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

RF Cafe Forums closed its virtual doors in late 2012 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2012, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. Regardless, there are still lots of great posts in the archive that ware worth looking at. Below are the old forum threads, including responses to the original posts. Here is the full original RF Cafe Forums on Archive.org

-- Amateur Radio

-- Anecdotes, Gripes, & Humor

-- Antennas

-- CAE, CAD, & Software

-- Circuits & Components

-- Employment & Interviews

-- Miscellany

-- Swap Shop

-- Systems

-- Test & Measurement

-- Webmaster
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. https://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