Free Space Attenuation: Understanding Radio Wave Loss

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Discussion Overview

The discussion revolves around the attenuation of radio waves in space, specifically addressing the factors contributing to signal loss, including the concept of free space and the role of the medium. Participants explore the implications of distance and frequency on radio wave propagation.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Bob expresses confusion about the attenuation of radio waves in space, questioning whether loss is due to the presence of atoms in what is often referred to as a vacuum.
  • Some participants clarify that space is not a perfect vacuum and suggest discussing the mass density of interstellar space.
  • One participant argues that there is no mechanism for a wave to experience loss in free space, citing the inverse-square law and frequency dependence of antennas as the primary factors affecting signal strength.
  • Bob contends that the term "free space attenuation" should not include frequency dependence, as he believes it does not pertain to free space itself.
  • Another participant agrees with Bob's perspective regarding the separation of frequency dependence from the concept of free space.

Areas of Agreement / Disagreement

Participants express differing views on the nature of attenuation in free space, with some asserting that there is no loss while others highlight the complexities introduced by the medium and frequency dependence. The discussion remains unresolved regarding the definitions and implications of free space attenuation.

Contextual Notes

The discussion reflects varying interpretations of what constitutes free space and how different factors, such as distance and frequency, contribute to perceived signal loss. There is ambiguity regarding the terminology used and its implications for understanding radio wave propagation.

Wannabeagenius
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Hi All,

I'm reading about the attenuation of radio waves in space and I understand that, in addition to the normal attenuation that is proportional to the inverse of the square of the distance, there is also a loss due to the medium.

This surprised me as I thought that there was no loss in space due to energy absorbed by the medium. Is this loss because space is not actually a vacuum but contains a few atoms here and there and these atoms absorb energy from the radio waves?

Thank you,

Bob
 
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Space is a pretty general term, and non of it is a perfect vacuum. That doesn't even really make sense to talk about. It is more reasonable to speak of the mass density of interstellar space. http://en.wikipedia.org/wiki/Interstellar_medium
 
Phyisab**** said:
Space is a pretty general term, and non of it is a perfect vacuum. That doesn't even really make sense to talk about. It is more reasonable to speak of the mass density of interstellar space. http://en.wikipedia.org/wiki/Interstellar_medium

But to be more precise, I'm interested in knowing what is meant by the attenuation of free space with regard to communications.

Thank you,

Bob
 
I don't know any mechanism for a wave to be lossy in free space.

And according to this:
http://en.wikipedia.org/wiki/Free-space_path_loss

It's just inverse-square law plus the frequency dependence of the receiving antenna. The EM wave itself is not being attenuated (ie no power loss).
 
kcdodd said:
I don't know any mechanism for a wave to be lossy in free space.

And according to this:
http://en.wikipedia.org/wiki/Free-space_path_loss

It's just inverse-square law plus the frequency dependence of the receiving antenna. The EM wave itself is not being attenuated (ie no power loss).

yes right, but space is never really "free space"
 
"free space attenuation" would, by definition, not include what you are talking about.
 
kcdodd said:
I don't know any mechanism for a wave to be lossy in free space.

And according to this:
http://en.wikipedia.org/wiki/Free-space_path_loss

It's just inverse-square law plus the frequency dependence of the receiving antenna. The EM wave itself is not being attenuated (ie no power loss).

I understand what is going on and the problem is semantics.

The amount of power arriving at the destination is not frequency dependent but is dependent only upon the square of the distance. This, to me, is a true loss due to distance in space.

Apparently, once a certain amount of power reaches the destination, the amount of it that is utilized is dependent upon the frequency.

Is there a logical reason why the frequency dependence is not better separated from the term free space since it really has nothing to do with free space as I see it?

Thanks again,

Bob
 
Wannabeagenius said:
Is there a logical reason why the frequency dependence is not better separated from the term free space since it really has nothing to do with free space as I see it?
Thanks again,
Bob
The frequency dependency comes only in when the antenna is considered.
So it looks like your right about that.
 
I'd like to thank everybody for helping me understand this issue.

Bob
 

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