# Tagged Questions

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38 views

### Gravitational waves vs. electromagnetic for telecommunications

Assuming it would be possible, what would be the advantages/disadvantages of manipulating gravitational waves for telecommunications versus using electromagnetic?
40 views

### What is absorption rate of WiFi and Bluetooth RF in water? [on hold]

Specifically, frequencies 5.75GHz and 2.4-2.485GHz. I want to place a hermetically sealed circuit at the bottom of a gold fish bowl, and want to know if the water will significantly attenuate WiFi or ...
52 views

### How long does it take for an Astronaut around the Moon to receive a spoken message from Houston? [closed]

How long does it need till an Astronaut gets a spoken message from Houston and then replies to it? What happens if there is an emergency situation where a solution has to be suggested within a time ...
43 views

### Why LiFi can't penetrate like WiFi? [closed]

My common sense says that Lifi signals can't penetrate through walls (since visible light cannot) but other part of the electromagnetic spectrum can, I mean radio signals which power WiFi. So is ...
27 views

### Why do Very high frequency (VHF) radio waves have limited range?

Why do ultra high frequency radio waves (ex: 2.4GHz or 5GHz) have limited range ?Is it to do with absorption ?If so how do these waves get absorbed when the ELF waves are not ,and on the other side ...
25 views

### Transmission line model proof?

Why 2 distributed lines is represented with series inductor and resistor along with parallel capacitor and resistor? What is the motivation for that? In circuit theory I Knew the assumptions to ...
73 views

### How do signals go through solid objects? [closed]

So many types of signals pass, or seem to pass I don't know, through solid objects. How do they do this?
56 views

### Fresnel zone with different antenna heights

I've looked at the formula to calculate the first Fresnel Zone: $$r=17.31 * \sqrt{\frac{d_1*d_2}{f*d}}$$ whereby $d_1$ and $d_2$ are distances from the obstacle to the link end points in meters, $r$ ...
5k views

### How to imagine WiFi signal propagation?

When thinking about how the WiFi signal propagates through a household, can I use the following thought experiment? Assume absolute darkness. Place a strong lightbulb where the WiFi access point ...
94 views

### Why is it that fractal antennas can filter out so many frequencies?

As known, fractal antennas are used for example in cell phones. But why is it that so many different kinds of frequencies can be filtered out of the forest of radio waves surrounding us? Is it because ...
2k views

### How do you make a spherical radio wave?

A vertical rod, a usual dipole, produces radio waves in the horizontal plane, mostly in two opposite directions: If that is possible, how do you produce a spherical EM radiation? should the ...
43 views

### Can video data can be transmitted via radio frequency? [closed]

My friend says that it's possible to transmit an video by converting it's data to radio frequency?
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### Colpitts oscillator

why colpitts oscillator is used for fixed radio frequency?I think they are used because it produces frequencies in the radio spectrum am I correct
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### Length of a transmission line for a known Zin, Z0 and Zload

From the transmission line equations i have the following impedance transformations equation: $$\ Z_{in} = Z_0 \frac{Z_{load}cosh(\gamma) + Z_0sinh(\gamma)}{Z_{load}sinh(\gamma)+Z_0cosh(\gamma)}$$ ...
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### Why are magnetron apertures in home microwaves so small?

I'm curious why magnetrons from a home microwave like in the image below can have an aperture between the magnetron cavity and the waveguide that is significantly smaller (2-6mm usually) than the ...
71 views

### Why doesn't a transmission line mess up an antenna resonance?

I don't understand why the resonance of an antenna is not affected by the transmission line to the receiver. For example, given a dipole antenna like the following: The antenna length is carefully ...
207 views

### Why is UHF so much more popular than other frequencies for radio? [closed]

Great most of popular radio stations nowadays operate in UHF frequencies. I know this was not the case in the past, long, medium and short wave radios much more popular (and AM encoding being quite ...
18 views

### Can electroluminescence be theoretically used for RF communication?

I know that photon energy of radio frequency, 3 kHz (1.24e-11 eV) to 3GHz (1.24e-3 eV), is much smaller than the thermal energy $k_B T$ at 300K (25.8e-3 eV), which in turn is much smaller than typical ...
84 views

### Can we determine the location of a radio station if we know the wavelength and frequency of radio wave emitted by that radio station?

let say that we can detect the wavelength and frequency of radio wave then can we detect that from where these radio waves are coming or from how much distance these waves are coming?
28 views

### Is it possible to make an antenna that's more compact than a split-ring resonator antenna? [closed]

I'm aware that a split-ring resonator antenna works efficiently by being half the size of a classic antenna. But is there any design that takes even less space? I have in mind millimeter or micrometer ...
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### Why is the modulating shape appear in both sides of the carrier signal in AM?

