Half wave dipole antenna physics

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Discussion Overview

The discussion centers around the behavior of a half wave dipole antenna when driven by a voltage-controlled oscillator (VCO) at a frequency lower than its resonant frequency. Participants explore the implications of using a 6.25 cm antenna at 1 GHz instead of the expected 2.4 GHz, focusing on emission characteristics and the relationship between antenna length, frequency, and electromagnetic (EM) wave propagation.

Discussion Character

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

Main Points Raised

  • Some participants propose that the antenna will only radiate at the frequency of the VCO, suggesting that using a lower frequency results in reduced efficiency without altering the frequency of emission.
  • Others argue that the EM wave is always radiated at the speed of light, regardless of the driving frequency.
  • A participant questions how the wavelength of the emitted EM wave can match the driving frequency if the electron movement is restricted by the antenna's physical length.
  • There is a discussion about the terminology used, with some suggesting that "emission rate" is not appropriate in the context of RF and antennas, advocating for the use of "frequency" instead.
  • One participant emphasizes that the oscillation of electrons at a given frequency results in very small physical movement, which may not correspond to the wavelength expected from the driving frequency.
  • Another participant expresses frustration over the labeling of the thread as advanced, suggesting that some contributors lack a fundamental understanding of the concepts involved.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between antenna length, driving frequency, and emission characteristics. There is no consensus on how these factors interact, and the discussion remains unresolved.

Contextual Notes

Some limitations in the discussion include assumptions about the definitions of terms like "emission rate" and "frequency," as well as the implications of antenna efficiency and resonance that are not fully explored.

midz99
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First time poster long time reader.

If i have a half wave dipole antenna with a certain length and I am using a VCO to drive that antenna at lower driving frequency do i get EM at the length of twice the length of the antenna but just at a slower emission rate?

example, if i have a half wave dipole antenna measuring 6.25cm and I am using a VCO to drive that antenna at only 1ghz where i should be using 2.4ghz, will that antenna still emit EM at 2.4ghz but at a rate of 1ghz?
 
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midz99 said:
First time poster long time reader.

If i have a half wave dipole antenna with a certain length and I am using a VCO to drive that antenna at lower driving frequency do i get EM at the length of twice the length of the antenna but just at a slower emission rate?

example, if i have a half wave dipole antenna measuring 6.25cm and I am using a VCO to drive that antenna at only 1ghz where i should be using 2.4ghz, will that antenna still emit EM at 2.4ghz but at a rate of 1ghz?
The antenna only radiates the frequency of the VCO. If it is of the "wrong" length, then efficiency is reduced, but frequency is unaltered.
 
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midz99 said:
If i have a half wave dipole antenna with a certain length and I am using a VCO to drive that antenna at lower driving frequency do i get EM at the length of twice the length of the antenna but just at a slower emission rate?

The EM wave is always radiated/emitted at the speed of light

midz99 said:
example, if i have a half wave dipole antenna measuring 6.25cm and I am using a VCO to drive that antenna at only 1ghz where i should be using 2.4ghz, will that antenna still emit EM at 2.4ghz but at a rate of 1ghz?

As tech99 said the emission will be poor
This is because the antenna isn't resonant for the 1 GHz frequency from the VCO
 
i think you miss understand what i meant by emission rate, each cycle back and forward of electron movement creates EM, now if the driving frequency was 2GHz then emission rate would be 2GHz. The distance an electron travels before its return trip directly corresponds to the wavelength of EM you get. but if that distance is restricted by length of the material, so it doesn't travel far enough how do you still get the same wavelength as the driving frequency?
 
midz99 said:
now if the driving frequency was 2GHz then emission rate would be 2GHz.

forget about the term emission rate ... isn't a term used for RF and antennas ... use frequency
The RF signal is emitted at the speed of light regardless of its frequency

midz99 said:
The distance an electron travels before its return trip directly corresponds to the wavelength of EM you get

no, the electrons just oscillate about a point at the given frequency. The distance they move at 2GHz is nigh microscopic in length

midz99 said:
but if that distance is restricted by length of the material, so it doesn't travel far enough how do you still get the same wavelength as the driving frequency?

that has already been answered above by tech99 and myself

BTW this thread shouldn't be labelled A for advanced, when you don't even have an understanding of the basics
Dave
 

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