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11
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3answers
653 views

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 ...
9
votes
2answers
1k views

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 ...
8
votes
1answer
294 views

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 ...
8
votes
1answer
114 views

Where can I find information for how to create amateur radio telescope?

Where can I find good source of information for how to create amateur radio telescope. Particularly interested in creating Fresnel Zone Plate Antennas (aka flat dish). design, diagrams, ...
7
votes
1answer
4k views

How does a digital radio tuner work?

I believe I understand how tuning a radio with an analog tuner works: turning the dial physically changes the length of the antenna, which determines which broadcast wavelength will resonate in the ...
7
votes
3answers
1k views

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 ...
7
votes
2answers
177 views

Does a radio receiver add a load to the transmitter?

If I have a dynamo connected to a switch and a load (such as a light bulb), the load on the dynamo is increased when the switch is closed and the light comes on. The dynamo gets harder to turn. Is ...
6
votes
2answers
197 views

Multiple channels of information in single electromagnetic wave?

I'm trying to understand how can multiple radio stations transmit information just by transmitting using different frequency. The way I understand it all those different frequency waves add up to a ...
6
votes
3answers
219 views

Can visible light be emitted from a non-thermal source?

I was reading about thermal and non-thermal radiation and I was wondering if visible light can be emitted from a non-thermal source?
6
votes
1answer
3k views

Adverse Health Effects of Strong Radio Waves

A while ago, I was hiking near the Hollywood Sign in Los Angeles. When I got to the sign, I found out it was fenced off; with several signs and a security camera promising prompt enforcement. As I was ...
6
votes
2answers
175 views

References for Radio Imaging?

I'm really intrigued by a bunch of questions like 'what do radio waves look like?' 'how much RF radiation is there in the town I live in?' 'how specifically does RF imaging work?' But I think I need ...
5
votes
4answers
2k views

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 ...
4
votes
4answers
4k views

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 ...
4
votes
1answer
267 views

Why is it that when driving in a car, and a lightning bolt strikes, my AM radio gets cut off for a while, but FM stays on?

I noticed this one day, a lightning/thunder occurred and my Fabulosa Spanish music died for a second. But not FM?
4
votes
2answers
469 views

What happens to the energy not absorbed by a radio?

If a radio tunes to a specific frequency, where does the excess energy go? If one continues to hit the resonant frequency, shouldn't the wire begin to melt at some point from too much energy?
4
votes
2answers
481 views

Radio communication and antennas

I'm trying to understand how an antenna is able to understand, but have a few quesions: I understand that for an antenna to distinguish between 2 (or more) signals, they have to be in different ...
4
votes
2answers
84 views

How does a fixed amount of transmitted radio energy supply an unknown number of destinations?

I did some maths and physics up to the age of 18, and hold an amateur radio licence. This thing has puzzled me for a while - does reception of an electromagnetic wave imply an interaction with the ...
4
votes
1answer
101 views

AM Receiver and sideband frequencies

How sorry for "dummy" question. I have difficulty to understand how the AM receiver. Being a child I was taught that AM receiver resonates only with the radio frequencies it is tuned to, and "passes" ...
4
votes
1answer
45 views

Missing radio source coordinates in G/T measurement technique ITU-R S.733.2

Section 3 ‘Suitable radio stars’ of this recommendation lists the different stars/nebula and their corresponding flux-densities that can be used in the G/T measurement. There is no reference to the ...
4
votes
4answers
2k views

How does radio receives signal from particular station?

When you tune your radio (digital or analog) to receive say 100 MHz frequency and while in the environment there are hundreds of channels everywhere around the radio. How does it chooses to receive ...
4
votes
0answers
141 views

How is extremely low frequency (ELF) radiation collected by a submarine antenna?

The U.S. Navy Project ELF managed to generate extremely low frequency (ELF) radiation at down to $\approx 76$ Hz (implying a wavelength of $\approx 3,945$ km!). I was curious, what kind of receiving ...
3
votes
2answers
378 views

Why is bandwidth, range of frequencies, important when sending wave signals, such as in radio?

So in wired/wireless networking and radio, signals are sent in form of wave. Then the concept of bandwidth comes in, which is the difference between highest frequency and lowest frequency in a signal. ...
3
votes
2answers
148 views

What does an analog voice transmission look like in the visible spectrum?

Analog radio signals are transmitted using light in the radio area of the spectrum. If it was transmitted using the visible spectrum instead (using a visible light emitting device instead of a radio ...
3
votes
2answers
113 views

How are electromagnetic waves differentiated?

I would like to know how the signals for remote controlled cars, radios, etc.. That use radio waves are told apart from each other. I know that the radio waves are modulated to encode data and the ...
3
votes
3answers
6k views

Penetration versus Frequency

I would like to know the relation between penetrating ability and the frequency of a wave. For example, gamma waves have high frequency and high penetrating power: intuitively I imagined this as ...
3
votes
1answer
234 views

Radio vs optical telescope imaging

As I understand, the visible light from an optical telescope is focused on a sensor which correlates light exposure to an electrical voltage, which is then converted to an image. A single antenna ...
2
votes
5answers
112 views

If an antenna must be $\frac{1}{4}$ of the wavelength, how can car antennas be so small?

