How does a Radio Antenna Work?

  • Context: Undergrad 
  • Thread starter Thread starter darrink1
  • Start date Start date
  • Tags Tags
    Antenna Radio Work
Click For Summary

Discussion Overview

The discussion centers on the functioning of radio antennas, exploring both transmission and reception mechanisms. Participants examine the physical principles behind antenna operation, including electron behavior, efficiency, and resonance, as well as the differences between transmitting and receiving antennas.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant describes the generation of an AC signal on a conductor and the oscillation of free electrons, suggesting that this oscillation leads to the release of photons, contingent on the antenna's length being sufficient to accommodate at least 1/4 wavelength.
  • Another participant counters that photons are emitted whenever electrons oscillate, regardless of antenna length, emphasizing that efficiency in converting electrical power to electromagnetic radiation varies with antenna design.
  • There is a query about the nature of "efficiency," specifically whether it pertains to the quantity of photons emitted or their directional usability for receivers.
  • One participant explains that radio-frequency radiation is typically modeled as waves rather than discrete particles, noting that efficient antennas produce larger amplitude EM waves with minimal heat loss, while inefficient ones convert more power into heat.
  • A detailed explanation is provided regarding radiation efficiency, input impedance, and resonance in antennas, highlighting the differences between half-wave dipole and quarter-wave monopole antennas.
  • Another participant raises a question about the factors determining the frequency of light emitted by materials after photon absorption, indicating a curiosity about the underlying material properties.
  • The discussion also touches on the reception process, where induced currents on the antenna generate a voltage that propagates to the receiver, with mention of techniques like Automatic Gain Control (AGC) to manage signal amplitude variations.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between antenna length and photon emission, as well as the concept of efficiency in antenna design. The discussion remains unresolved with multiple competing perspectives on these topics.

Contextual Notes

Participants reference technical concepts such as standing wave ratio (SWR) and input impedance, indicating that the discussion relies on specific definitions and assumptions about antenna behavior and efficiency. Some mathematical steps and implications regarding resonance are not fully explored.

darrink1
Messages
2
Reaction score
0
How does a Radio Antenna Work?
I'm trying to get a grasp of the physical mech.

You generate an AC signal on a conductor (i.e. at 30mhz)
The free electrons on the skin of the conductor osc. back/forth at 30mhz.
The acceleration / decleration of the free electrons causes photons to be released from the free electrons (Photons being the E field)?
The acc / decl will only be large enough to cause photons to be released, if the conductor is long enough to accommodate at least 1/4 wavelength?
 
Physics news on Phys.org
Photons are "released" anytime an electron oscillates, regardless of the length of the antenna. The only difference is the efficiency with which electrical power is converted into EM radiation. A better antenna -- with the correct length for the frequency in use -- is a more efficient radiator.

- Warren
 
I take it you're discussing transmitters, how does a receiving antenna work?
 
chroot said:
Photons are "released" anytime an electron oscillates, regardless of the length of the antenna. The only difference is the efficiency with which electrical power is converted into EM radiation. A better antenna -- with the correct length for the frequency in use -- is a more efficient radiator.

- Warren

When you say "efficient" do you mean, that one antenna design vs another may generate more photons, or that the photons shoot off in a direction that makes them more usable for the receiver?
 
People don't really think of radio-frequency radiation in terms of discrete particles -- they typically use the wave model instead, as it's much easier to use. An efficient antenna produces a large-amplitude EM wave for a given feed power, and produces little heat. An inefficient antenna produces a small-amplitude EM wave for the same feed power, and converts most of the power into heat.

- Warren
 
Here's a reasonable intro to antennas:

http://en.wikipedia.org/wiki/Antenna_(radio)

By "efficiency", we mainly are referring to the "radiation efficiency" of the antenna, which is how much power is actually radiated into the far field and beyond, versus what the input power to the antenna is. If you plot the input impedance of an antenna versus frequency, you will see that it has a very reactive impedance at frequencies away from its resonance(s), which means that the power is not being launched off the antenna. At the resonance(s), you get a mostly real input impedance, which means that the power is going away somewhere, and that somewhere is mostly radiation away from the antenna. The main resonance for a "half-wave dipole" antenna is where each of the two dipole elements is 1/4 of a wavelength in free space. The main resonance for a "quarter-wave monopole" is where the single monopole element (usually vertical) is 1/4 of a wavelength, placed above a ground plane. The input impedance of a half-wave dipole antenna at resonance is about 75+j0 Ohms.

It is common to use a Standing Wave Ratio (SWR) meter when tuning up antennas. An SWR of 1.0 means that the antenna is perfectly matched to the feed amp and coax, and the radiation efficiency is 1.0. SWRs of >1.0 mean that there is a mismatch, and you are losing radiation efficiency.
 
What decides in a material what frequenzy the light waves emitted after it absorbs a photon?

It doesn't send out the same light frequenzy as it absorbs, and some goes to produce heat. I wonder what in the material that decides it.
 
Oh, and as far as receiving, the same resonance issues apply. It's just that when receiving, the currents induced on the antenna by the passing EM field cause a terminal voltage at the feedpoint of the antenna, which generates a propagating EM wave down the coax to the receiver's input amp circuit. Of course, these receive signals vary tremendously in amplitude, so the receive circuit will use Automatic Gain Control (AGC) to deal with the large dynamic range, and will generally use low-noise circuit design techniques (especially sharp bandpass filters) to be able to recover faint receive signals.
 
billiards said:
I take it you're discussing transmitters, how does a receiving antenna work?
Take the same equations, but everywhere you see a "t" write "(-t)". :biggrin:
 

Similar threads

Undergrad How Do Radio Antennas Function in Quantum Mechanics?
  • · Replies 4 ·
Replies
4
Views
3K
Undergrad How does an antenna receive and transmit radio waves?
  • · Replies 2 ·
Replies
2
Views
4K
Understanding Radio Waves & Oxygen Absorption at 60GHz
  • · Replies 1 ·
Replies
1
Views
2K
Graduate Estimate of photons/electron/cycle for radio antenna?
  • · Replies 7 ·
Replies
7
Views
4K
High School How does the hydrogen line spectrum work with only one orbit?
  • · Replies 10 ·
Replies
10
Views
3K
Graduate Can one photon be heard by multiple listeners on a radio station?
  • · Replies 27 ·
Replies
27
Views
3K
Radio Antennas and Young's Double slit
  • · Replies 8 ·
Replies
8
Views
5K
How Can We Optimize Antenna Design to Harness Radio Waves Efficiently?
  • · Replies 6 ·
Replies
6
Views
2K
Cell Phone Tower Communication: How Does it Work?
  • · Replies 1 ·
Replies
1
Views
3K
Graduate Can an Atom's Valence Electrons Be Used as a Radial Antenna?
  • · Replies 3 ·
Replies
3
Views
2K