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0answers
13 views

Directivity of dipole antennas inconsistency

I'm trying to model the directivity of dipole antennas of differing lengths. There are two main ways I've thought to approach this. The predicted radiation pattern is given by ...
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1answer
27 views

Recommended reading about antennas? [on hold]

I am trying to learn a bit about antenna theory in order to understand how Nikola Tesla may have misunderstood them. (Thank you CuriousOne for your response to my earlier question! It was helpful in ...
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0answers
48 views

Why is the satellite dish still needed?

How much does it amplify the signal? The receiver cannot pick up the signal without the dish? Is it possible that it will disappear in 10 years? As the sensitivity of the receiver is enhanced? ...
-1
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0answers
24 views

Polarization important in radio [closed]

Why is polarization important in radio? Which signals are affected least by it? for the 1st part of the question i find it: "An antenna is a transducer that converts radio frequency ...
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0answers
87 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 ...
0
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1answer
22 views

Why should we extend the radio antenna to make it work though we board on enough height? [closed]

The old FM radios have an antenna to receive radio frequencies and work on them. If I am in ground floor, I have to extend or spread the antenna to make the radio work. Now if I go to the first or ...
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2answers
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 ...
0
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0answers
21 views

How much energy would be required to remotely induce a signal in a wired network (e.g. Ethernet)?

How much energy would be required to remotely induce a signal in a wired network, such as Ethernet? Assume, for the sake of discussion, that the wired network has a single cable of length $l$ (eg 10 ...
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0answers
29 views

Half wave antenna

I need to calculate the magnetic field intensity at a distance $x$ and angle $\theta$ for a half wave dipole antenna. I know the length of the antenna is $$ l = 333.33mm$$ and the magnetic field ...
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0answers
37 views

Calculating instantaneous field strength for known signal source

I was referred here from electronics stackexchange. Suppose I have a time varying signal source V = Vm cos(wt). This source is fed to a half wave dipole antenna which in turn radiates electromagnetic ...
1
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1answer
59 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 ...
1
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1answer
87 views

Light is/produces a electromagnetic wave, but is the opposite also true?

A similar question has been asked, and to some extent the answer is: you need an antenna with $L \approx 200nm$. But it's not entirely clear to me if this is completely hypothetical, as "Marek" also ...
3
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2answers
147 views

How do radio antennas follow electrical rules

Power = current times voltage. However current requires a complete circuit to 'flow'. How can a 1,000 Watt antenna work if the output of the transmitter is connected to a single emitting wire or ...
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2answers
69 views

Will radio waves bend to reach receiver?

I was wondering if receivers just catch the radio waves that pass through, or if they actually attract the waves like a magnet. In other words, will a radio wave moving in a straight line bend in ...
1
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0answers
27 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 ...
0
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2answers
103 views

How exactly do radio waves work?

So I understand that a radio wave is created by electrons oscillating in the antenna. But how does this create a radio wave? How are the electric and magnetic field "emitted" by the electrons? If you ...
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3answers
108 views

How does the tuner really work in a crystal set?

I would like to know how and why the tuner works in a crystal set radio. I already know all the theory and the "formal definitions" (this creates a resonant circuit which responds to an alternating ...
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0answers
20 views

Radio wave propagation path loss coefficient below 2?

We did a series of measurements of radio wave signal strength. The setup was between stations on top of flat roofs of neighbouring houses (with line of sight). We are interested in the path loss ...
1
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1answer
68 views

Dipole antenna $E$-field direction

I was looking up dipole antennas on Wikipedia, among other sites. I came across this animation: and was wondering why there wasn't any field lines in perfectly vertical direction. In the case of a ...
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2answers
53 views

Do a receiving antenna interfers with an emitting antenna?

As I understand: Accelerating electrons generate electromagnetic waves. An emitting antenna have an alternating current (electrons are moving) which generates an electromagnetic waves. The ...
1
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0answers
69 views

How is my guitar cable picking up clear radio-signals?

I've recently noticed radio-signals coming through my guitar amplifier. I'm on the top floor of a building in a densely populated city, with a clear visual path to many other buildings. My guitar ...
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0answers
31 views

If we had a radio antenna produce visible light? [duplicate]

If we had a radio antenna produce visible light would it degrade the quality of the antenna due to the light production. How fast would be the degradation?
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0answers
10 views

Getting H-Plane Cut from Near to Far Field Transformation

I am using the Near to Far Field Transformation method described in http://www.keysight.com/owc_discussions/servlet/JiveServlet/download/72-15457-47956-2405/36-tkadlec_roman.pdf. The method describes ...
0
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1answer
37 views

Connecting two antennas to provide signal

Problem: I am in a room without FM signal. I would like to provide FM signal to the room. If you have a hole for coaxial cable, which can connect a place with signal and the room, is it possible to ...
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2answers
75 views

There is no reverse flow of energy in a mismatched transmission line, is this correct?

I have already posted this question on the Amateur Radio site, but I would value opinions from a more theoretically based group. Is this text correct? I use it when helping people to study for ...
2
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0answers
29 views

How to mathematically model a realistic aperture illumination?

I want to know a mathematical expression that I can use to model a realistic aperture illumination to produce the primary beam of an antenna so that the radial distribution of this aperture ...
0
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2answers
67 views

Is a longer antanna better for reception ? Or just more directional?

