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

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

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