in orbit radio telescopes?
We use radio telescopes on Earth because of the atmosphere, right? It blocks the more energetic wavelengths but not radio waves and microwaves. So, since radiation like x-ray and gamma radiation are ...
1
vote
0
answers
88
views
Chemical detector of radio waves?
Since there are molecules in the eye that can detect electromagnetic waves at light frequencies, would it be possible to detect radio waves (longer wavelength electromagnetic waves) biologically / ...
- 111
0
votes
2
answers
295
views
Can radar detect electrical fields?
Can we create a radar image of electrical fields, or this is even possible?
Do we need a detector opposite the emitter or does reflection work?
(see figure.1)
- 75
2
votes
4
answers
2k
views
How are sidebands generated in an AM signal?
I can't understand how sidebands get generated, even after reading this wikipedia page: https://en.wikipedia.org/wiki/Sideband#Amplitude_modulation
This is how I picture Amplitude Modulation in its ...
- 127
0
votes
1
answer
149
views
Using ham radio to communicate with an underground crew [closed]
In "Stranger things 3" Dustin uses a ham radio named Cerebro (an image https://www.reddit.com/r/StrangerThings/comments/fhrdml/will_cerebro_make_an_appearance_in_st4/) stationed on a hill ...
- 13
2
votes
0
answers
374
views
Where does 1/20th of wavelength come from when referring to maximum mesh size that will reflect a radio wave?
In our physics class, we were taught that radio waves would reflect from surfaces even if they have gaps. Example, radio telescopes are made from mesh instead of the solid, or a microwave that has a ...
6
votes
1
answer
428
views
Radio receivers and the loss of electrons
I'm reading Kenn Amdahls book "There are no electrons" to familiarise my self with the magical world of electricity.
Despite Mr. Ahmdahls insistence on the non-existence of electrons, I find ...
- 221
2
votes
5
answers
1k
views
Quantum description of radio antenna
I am trying to form a clearer picture of how a radio transmitter emits waves from a quantum point of view.
The classical description is quite easy: the electrons oscillate in the antenna and, as ...
- 65k
0
votes
2
answers
152
views
Over what distance might this device be able to interfere with car radios?
I've been reading recently about a mysterious and possibly hokey medical device of the 1930s. It was a variable-frequency radio emitter, invented by a Dr. Rife, which was supposed to kill various ...
- 81
2
votes
2
answers
534
views
Is it really true that radios work better in mountaneous region than in cities?
I was recently travelling somwhere with my family. During the journey we had to pass through a mountaneous terrain. My mother suddenly switched on the radio of car and it was so clear. Is this true ...
- 47
4
votes
2
answers
796
views
What *is* Magnetism? [closed]
Short variant: What is Magnetism exactly?
Or, longer variant;
As an amateur science/(hard) sci-fi enthusiast, I'm slowly but surely realizing that Magnetism feels like an "odd-one out" in ...
- 151
2
votes
1
answer
96
views
What is the explanation behind radio shadowing by people?
I called it shadowing but masking may be more appropriate, feel free to suggest a better question title after you read the following.
I have an old clock alarm radio receiver that plays at the center ...
- 3,256
0
votes
1
answer
503
views
What is the most accurate instrument which can be used to measure frequency of radio waves without measuring wavelength and how accurate is it?
I wanted to know if there's an instrument that accurately measures the frequency of radio waves as I'm working on something and I didn't get anything good on web.
- 21
2
votes
1
answer
97
views
Is there no way to bypass greenhouse gasses by converting excess heat to longerwave radiation?
The problem with greenhouse gases, as I understand it, is that they absorb and emit radiation within the thermal infrared range leading to increased temperatures on Earth. According to some sources, ...
- 71
0
votes
0
answers
59
views
What is the gain of an isotropic antenna?
My question is simple:
What is the gain of an isotropic antenna in dBi?
I cannot find a consistent answer on the internet. Some sources define it to be 0dBi and others define it to be 1dBi.
Thanks.
0
votes
0
answers
89
views
Building a radio telescope!
So, I saw recently the idea of a radio telescope and thought how simple they are. So, like any other normal human being, I went on google and searched "how to make a radio telescope" and ...
0
votes
1
answer
730
views
How to explain mobile phone rings inside microwave oven? [duplicate]
So finally tested myself and found: mobile phone rings inside microwave oven.
Microwave oven frequency is 2.5 GHz which gives wavelength of 12 centimeters. Cellular network waves are even longer. Thay ...
- 1,742
0
votes
1
answer
259
views
Need 50Hz detection antenna for reception of AC mains signal
Anyone know how can i design antenna for electric field detection. i m trying to make contactless Ac mains Detector which range is near about 1-mtr long.
my question is about possibility of antenna ...
- 1
1
vote
2
answers
64
views
Would Radio Communications Between Parties Experiencing Time Differently Be Compressed/Stretched
This is a contrived and extreme example that is likely not even possible, but I'm hoping the answer will help me understand something about communications across relative time.
Imagine two individuals ...
- 13
1
vote
0
answers
28
views
Is it possible to filter radio-waves using another radio telescope?
When making an observation using a radio telescope, is it possible to filter out noise coming out from a known source by using another telescope that will focus on that noise source?
By filtering, I ...
- 2,167
1
vote
1
answer
556
views
Do metal objects improve radio signal reception when standing nearby?
I have a watch (Casio G-Shock GW-M5610 ) which can synchronize itself to radio time signals. In my area it uses DCF77 tower, which transmits 77.5 kHz (approximately 3868.3 m wavelength) signal:
The ...
- 111
-2
votes
1
answer
200
views
How to hide radio communications between airplanes? [closed]
I have 2 airplanes and I would like completely hide the communications between them.
There is a possible way that this communications would not be detected by our radio receivers around the world? ...
- 9
0
votes
1
answer
1k
views
Modulation Index of an AM wave
I have been given a question as
RMS value of an RF(Radio Frequency) voltage after amplitude modulation to a depth of $50$% by a sinusoidal voltage is $80$ Volts. Calculate the RMS value of modulated ...
- 172
0
votes
0
answers
94
views
How does Tx Power affect the Free Space Path Loss model?
On this website one can use the FSPL model to calculate the Path Loss. This is typically interpreted online as the theoretical signal strength (in dB) that one may receive (e.g. from some WiFi). ...
- 101
5
votes
1
answer
562
views
Is this a possible derivation of the electromagnetic wave equation?
Some Background:
I've been trying to understand electromagnetic waves, how they travel, and how they're produced. After some Googling and Wikipedia(ing?) I've learned that we use the EM Wave Equations ...
- 268
3
votes
1
answer
291
views
What is “spectral turnover”?
In a paper which deals with the spectra of radio frequency cosmic events, the word “spectral turnover” is used. What is “spectral turnover”?
1
vote
0
answers
26
views
How is VLBI delay calculated, practically?
I’m working on a research project wherein we are trying to solve a problem very similar to VLBI delay. We have two radio receivers, and we know their locations. We also know at what time one receiver ...