Free Space Attenuation: Understanding Radio Wave Loss

• Wannabeagenius
In summary, the attenuation of radio waves in space is not only due to the inverse square law, but also to a loss caused by the medium, which in space refers to the mass density of interstellar space. While the EM wave itself is not being attenuated, the amount of power utilized at the destination can be affected by the frequency dependence of the receiving antenna. This dependence is not directly related to free space, but is rather a factor in the antenna's functionality. Therefore, the term "free space attenuation" may be misleading.
Wannabeagenius
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

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.

I'd like to thank everybody for helping me understand this issue.

Bob

1. What is free space attenuation?

Free space attenuation is the loss of radio waves as they travel through the atmosphere. It is caused by the natural absorption and scattering of the waves by gases, particles, and other objects in the atmosphere.

2. What factors affect free space attenuation?

The main factors that affect free space attenuation are the frequency of the radio waves, the distance they travel, and the presence of obstacles such as buildings or trees.

3. How is free space attenuation calculated?

Free space attenuation is typically calculated using the Friis transmission formula, which takes into account the power of the transmitter, the gain of the antenna, and the distance between the transmitter and receiver.

4. How does free space attenuation impact wireless communication?

Free space attenuation can significantly impact wireless communication by reducing the strength of the signal and causing interference. This can result in a weaker and less reliable connection, especially over longer distances.

5. How can free space attenuation be mitigated?

There are several ways to mitigate free space attenuation, including using higher frequency radio waves, using directional antennas to focus the signal, and increasing the transmitter power. In some cases, physical barriers such as repeaters or reflectors can also be used to improve signal strength.

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