It's about Amplitude Modulation. Can anyone tell me why is this signal wave or modulating waveform shape appears in both sides of the carrier sine wave? Why not in one side only? x_c(t) = A_c[1 + \...
34 views

### Low frequency video transmission

Can a video signal be transmitted for a short distance ($30\,\mathrm{cm}$) by a very low frequency carrier ? Here my concern is about frequencies $1\,\mathrm{hz} - 100 \,\mathrm{hz}$ . Transmission ...
36 views

### Wavelength, frequency, and radars [closed]

I'm doing a high school paper on the effects of frequency alterations on a radar image. Can someone recommend a book which I can use?
52 views

### Why do radio stations have ranges

If you have been on a long car ride you would know that the signal of a radio station becomes weaker and weaker and then stops. But since radio waves are just a wavelength of the electromagnetic ...
19 views

### Injection current modulation with a modulated RF signal to drive laser

I am using an RF modulated injection current to drive my laser in such a way that the modulation index = 0.8. At this point, I see the carrier and first sideband on the spectrum analyzer. If I now ...
13 views

### How do i calculate the “attenuation effect” that of a perforated aluminum sheet?

I am conducting an experiment test different configuration of perforated aluminum sheets. I am working with radio waves but i am having am hard time finding any equations or properties for this ...
80 views

### RF disturbances produced by transmission power lines

I need a book or paper that contains "the effects of transmission lines on the radio frequency transmission and disturbances". Could you help me find a useful textbook? Thank you
506 views

### materials that can render Bluetooth useless

i'm currently preparing some experiments about using Bluetooth in real life. And to make the data more vary, i need some materials that can really giving side effects to Bluetooth functionality. i've ...
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### How to describe frequency spectrum with samples?

I posted this same question in math, but nobody is answering, so I thought I'd give a try here too... To me the question is pretty straightforward, but nevertheless I have to explain its background ...
125 views

### How do NFC/RFID devices transmit data?

I am designing an NFC device but am still a little unsure about the principles behind NFC/RFID. From what I understand: A primary coil constantly emits a 'carrier frequency' magnetic field. This ...
95 views

### Light / TEM wave in a hollow waveguide

I'm cramming for my EMF exam, and a question came up: Light in free space is an example for a TEM wave, isn't it? (Maybe thats already my mistake) And we learned that in a hollow waveguide only TE ...
213 views

### Cantenna and waveguide

I'm studying for a lecture of RF and wave guides and i'm currently building a cantenna. I have two questions about it construction and on how it works. My questions are about the lengths of the ...
136 views

### Do neutron stars produce sound?

I've watched a video on youtube about neutron stars as called (pulsar) and it claims that pulsars produce this sound. then i found that they produce radio waves which can be converted to sound. Radio ...
251 views

### Do Sidebands mean the frequency of an AM radio wave is not constant?

I'm studying for A-level now..... I have read some other posts explaining how the sidebands generated after the carrier wave is modulated. So, if there is sideband frequency, the frequency isn't ...
68 views

### Building a Crystal Radio Questions

I have been reading several books and articles about building a crystal radio and the explanations about the inner workings of the circuit seem vague. All articles and books mention the coil and the ...
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### Discernible “frequencies” of magnetic fields that do not affect each other

Two magnets secured to a surface close to each other in a fashion such that their constant attraction to one another is counteracted by the normal force of the securement of each. Is there a way to ...
224 views

### Why does a non-contact voltage detector light up when you touch a plasma ball with the other hand?

I am doing a science experiment and we decided to try holding a non-contact voltage detector up to plasma ball. We were surprised that it would light up when it was 3 ft away from the plasma ball. I ...
25 views

### Transmitting to and from low earth orbit?

I'm a hobbyist and I'm currently thinking about building a Cubesat. I'm currently designing PCBs, casing, etc. I was wondering what variables are involved with sending data to and from 250km - 350km ...
175 views

### Does rain jam radio signal?

I have experienced several times that heavy rain seems to jam the signal a radio of a bus receives. The only explanation I have is that the rain drops also become weak emitters, if a radio wave hits ...
33 views

### Ground influence on 434 MHz radio signal

I have read in a paper that ground acts as reflector for radio signals in 434 MHz band. Why is that the case?
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### How is spectrum controlled? [closed]

I understand that spectrum is considered a national resource for many governments. It is akin to land, water and other resources. It is also a scarce resource. I wonder how is it that government ...
155 views

### polarization of a transverse wave travelling in ionosphere with polarization direction perpendicular to earths magnetic field

Assume a transverse electromagnetic wave entering ionosphere such that its Electric field of wave is perpendicular to earths magnetic field. Now, i read that as it will enter plasma, the wave will ...
88 views

### Chaff-RF Relationship?

What is the relationship between chaff length and the frequency it is meant to interfere with? I've read that specific lengths of chaff are more effective as a countermeasure for specific frequencies,...
241 views

### Radio wave propagation in ionosphere

Radio communication is based on the concept that a radio signal incident on the ionosphere is reflected if the frequency of the wave matches the plasma frequency. But what exactly happens? Is it ...
77 views

### The influence of the antenna height

I am working on a model of a transmitter. The transmitter is attached to the wheel of the vehicle and thus constantly changes it's height. In other words capacitance between antenna and ground is ...
36 views

What happens if someone would make a wire coil around nuclear reactor core? What are the possibility to capture radioactivity directly?
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### Why can microwave (in microwave oven) heat the food but wifi can't? [duplicate]

As far as i know, microwave (used in microwave oven) and wifi all operate on the same frequency, but why microwave can heat the foods while wifi wave can't?