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Ground Noise .. Sky Noise .. - RF Cafe Forums
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| Graham
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Post subject: Ground Noise .. Sky Noise ..
Posted: Sat Nov 05, 2005 12:41 pm
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| Colonel |
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Joined: Fri Sep 02, 2005
7:25 pm
Posts: 34
Location: Hampshire UK
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I think I came across a link to this info, from
this site, once before, But I have lost it now.
This is about how much noise voltage from sky noise
and ground noise can be assumed to be present for
various frequencies. In this case I need to figure
how much noise signal would arrive at a receiver
input (for a given antenna gain) for a VHF antenna
exposed to both ground and sky noise at sea.
The motivation is to trade off front-end gain
for improved intermod performance for a VHF receiver
used on board ship in the face of awesome other
RF. There is no point in having a noise figure so
low it would be useable at the edge of the galaxy.
I need to know the amount of earth noise + sky noise
common at VHF. Does anyone know where to look for
this?
Thanks
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n2hmm |
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Post subject: Hot earth, cold sky
Posted: Sat Nov 05, 2005 2:40 pm
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Take a look at this link, this might help.
http://ourworld.compuserve.com/homepage ... sky_p3.htm
Also in the Radio Engineers Handbook there is
a plot of look angle vs frequency. I thought I had
a soft copy of it but I misplaced it. You
are right in assuming that you can have a system
noise temeprture that is quieter than what the antenna
sees expecially in the VHF band. GL
John
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Graham |
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Post subject:
Posted: Sat Nov 05, 2005 6:21 pm
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| Colonel |
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Joined: Fri Sep 02, 2005
7:25 pm
Posts: 34
Location: Hampshire UK
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Thanks much n2hmm. That graph will be useful in
other situations too.
It takes care of the
sky part of it anyway. Ground is just 290K I think.
I know that on the ground (OK - on the sea for that
matter), most antennas can see the horizon. Its
only those deliberately under-illuminated dishes
that only see sky. Does not apply at all to VHF,
and I think in most urban / city situations this
noise is small compared to the man-generated racket.
G
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Posted 11/12/2012
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