Questions tagged [physics]
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19 questions
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Can radio waves travel through metal through high wattage?
"But, radio waves can't travel through metal", I hear you say. Well, you know that, and I know that, so, let's do a experiment. If I use the best antenna (say those parabolic antenna ...
- 805
2
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1
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237
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How to calculate phase constant for a coaxial cable?
inner and outer conductor diameters of 1 mm and 5 mm respectively, is filled
with a non-magnetic PTFE dielectric having εr = 2.55. frequency = 1 GHz.
- 23
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6
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141
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Do changing sidebands have their own sidebands?
An amplitude changing carrier wave causes sidebands to appear next to it when viewed in the frequency domain. But if those sidebands themselves also change with time (because the modulating signal is ...
- 405
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2
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What do radials really do for a vertical antenna?
I have read everything I can find about monopole (vertical antenna) radials, and also watched many YouTube videos that touch on the topic. I see conflicting information about what they do, where a ...
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When a dipole antenna is fed via coax, what powers the ground-side of the dipole?
I've been trying to understand how dipole antennas work, and I believe I understand the basics when they're fed via a balanced feed line. In fact, every dipole physics YouTube video and web page I can ...
- 51
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Can radio waves be made to travel as or along a particle beam? [closed]
Can a laser be used as an antenna?
Can a beam of any type extend transmission distance of an electromagnetic field?
https://medium.com/starts-with-a-bang/this-is-why-the-2018-nobel-prize-in-...
- 1
6
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4
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How far do radio waves travel?
I have read that radio waves just keep traveling but the signal gets weaker because of how the wave spreads. OK, I get this, but what confuses me is that satellites emit signals from space that our ...
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2
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Using approximate signal strength at a distance to estimate reception strength of a radio station
I have some historical data on radio stations, but unfortunately, the dataset only has these variables:
the power of the transmitter, in watts
the coordinates of the radio tower
Unfortunately, I ...
- 185
2
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2
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4k
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How do you calculate the field strength at a given distance?
Given this question from the full license exam in the UK:
What is the field strength at a distance of 7m from an antenna with an effective radiated power of 100W?
in which the answer is:
10 V/m
...
- 1,401
1
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3
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67
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Will removing the metal coating smartphone shell (made of plastic) improve reception/signal strength?
smartphone: Samsung Galaxy S4 mini
coating is probably crome, a few microns thick
could it be that removing the coating will have the opposite effect, as in lowering the signal strength instead of ...
- 11
9
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1
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What's this "crossover" toroid winding called and what is its purpose?
I am winding an EFHW matchbox and many of the designs I've found (including the diagram provided with the kit I bought) include a sort of "twist" when winding them:
(Image taken from this post and ...
- 7,469
5
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1
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Does a low amount of atmospheric noise reliably indicate a lack of propagation?
We know that the primary source of interference at HF is atmospheric noise. Thus, all else being equal, the strength of heard noise is a fair indicator of RX system performance (such as in adjusting ...
- 25k
5
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1
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1k
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Why does the ionosphere reflect some frequencies and not others?
Why is it that some frequencies transmitted at some known direction are reflected back to earth, yet others transmitted at the same direction, power and polarity pass through into space with no ...
- 263
4
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2
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265
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Antenna Design for specific directions
I am designing an antenna for a device and was hoping to gain some insight in the correct design direction for the antenna.
The Idea: A receiver & antenna that fits in a 6" diameter by 3" deep ...
- 241
5
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3
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349
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Energy vs power in transmitters
Higher frequencies have a higher energy, simply stated by Planck's constant. When I am transmitting 100 watts on 500 kHz, and transmitting 100 watts on 5 GHz, is there an energy difference in the wave?...
- 7,660
36
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4
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58k
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Effect of different metals for antenna elements
Other than rust, corrosion, and other reactions with air that would make the use of a metal unfavorable, how do different metals affect the performance?
Let's give Yagi an example:
Let's say I use 4 ...
- 7,660
14
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3
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708
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Why do concurrent FM signals not mix together?
Generally when I hear two conflicting signals they do not mix together, but rather one dominates then the other. This phenomenon can be observed on FM broadcast station when driving out of range from ...
- 1,754
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1
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Why is the speed of light rounded to 286 Mm in calculations involving frequencies below 30MHz?
I understand that in order to make the maths simpler, frequency ($f$) is expressed in megahertz (MHz) and the velocity of propagation in free space ($c$) for frequencies above 30 MHz is expressed as ...
- 1,754
13
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6
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34k
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Calculating Antenna Length on the FCC Exam vs. in Reality
I have seen the following formulas for calculating half and quarter wavelength antennas:
Formula for $\frac{1}{2}$-wavelength antenna (in free space):
\begin{equation}
\mathrm{Length~(feet)} = \frac{...
- 1,754