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Re: Atmospheric attenuation at 2.4Ghz?



Tony,

This properly a radio astronomy question (almost).  I reached for my 2nd
ed. of Kraus, Radio Astronomy, page 7-1 where fig. 7-1 shows antenna sky
noise vs freq.  The curves do no diverge for wet vs dry until above 8 GHz
and have real noticable effects near 24 GHz (and higher).  of course this
is addressing antenna noise temp instead of attenuation but it should
follow.  The window from 1 to 8 GHz is the quietest and best for space
comm. or astronomy!  At 2.4 GHz sky  temp varies from 3K to 90K depending
on antenna elevation angle.  It varies from 3 to 10K depending on if you
are looking along the galactic plane or not (the sun makes a big noise, of
course).

Perhaps someone else can contribute some hard numbers for atmospheric
absorption at 2.4 GHz, but terrestrial foliage absorption/noise temperature
is more significant ;-)

73 Ed - AL7EB

At 07:54 AM 1/17/2004 -0500, 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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