Questions tagged [radio]

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17 views

What modulation is this? [migrated]

I'm currently learning about signal modulation and fail to figure out the modulation of this signal - maybe someone can help me with it? The software is GNURadio and the device capturing the signal ...
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18 views

How to convert user friendly linear antenna power into actual dBm

I need to create a simple UI, where user would select the desired antenna power on a RFID reader. The user would select a linear value on a slider (from 0 to 100) which will then in turn get converted ...
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1answer
20 views

Is the radio attenuation of an obstructed 2.4GHz signal, dependent on its incident power?

The following figure (taken from CTS 115: Free Space Path Loss) describes generally how obstructions attenuate a 2.4GHz signal: I would like to ask, is this -3dB loss dependent on the power (or ...
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1answer
77 views

Is it true that if one stood on Westminster Bridge with a radio, one would hear the chimes of Big Ben via the radio sooner than in the real world?

I was reading this review of Damon Krukowski’s Ways of Hearing in The Spectator when I stumbled across this claim: “And before the renovation of Big Ben began, if you stood on Westminster Bridge ...
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2answers
120 views

How far can radio waves travel in vacuum? and light waves?

Radio wave and light wave are the same thing. They all are electromagnetic radiation, the only difference between them is frequency. My question : 1, is there any photon-like thing for radio wave? 2, ...
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2answers
37 views

Radio wavelength to penetrate 8 ft of seawater

I am trying to penetrate about 8 ft of seawater with a radio wave. What wavelengths will work? I understand that low wavelengths penetrate seawater the best, but I am looking for a frequency that does ...
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1answer
41 views

How to calculate how far radio light goes in the ocean [closed]

Radio light is not a practically useful way of communicating underwater over large distances. My question is how does one calculate how far a radio wave at a given frequency will propaagate in the ...
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3answers
6k views

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 ...
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2answers
27 views

Radio Waves / Light: Atmospheric Refraction

The following image differentiates between a visual horizon and a radar horizon. Sidenote: I'm not too familiar with primary surveillance radar technology, but this image refers to secondary ...
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1answer
94 views

Why was the imaging of M87 black hole easier than imaging the Milky way's Sagittarius A*? [duplicate]

In the recent EHT press release of the image of the super massive black hole at M87, I am curious to know why the super massive black hole at the centre of milky way has not been imaged yet.
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1answer
72 views

Naive question about Analog and Digital Signals

I have just started telecommunications in high school Physics. We are currently studying analog to digital conversion. I have 2 questions : How is a "digital" signal transmitted? As far as I know, ...
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2answers
49 views

How can be various frequencies in one place?

How can we receive different radio shows in one place, they are coded in phase or frequency or amplitude of electromagnetic waves, but shouldnt elecreomagnetic waves interact each other, and all ...
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2answers
92 views

Is it possible to use visible light to transmit “radio” like AM/FM?

When I see a big radio antenna, I like to imagine it's a giant incandescent light bulb filament in the vertical, but of a invisible light. So that it "glows" the radio, performing oscillations which ...
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2answers
507 views

Why does a green stoplight interfere with FM radio reception (more than yellow)? [closed]

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 ...
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7answers
1k views

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 ...
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4answers
125 views

Can we create a 20 Hz EM wave?

The electronic spectrum we study on our textbooks starts from radio waves of an order of kilohertz. But is there a lower limit for EM radiation? Cant we create EM wave of any frequency from minus ...
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1answer
29 views

Why is $Q$ factor an important quantity for electrical oscillations transmitting radio waves?

My textbook says that "$Q$ factor is an especially important quantity for electrical ossicilations trasnmitting radio waves. When selecting radio and television stations it is essential that the ...
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2answers
396 views

Why radio waves from radio-stations don't interfere with each other?

I know that radiowaves from radiostations are modulated either F.M or A.M . Lets suppose they are F.M and one has carrier wave frequency of 100 Hz and other 200 Hz they have F deviation of 20Hz/V . ...
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2answers
174 views

Is this the correct way to apply an inverse square law to radio wave propagation?

This question is vaguely a follow up to this one and this one. If I have a completely flat surface with a radio transmitter with 500 W ($\approx$ 57 dBm) of power, broadcasting on a frequency such ...
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1answer
76 views

Does attenuation to RF waves increases with frequency?

I heard somewhere that RF waves at high frequency such as above 2GHz face more attenuation while passing through air, buildings and due to humidity as compared to 800Mhz and 2) Waves at 30-40GHz ...
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2answers
103 views

How are RF Waves transmitted?

What is the mode of transmission for RF waves at 1800 MHz. Is it ground wave propagation, Line of Sight Propagation or Atmospheric reflection (from ionosphere). What are the different ways for ...
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1answer
53 views

Why is power density of RF waves measured in m2?

Why is power density of RF waves measured in m2 or cm (Area) and not in cm3 or m3 (volume) ? I mean aren't those waves travelling (radiating) in 3D space? I am new to this topic so please pardon ...
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4answers
206 views

How do radiowaves have constructive/destructive interference?

When you have radios you often find interference happening. As far as I am personally aware radio waves are the only waves that I am sure can interfere. If all EM apply do put it in that perspective ...
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1answer
71 views

Why we don't utilize most of the radio or microwave spectrum?

WiFi is from 2400-2500MHz or from 5000-5100. Fm Radio is 87-108Mhz, Phones : 450-3400Mhz But most of the spectrum is "wasted". For eg - Why we don't use above 5Ghz?
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1answer
66 views

Why does a battery powered radio's volume go down as batteries age, even when the batteries' voltage is constant?

A set of batteries are used for a long period of time. Explain why the volume of a radio is low even though the voltage of the batteries is the same as when they were first bought.
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2answers
44 views

Is there a quantifiable tradeoff (in terms of effective broadcast distance) between the height of a radio tower and the power of the transmitter?

