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

 Post subject: Ground Noise .. Sky Noise ..

Posted: Sat Nov 05, 2005 12:41 pm 

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

 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

 Post subject:

Posted: Sat Nov 05, 2005 6:21 pm 

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