Let's say I have two antennas, A1 and A2, and they have identical radiation profiles. So the relative radiated energy in a given direction is the same for both antennas. Let's assume also that we ...
0
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1answer
90 views

If electromagnetic waves can be generated by oscillation of a coil why can't light? [duplicate]

I was recently reading how electromagnetic waves are generated using oscillation of a current in an antenna. Why is it that this principle cannot be used to generate light?
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2answers
148 views

Rigourous Treatment of Antenna Theory/Physics

As a rising senior who has finished his QM sequence but not yet done an E&M/optics sequence, but is about to start a research project that will be a large part antenna design and optimization, ...
8
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1answer
189 views

Why do I hear voices when I touch my turntable needle?

So I was trying to figure out the reason why my old (and probably sufficiently damaged) needle on my phonograph (turntable) was not working like it was a little while ago. With my headphones on, I ...
0
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1answer
35 views

Wideband metamaterials in mobile-telecommunications bands

Were there any metamaterials (materials, settings, geometry) studied that are non-resonant (not frequency selective) in the frequencies between 700 MHz and 2700 MHz, therefore useful for mobile ...
1
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1answer
35 views

Layer of graphene on reflector of an antenna

First of all I have no idea how well graphene "sticks" to other metals, but let's suppose it does (well, if I may please ask you to reply to the "stick" question too...). Given the material great ...
1
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0answers
57 views

Why are most antennas in cellular networks +/- 45° polarized?

I've just been asked a strange question that I cannot find an answer to (even on the internet it seems I can't find any explanation for this) and I ended up wondering why most of the antennas which ...
1
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0answers
36 views

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 ...
0
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1answer
53 views

$H$ field from corresponding $E$ field (antenna)

The $E$ field at $kr >> 1$ due to a short dipole oriented in the $z$-direction and located at the origin is: $$E_0 = \frac{10^3e^{-jkr}}{r}\sin\theta\space\space(V/m)$$ Can I just solve for the ...
0
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0answers
64 views

Finding skip distance/one-hop distance for a radio wave?

I've been racking my brains all afternoon trying to figure this out. Here's the question we're given: At an altitude of 400km is the reflective layer in the atmosphere. What is the maximum distance ...
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0answers
99 views

What have we built? A resonant loop antenna? Rhombic?

Some background, my partner and I have built an antenna we are supposed to characterize for an assignment, and compare it to physical predictions. However, we don't know what type of antenna we have ...
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2answers
104 views

Explanation for: A monopole antenna must contain a resistor (or equivalent) and therefore must have 2 terminals?

Could someone explain why this sentence makes sense: A monopole antenna transfers energy from electrical domain to the electromagnetic domain, hence must contain (equivalently) a resistor, hence ...
0
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1answer
88 views

Proof the directivity antenna formula in degrees

For a single-lobed pattern the beam solid angle is approximately given by $$\Omega_A \approx HP_E.HP_H$$ where $HP_E$ and $HP_H$ are the half-power beamwidths in radians of the main beam in the E ...
0
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1answer
62 views

Effective Area of Isotropic Antenna: Explanation?

I'm reading some introduction to antenna theory and I've often puzzled on the equation: $$ A_{eff} = \frac{\lambda^2}{4\pi} $$ which relates the effective area by which an antenna captures radiation ...
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0answers
30 views

Effective aperture of an isotropic antenna; question on polarisation

In this answer to Effective aperture of isotropic antenna, a factor of 1/2 was included to account for polarisation, but the antenna was isotropic. How can this discriminate polarisation?
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1answer
355 views

Current distribution on a dipole antenna

It is known that the current distribution on a thin dipole antenna is always sinusoidal: http://www.antenna-theory.com/antennas/dipole.php How can I prove this?
6
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2answers
556 views

Why doesn't my mobile phone pick up the electro-magnetic wave emitted by my water heater?

I admit my knowledge of physics is very little, but I did study topics on EM and stuff in school. I was reading about computer networks and I read about antennas and how they are just wires or strips ...
2
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1answer
47 views

Does array gain violate the laws of physics or not?

I am a bit disturbed lately since I don't know the answer this basic problem. Say we have a standard isotropic antenna with some fixed parameters (load impedance, etc), and we feed this antenna with ...
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3answers
1k views

Detectability of interstellar messages

Recently a debate started whether it is a good idea to send more messages into space in the hope of having alien civilizations receive them. There are some predecessors, most notably the 1974 Arecibo ...
2
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0answers
108 views

Phased non linear array antenna - First Sidelobe

I have a problem I cannot seem to solve and I REALLY need some help. It's about phased-array antennas whose dipoles are not equally spaced, not equally phased, not equally fed (amplitude). Let's ...
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0answers
148 views

How is it that 62" is the best length for 72Mhz receiver?

According the this article (which was published somewhere in 2005-2008 I think, but it's still comes up first in Google) the best length for a 72Mhz receiver antenna is 62" (~157.5cm). This puzzles me ...
2
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4answers
902 views

How do radio waves reach receivers without being canceled out by interference?

When I think of waves traveling through a medium, I tend to think of the double slit experiment or waves in a pond. In those cases, waves are canceled out by destructive or constructive ...
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2answers
69 views

Does the power weakening of an electromagnetic transmission over distance depends on the beam's width?

Does the power weakening of an electromagnetic transmission over distance depends on the beam's width? If I emit an omnidirectional electromagnetic transmission, its power weakens in the ratio of ...
0
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1answer
51 views

Power spectral density of noise: what is $\mathcal{N_0}$ in $S_X(f)=\mathcal{N_0}/2$?

My question is regarding power spectral density of white gaussian noise. It is known that the power spectral density of white gaussian noise is $$S_X(f)= \frac{\mathcal{N_0}}{2}$$ My question is does ...