Radio waves received at distance <1 wavelength

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Discussion Overview

The discussion revolves around the behavior of radio waves received at distances less than one wavelength from the transmitter, particularly in the context of AM waves with a wavelength greater than 50 meters. Participants explore the implications of proximity on signal strength and potential effects on the receiver.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the signal received at a distance of less than one wavelength differs from that received at a greater distance.
  • Another participant suggests that the signal will be stronger when closer and weaker at further distances, without delving into near field/far field theory.
  • A participant notes that the behavior of the signal may depend on the receiver's antenna, indicating that coupling between the transmitter and receiver antennas could lead to potential damage to the receiver.
  • There is a challenge regarding whether the proximity of the receiver to the transmitter (less than one wavelength) is relevant, suggesting that tuning the transmitter could still damage the receiver even at greater distances.
  • Another participant elaborates that a high Q tuning of the receiver element could lead to destruction at some distance, but emphasizes that significant coupling and minimal tuning could cause damage in the very near field due to high induced currents.

Areas of Agreement / Disagreement

Participants express differing views on the relevance of distance in relation to one wavelength and its impact on signal strength and potential damage to the receiver. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

There are limitations regarding the assumptions made about antenna coupling, the definitions of near field and far field, and the specific conditions under which damage may occur.

jimmylegss
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So let's say a radio station sends out AM waves with a wavelength of like >50m. You are standing with a receiver at a distance of <25m, what happens to the signal? Is it different or the same as if you were standing a longer distance away then 1 wavelength?

Thanks
 
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jimmylegss said:
Is it different or the same as if you were standing a longer distance away then 1 wavelength?

without getting into the complexities of near field/far field theory

the signal will just be stronger closer in and weaker the further out you go

Dave
 
It will depend on your receiver's antenna.
If the RX antenna couples to the TX antenna it might deliver sufficient energy to destroy the RX.
It could also distort the radiation pattern of the TX antenna.
 
But it has nothing to do with the fact that rx is closer then 1 wavelength from tx? So you could tune up tx enough to destroy rx even if they are more then 1 wavelength away from each other?
 
jimmylegss said:
So you could tune up tx enough to destroy rx even if they are more then 1 wavelength away from each other?
You could tune a RX element with high Q to destroy the RX at some distance from the TX element. But it takes little coupling and no tuning to destroy the RX if you are in the very near field since induced currents in close proximity can be very high.
 

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