Re: [amsat-bb] Atmospheric attenuation at 2.4Ghz?

["Dr. Jim Akers" <jakers@xxxxxxxxxxxxxxx>]

Tony,

After being retired for a number of years, I can't find the ref material
for this topic. (It's probably in one of those boxes my XYL is always
after me to dispose of.) Let me tell you what I think I remember.

The attenuation is a function of a number of things including but not
limited to the following:

Frequency

Look angle above the horizon

Humidity

Height above sea level

As I recall, the attenuation around 2.4 Ghz looking at the horizon, which
would be the worst case, at sea level and with moderate humidity is less
that 0.001 db/km.  Even with high humidity, it doesn't increase
significantly. Certainly not an order of magnitude.  Even for this case if
you looked at 100 km, the attenuation would only be around .01 db.
Variations on look angle, and height above sea level would only reduce
this value.

The first big attenuation spike comes around 22 Ghz...maybe a little above
and is due to H2O resonance.  The next one is around 64 Ghz and is due to
O2 resonance.

While I am not an expert in this area, I belive these to be good "ball
park" numbers.

It occurs to me that a Google search might reveal numbers that you would
have more faith in.

73...Jim...W5VZF.



Dr. Jim Akers
Dept. of Electrical
and Computer Engineering
Miss. State Univ.


On Sat, 17 Jan 2004, AA2AE wrote:

> All
>
> I was wondering about the effects of the atmosphere at 2.4Ghz. Specifically,
> I thought there might be some degree of signal deffusion or other
> attenuation effects as AO-40's signal penetrated the Earths gaseous
> atmosphere.
>
> I've read that atmospheric attenuation begins to effect the performance of
> mircowave frequencies above 10 Ghz and that water vapor absorption can be
> severe at 24Ghz. But, what about 2.4Ghz? Is there any measueable effect on
> the mode-S downlink we can detect via AO-40?
>
> I would assume attenuation at 2.4Ghz would be relatively small compared to
> the higher microwave frequencies and that the effects are not as pronounced
> from the "top-side" of the atmosphere as with satellite communications, as
> the are with terrestiral propagation.
>
> Any thoughts?
>
> 73, Tony - AA2AE
>
>
>
>
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