If the transmission antenna has to be $\frac{1}{4}$ of the wavelength, how can the car antennas' size be much less than that and properly receive the radio signal?
2
votes
3answers
3k views

Is visible light and radio waves made of the same thing?

I understand that there is such a thing as the electro magnetic spectrum, and that light and RF are both on it, so dose that mean that they are made of the same thing? Just at different frequencies.
2
votes
1answer
384 views

Where are the harmonics in the radio spectrum?

When I strike a string on my guitar and look at the audio spectrum, I can see the fundamental frequency as a large peak. I can also see the harmonic frequencies as a train of little peaks at ...
2
votes
2answers
174 views

Frequency Modulation

If FM radios work by modulating the frequency, how is it that we can tune into a specific channel, and hear a song or station? Wouldn't the channel need to be modulated along with the varying ...
2
votes
2answers
754 views

How does repeater amplify the radio signals?

When you send some kind of radio signals at some frequency say 5 GHz to a repeater and it transmits it back at higher power, what change is made to the radio signal? For example: Will it be ...
2
votes
2answers
143 views

Radio Transmission distance (FM) [duplicate]

I am trying to find a formula (if one exists, and this is the right place) to try and calculate how far a radio station can transmit, under ideal conditions. I have searched Google, and I can not find ...
2
votes
1answer
177 views

What is the diameter of the sun as a function of wavelength/frequency (around 10GHz)?

I have this vague recollection of being told that the diameter of the apparent surface of the sun is a function of what band you observe it in. I'm looking for a model of this that works for bands in ...
2
votes
1answer
792 views

Determining a radio signal's range

If I know the: Frequency Effective Radiated Power Height Above Average Terrain Radiation Center Above Mean Sea Level Radiation Center Above Ground Level of a radio signal / tower, is there a way ...
2
votes
1answer
219 views

Radio waves and frequency of photon

Is 89MHZ station emitting photons of 89MHZ frequency? (I mean $\nu$ in $E=h\nu$).
2
votes
1answer
89 views

How does rust behave as a PN junction?

Reading about old-fangled radios the reference quoted below indicates it was/is possible to use a rusted razor (or perhaps any similar thin corroded metal strip) as a detector. Some resourceful GIs ...
2
votes
5answers
754 views

Radio waves within an atom

What effect does the quantum world have on radio waves? For example, if I could shrink myself down and stand on the nucleus (or even smaller sub atomic particles making up the nucleus) with a device ...
2
votes
1answer
48 views

Import of Celestial Effects on Satellite Radio Interference

Some internet (among other) infrastructure comprises satellites, which beam communications in radio frequencies. These satellites, to ground observers, appear as very small solid angles in the sky. ...
1
vote
4answers
677 views

Radio antenna producing waves in the visible spectrum

If a radio could produce waves in the visible light spectrum, what would the result be? This is a thought experiment that I've pondered for a few years now. I realize there are a few/many real-world ...
1
vote
1answer
908 views

How radio waves penetrate through buildings?

For example how radio signals of a base transceiver station (BTS) penetrate through buildings?
1
vote
3answers
159 views

Are communications between computers faster by electrical signals via copper cables or electromagnetic signals?

Assume that there are two computers which are connected with a copper cable, e.g. Ethernet. Also, there is a radio connection between them, e.g. AM radio, in order to exchange data. When we try to ...
1
vote
1answer
53 views

Can extraterrestials detect our messages?

We transmitted several messages to the space and listening to space for signs of intelligent life for years (SETI). Assuming they have at least the same technology we have, could they detect these ...
1
vote
2answers
480 views

Is data which rides on the carrier frequency dangerous?

My understanding of broadcasting data via electromagnetic radition is, that the data "rides" on a carrier frequency on which it is radiated. I am aware of the fact, that those carrier frequencies are ...
1
vote
3answers
88 views

Plane waves - EM wave

An accelerating electric charge will emit transverse electromagnetic waves. These waves are propagating away in wave fronts that become flatter and flatter as getting further from the source. So they ...
1
vote
1answer
96 views

AM vs FM radio under bridges

I know what the difference between AM (Amplitude Modulation) and FM (Frequency Modulation) radios is. However, I noticed that when I drive under a bridge while listening to a station on AM, it just ...
1
vote
3answers
168 views

Is it possible to produce gamma radiaton using radio emitter?

As in the title, I'm wondering is it possible. I think it is possible, because we have powerful enough radiotechniques and gamma radiation are just EM waves, not particles. However I think is ...
1
vote
2answers
747 views

What makes radio waves refract?

What materials cause radio waves to refract? What are the radio IOR's of these materials?
1
vote
1answer
102 views

Getting a given wavelength radio signal given an antenna with real-world constraints

Supposing you are given a transmitting antenna of whatever type of metal is most commonly used these days, and supposing that you are applying an AC current with the intent of transmitting a 1 m ...
1
vote
2answers
389 views

Working of a crystal radio

I have been reading about how a crystal radio works and I have one question below: It says, the energy in form electric current from a specific frequency will be stored in the coil (or a resonator) ...
1
vote
1answer
227 views

Cellphone RF radiation

First, what determines the strength of an RF signal? Why is it said that a cellphones radiates more energy when the reception from signal tower is lower in strength. Why is it said that RF gets ...