I have a dataset on radio stations with the following variables: the power of the transmitter, in watts the coordinates of the radio tower I can easily get the elevation at those coordinates and the ...
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4answers
12k views

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 ...
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1answer
320 views

Radio waves collision versus waves in a pond collision

Please see the attached picture: We are trying to show an image to visualize radio wave collision and interference with regards to Maritime AIS Technology. What do colliding radio waves have in ...
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1answer
40 views

Radio waves and walls

I am new to here. I am not familiar with physics well, but since this question in my opinion does not seem to belong to ELL, kindly pardon me to ask here. When given such a sentence below, radio ...
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2answers
56 views

Can we determine the distance from a radio station (antenna) and a receiver using radio wave ?

say we have the a receiver and radio antenna can we calculate the distance between the receiver and the antenna by a receiver if we know the frequency ?
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3answers
428 views

How did Jocelyn Bell aim her radio telescope (phased array)?

In 1967 Jocelyn Bell discovered pulsars using the Cambridge University radio telescope - a two hectare field of posts and wires. The pulsar was found to be in the constellation Vulpecula. How did ...
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45 views

Radio wave detection timing

Hypothetical: I have a simple LC tuned resonant circuit, with the antenna attached to one end of a tuned parallel LC, and ground to the other, and the results amplified and passed into some kind of ...
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2answers
478 views

Radio wave behaviour in reflection, Refraction and Diffraction

I am trying to understand how radio waves behave when reflected, refracted and diffracted. I have put together a list based on light which I think will be the same. Can anyone tell me the behaviour of ...
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114 views

Why does a radio's tank circuit frequency match the emitted EM wave freqency?

I am trying to understand some of the specifics of RF radiation. I am concerned with the normal antenna-emitted EM waves, no relativistic charges, no Bremsstrahlung involved. The tuning of a tank ...
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1answer
48 views

Radio light/radio wave light: what does this mean?

What is radio light and radio wave light? Is this a term? There is nothing on the internet that goes by this. I need an explanation as to what this term means and why my professor keeps using it. ...
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1answer
56 views

Photon spins from Radio Antennas

I’m a radio amateur (ham). Let us consider a half wavelength horizontal dipole antenna in free space – say at 10MHz and look at its far field. Conventional high school physics says that because the ...
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1answer
352 views

Why can radio telescopes use wire mesh as their parabolic dish?

Radio telescopes use wire mesh to save cost. How does that work? Won't the waves go through the gaps?
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2answers
167 views

What's the maximum distance that a radio wave can travel at full power [closed]

If the sun is eight minutes away if you are travelling at the speed of light, since that's how long it would take for people to notice if the sun had stopped shining, how far can a short-wave radio ...
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3answers
106 views

Trouble in understanding AM modulation

Amplitude modulation is in fact, superimposing the low frequency transmission signal into a high frequency carrier signal, right? So, if the transmission signal can be represented as $c(t)=A_c \sin (\...
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1answer
81 views

Receiving AM radio through household wiring

A friend's post on FB made me recall a similar situation. In his case, his IR-linked headphones now play a local AM station at very low volume whenever he's near an electrical outlet or switch in his ...
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55 views

Magnet on a piezo - Can this oscillating field give me a radio transmitter?

I can read on wikipedia that radio waves are of frequency 3kHz-3THz. I know that piezoelectric actuator can reach eg. 20 kHz. What would happen if I put a small neodymium magnet on a piezoelectric ...
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1answer
79 views

Nuclear Reactor Meltdown vs Radio Waves

So my lecturer was discussing the use of robotics to deal with the fallout from either decommissioned nuclear reactors or reactors that have gone into meltdown (the example here being Fukushima). Of ...
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1answer
60 views

Why tilting a radio makes it play?

I was helping my mother in making her radio play. There was no technical issues with the radio, but it would go crazy when a nearby tubelight was switched on. We tried many things, adjusted the ...
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1answer
106 views

How do Antennas receive information?

Do wireless signals (Wifi router, radio, telephone) send their information in single "blinks" or in a continuous wave with frequency modulation or Amplitude modulation? If a radio for example needs ...
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2answers
715 views

Attenuation of radio frequency transmissions in space

In a science fiction movie some aliens come to earth and when asked why, they say they received our radio transmission and came to investigate, the radio transmission being the first television ...
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1answer
52 views

Why do regulations exist for radio broadcasting?

I've heard many times said as an argument in favor of broadcast regulations that the radio wave medium (the atmosphere/ground) will become "polluted" if people send radio signals at whatever frequency ...
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1answer
403 views

Can Amps be used as a unit of measure for the amplitude of an EM wave?

As far as I know the definition for the amplitude of a wave is the distance between the line $y=0$ and the peak of the wave which in most cases is going to be a unit of length. I also understand that ...
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1answer
42 views

Radio Magneto Tellurics: role of reflection

In the technique of radio magneto tellurics (RMT), plane wave EM radiation incident upon Earth's surface is used to measure subsurface properties. I have read a number of different sources on the ...
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1answer
36 views

When labelling the axis of an AM Signal's frequency spectrum diagram, how can I calculate the frequencies? [closed]

If I have an AM signal with the following carrier and message tones; Carrier: Vc = 120 cos(2π 0.5 x106)t Message: Vm = 40 cos(2π 4 x103)t With a system resistance of 50 Ω, I can calculate the power ...
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1answer
362 views

How feasible is it to track down source of number station radio signals ?

How is it possible and how accurate is it to track down the origin of radio signals used by number stations that emit all around the world (and, as a bonus, how much does it cost approximately) ? I'm ...