Antenna Height & Wavelength | Amplitude Modulation

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Discussion Overview

The discussion revolves around the relationship between the height of transmitting antennas and their wavelength, particularly in the context of amplitude modulation. Participants explore the implications of antenna height on signal modulation and radiation patterns, while also touching on terminology related to antennas.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Meta-discussion

Main Points Raised

  • One participant seeks clarification on the professor's statement that the height of the transmitting antenna should be a multiple of "one fourth the wavelength," expressing confusion about the relationship between antenna height and wavelength.
  • Another participant notes that the rule about antenna height primarily applies to horizontal dipole antennas, suggesting that ground can act as a passive element affecting impedance and radiation patterns.
  • A different viewpoint suggests that the professor may have been referring to the length of radiating elements rather than the height above the ground, indicating that both factors influence the radiation pattern.
  • Some participants discuss the terminology differences between "antenna" and "aerial," with varying opinions on common usage among different regions and communities.
  • There are comments on the challenges of constructing efficient antennas at lower frequencies, highlighting practical considerations in antenna design.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the professor's statement regarding antenna height and wavelength, and there is no consensus on the terminology used for antennas versus aerials. The discussion remains unresolved regarding the precise relationship between antenna height and wavelength.

Contextual Notes

Some limitations include the dependence on specific types of antennas and the context in which the height-to-wavelength relationship is applied. There are also unresolved aspects regarding the definitions of terms used in the discussion.

Who May Find This Useful

Individuals interested in antenna design, radio communication, and terminology used in the field of electronics may find this discussion relevant.

arvik
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Hey guys, professor at college just completed teaching amplitude modulation and other stuff.Well while explaining need for modulation he said that height of transmitting antenna should be a multiple of "one fourth the wavelength" and so it is required to modulate the signal to higher carrier frequency.
Can somebody explain just briefly how we get the relation between height of antenna and wavelength?I tried searching for it on the net but couldn't find any xplanation in regards to it.
thanks.
 
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It depends on the type of antenna and you can compensate for breaking the rule somewhat.
IIRC the rule applies mostly to horizontal dipole where the ground can work as an passive element to the driven element changing the impedance and radiation pattern.
An end feed vertical has the opposite constraint.
The end needs to be at the ground or you need to construct a ground plane.

A good source for antenna design is the ARRL Antenna Handbook.
(ARRL = American Radio Relay League)
 
arvik said:
Hey guys, professor at college just completed teaching amplitude modulation and other stuff.Well while explaining need for modulation he said that height of transmitting antenna should be a multiple of "one fourth the wavelength" and so it is required to modulate the signal to higher carrier frequency.
Can somebody explain just briefly how we get the relation between height of antenna and wavelength?I tried searching for it on the net but couldn't find any xplanation in regards to it.
thanks.

I think the prof was talking about the length of the radiating elements, not the height above the ground plane. Both affect the radiation pattern, but the quarter wavelength refers to the resonant length of each half of a dipole antenna, or the single element of a monopole antenna. This wikipedia page is a good intro to antennas, with plenty of helpful links:

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

And here is a recent PF thread where we talked about antennas a fair bit:

https://www.physicsforums.com/showthread.php?t=210178


.
 
Here is some height above the ground stuff.
Starts on page 5.
http://www2.arrl.org/FandES/field/regulations/local/antplnr.pdf
 
Last edited by a moderator:
In the tradiational PF thread going off at a tangent mode.

The wiki article says that antenna / aerial means a rigid vs stiff wire but mean the same in British English.
I always used antenna for a single element and aerial for the entire system, mutliple dipoles, reflectors etc. Is this common usage?
 
Welcome to short attention span theater.:smile:

Don't know.
Personally, I'm inclined to think of aerial as archaic usage, at least in the US.
For those times when I need to be more specific than antenna I name the type.
 
mgb_phys said:
In the tradiational PF thread going off at a tangent mode.

The wiki article says that antenna / aerial means a rigid vs stiff wire but mean the same in British English.
I always used antenna for a single element and aerial for the entire system, mutliple dipoles, reflectors etc. Is this common usage?

At least among US HAMS (and the EEs that I work with), antenna refers to the whole thing, and we use the term "element" when referring to a piece of the antenna.
 
Mmmmmmmmmmm... love the concept of getting a 198kHz antenna a quarter wavelength up...
 
zeitghost said:
Mmmmmmmmmmm... love the concept of getting a 198kHz antenna a quarter wavelength up...

Yep, as you get to lower frequencies, the size of an efficient antenna can get to be pretty challenging!
 

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