"K7ITM" wrote in news:1172204498.747073.7270
@k78g2000cwa.googlegroups.com:

The "noise" chapter of Sams' "Reference Data for Engineers" has some
info on noise versus frequency, from various sources; included are a
map of usual atmospheric noise levels around the world, and I believe
sky-maps of galactic noise. You can also find some of that on the
web.

A more up to date source of expected ambient noise levels is ITU-R
Recommendation P.372-8. I have summarised some of the info from that
document for HF frequencies at http://www.vk1od.net/fsm/FSAmbientNoise.htm
..

Owen