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Ground Noise .. Sky Noise .. - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


Graham
 Post subject: Ground Noise .. Sky Noise ..
Posted: Sat Nov 05, 2005 12:41 pm 
 
Colonel
User avatar

Joined: Fri Sep 02, 2005 7:25 pm
Posts: 34
Location: Hampshire UK
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


 
   
 
n2hmm
 Post subject: Hot earth, cold sky
Posted: Sat Nov 05, 2005 2:40 pm 
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


 
  
 
Graham
 Post subject:
Posted: Sat Nov 05, 2005 6:21 pm 
 
Colonel
User avatar

Joined: Fri Sep 02, 2005 7:25 pm
Posts: 34
Location: Hampshire UK
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




Posted  11/12/2012

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