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15 votes

How far do radio waves travel?

Radio waves don't stop at a distance, they just get weaker; you've read this correctly. The reason that communications stop working at some distance is that the signals are too weak to be understood. ...
Kevin Reid AG6YO's user avatar
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5 votes

Can radio waves travel through metal through high wattage?

"But, radio waves can't travel through metal", I hear you say. Nobody says that. Why would they? Sure, conductive materials attenuate signal, and metals are typically very conductive, but ...
Marcus Müller's user avatar
5 votes

What do radials really do for a vertical antenna?

Both #1 and #2 are the same. Accelerating currents are what sum up to create an EM field. And the law of conservation of charge requires that the currents be balanced. If you have a quarter wave ...
hotpaw2's user avatar
  • 13.5k
5 votes
Accepted

How do you calculate the field strength at a given distance?

The field strength in volts/meter as a function of effective radiated power and distance is given by: $$E=\frac{7.01\sqrt{P_{ERP}}}{d} \tag 1$$ where d is the distance from the radiating antenna in ...
Glenn W9IQ's user avatar
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4 votes

Will removing the metal coating smartphone shell (made of plastic) improve reception/signal strength?

Telephones are designed as a system. So, yes, the plastic case, including a potential coating, have been incorporated in tests, and in consequent optimization (at least for large-scale mid- to high-...
Marcus Müller's user avatar
4 votes

Effect of different metals for antenna elements

If you are interested in space communications (EME and satellites) even small losses are important since losses have room temperature. The sky as well as a good preamp should be well below 100K while ...
sm5bsz's user avatar
  • 1,009
4 votes
Accepted

How to calculate phase constant for a coaxial cable?

The velocity of propagation for the TEM mode $V_p = \frac{c}{\sqrt{\epsilon_r}}$, i.e. in your case about $0.626\,c$, or $1.877 \times 10^8\,\frac{\mathrm{m}}{\mathrm{s}}$. (This is a bit different ...
hobbs - KC2G's user avatar
  • 12.5k
3 votes

Calculating Antenna Length on the FCC Exam vs. in Reality

Thanks for the posting everyone! For licence test I took this approach after reading everyone's post & searching though all the technical details you posted. Convert Frequency to wavelength in ...
Mark Van Skiver's user avatar
3 votes

Using approximate signal strength at a distance to estimate reception strength of a radio station

The methodology needed to accurately calculate the radiated r-f power needed to generate a given field intensity at some distance along a terrestrial path is highly complex — probably beyond the ...
Richard Fry's user avatar
  • 2,922
3 votes
Accepted

Using approximate signal strength at a distance to estimate reception strength of a radio station

We have some clues from a historical perspective. In the January 1917 edition of The Radio Experimentor, author H. Winfield Secor noted that approximately 50 kW (kilo-watts) of transmitter power was ...
Glenn W9IQ's user avatar
  • 18.6k
3 votes

When a dipole antenna is fed via coax, what powers the ground-side of the dipole?

But how do they work with an unbalanced feed line, such as coax? In that case, the shield of the coax is connected to one half of the dipole. What's driving that half of the dipole? The current in ...
Kevin Reid AG6YO's user avatar
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3 votes
Accepted

Can radio waves be made to travel as or along a particle beam?

Light waves and RF waves are both electromagnetic radiation. The only difference is that we can see the narrow band of frequencies that we call light. There is a common misconception that laser ...
Glenn W9IQ's user avatar
  • 18.6k
3 votes

How far do radio waves travel?

The curvature of the Earth also makes a difference between how a signal will propagate near the ground versus in outer space. And at a large enough distance, the random quantum behavior of the atoms ...
hotpaw2's user avatar
  • 13.5k
3 votes

What do radials really do for a vertical antenna?

Radials do both, but reflect is the wrong word and the reasoning behind increasing conductivity misses the point. A monopole vertical antenna is really still a dipole, except that the vertical portion ...
user10489's user avatar
  • 6,485
2 votes

When a dipole antenna is fed via coax, what powers the ground-side of the dipole?

Good question! Properly operating, the coax shield is at ground potential. But a dipole needs both sides driven, ideally with voltages symmetrical around ground potential. So how can this work? The ...
Phil Frost - W8II's user avatar
2 votes

When a dipole antenna is fed via coax, what powers the ground-side of the dipole?

There is no "ground side" of an antenna or feed line at radio frequencies. A wire of any dimension longer than a fraction of a wavelength in an RF field can have very different voltages at ...
hotpaw2's user avatar
  • 13.5k
2 votes

Will removing the metal coating smartphone shell (made of plastic) improve reception/signal strength?

I once removed the cover of an HTC One X for cleaning purposes. As curious as I am, I switched it on and noticed really poor reception. Upon further investigation, I concluded that some metal parts ...
Daniel Hofer's user avatar
2 votes

Do changing sidebands have their own sidebands?

Part of your problem is in thinking that "a changing carrier causes sidebands to appear next to it" is a physical cause and effect. The carrier doesn't create the sidebands, the sidebands ...
hobbs - KC2G's user avatar
  • 12.5k
1 vote

Do changing sidebands have their own sidebands?

There are two sidebands: Upper sideband and Lower sideband. You don't get an upper upper sideband. :) The carrier is merely the center frequency, and is not part of the audio modulation or the ...
user10489's user avatar
  • 6,485
1 vote

Do changing sidebands have their own sidebands?

For a linear modulator the frequency spectrum of the baseband modulating signal is replicated just once into each sideband. It doesn't keep being copied. So each sideband will have the same bandwidth ...
Graham G8URP's user avatar
1 vote

Do changing sidebands have their own sidebands?

The sidebands are just the audio frequency signal moved up to the RF carrier frequency. If you turn the soundwaves into an electrical signal and do the Fourier transform of that signal you will two ...
QuantumMechanic's user avatar
1 vote

Do changing sidebands have their own sidebands?

The r-f spectrum of a double-sideband "AM" transmitter includes the carrier wave and the upper and lower sidebands produced by the modulation of that transmitter. It is being assumed in this ...
Richard Fry's user avatar
  • 2,922
1 vote

How do you calculate the field strength at a given distance?

How do you calculate it? In the general case, you use a numerical EM field solver. Without a specification of the antenna geometry and exactly which point 7 meters away is under consideration, this ...
Phil Frost - W8II's user avatar
1 vote

Calculating Antenna Length on the FCC Exam vs. in Reality

Need to get a few things out of the way to understand why some things are. Velocity Factor - speed of a electromagnetic (EM) wave through ANY material. Frequency - Speed in Hz of a (EM) wave. 20Hz to ...
Dennis N7TZQ's user avatar
1 vote

Calculating Antenna Length on the FCC Exam vs. in Reality

I always use the 468 formula and have for the past 30 years and ALWAYS had a perfect SWR and matched antenna. I have made over 200 dipoles and I have NEVER had to trim to get a perfect antenna. I also ...
Mark Warren's user avatar

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