Modulation in high frequencies and antennas

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Discussion Overview

The discussion centers around the relationship between modulation at high frequencies and antenna design, particularly focusing on the implications of wavelength and antenna size. Participants explore whether there are specific rules or equations that govern this relationship, and the role of modulation in selecting carrier frequencies.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants suggest that modulating signals at high frequencies is preferred because the wavelength is small compared to the length of the antenna.
  • Others clarify that efficient antennas, such as half-wave dipoles and quarter-wave monopoles, are designed based on the relationship between antenna length and wavelength.
  • One participant argues that modulation is not directly related to antenna design, emphasizing that the carrier frequency and antenna are connected but distinct concepts.
  • Another participant points out that while antenna size can be a consideration, the primary reasons for frequency selection involve wave propagation characteristics, such as the ability to transmit over the horizon or interact with the ionosphere.
  • There is a reiteration that the length of efficient radiating elements should not exceed the wavelength of the transmitted signal.

Areas of Agreement / Disagreement

Participants express differing views on the significance of modulation in relation to antenna design, with some asserting a connection while others argue it is minimal. The discussion remains unresolved regarding the primary factors influencing frequency selection.

Contextual Notes

Participants have not reached a consensus on the relationship between modulation and antenna size, and there are unresolved assumptions regarding the definitions of modulation and its implications for antenna design.

dervast
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Hi to everyone. I have heard that we usually prefer to modulate signals at high frequencies so the wave length is small compared to the length of the antenna. Is there any rule or equation that implies this requirement?
 
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To be an efficient radiator, an antenna will generally be a half-wave dipole or a quarter-wave monopole. That is, a dipole antenna will have two opposed elements, each a quarter-wavelength long. A monopole will have a single radiating element a quarter-wavelength long, over some ground plane or set of ground elements.

http://en.wikipedia.org/wiki/Antenna_(radio)
 
dervast said:
Hi to everyone. I have heard that we usually prefer to modulate signals at high frequencies so the wave length is small compared to the length of the antenna. Is there any rule or equation that implies this requirement?

Modulation has little to nothing to do with the antenna. The carrier frequency and the antenna are related as berkeman pointed out.
 
Averagesupernova said:
Modulation has little to nothing to do with the antenna. The carrier frequency and the antenna are related as berkeman pointed out.
I agree with u.. the antenna has nothing to do withthe modulation scheme. I was talking about modulation describing that we modulate signals in high frequencies
 
So you are saying that the reason we use certain frequencies in the spectrum for the carrier is to keep the antenna size in check? The main reason we use the ones we do is propagation of the wave. Some signals we want to go over the horizon, some we don't. Some signals we want refracted off the ionosphere, some we don't. However, there ARE cases were antenna size is a consideration. I would not say it is the main reason. Throwing the word modulation in there has thrown me off.
 
dervast said:
...wave length is small compared to the length of the antenna. Is there any rule or equation that implies this requirement?
As Berkeman has implied, the antenna length of efficient radiating elements is not larger than the wavelength of the transmitted signal.
 

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