Reg Edwards wrote:

There exist statistics of AVERAGE field strength noise levels
experienced in cities, small towns and in the open countryside. I have
forgotten where to find such statistics but Google may help.

The statistics depend very much on frequency. They vary greatly between
ELF and HF. Noise levels decrease by crudely 10 dB or 20 dB per octave
or decade increase in frequency.


ITU Recommendation ITU-R P.372-8, 'Radio Noise'. This document replaces
and updates the old CCIR Report 322, which was the source for most of
the information on radio noise in the amateur handbooks.

The paper is available as a download from ITU, but they want 36 Swiss
Francs for it (about $28):
http://www.itu.int/rec/R-REC-P.372-8-200304-I/en



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek