I read in !emc-pstc that Wan Juang Foo <f...@np.edu.sg> wrote (in <of7b89ef09.2d45a212-on48256b26.0010c...@np.edu.sg>) about 'Enclosed OATS facilities in snow country', on Tue, 18 Dec 2001: >The maximum difference between >sample means are about 23 dB around the frequencies where at one time was >the nulls (found during fair weather).
You are bound to get this 'large' variation, simply because decibels are a log scale. If you consider simple wave interference at a point, full reinforcement just increases the field strength by 6 dB, but full cancellation decreases it by -infinity dB. The presence of snow cover does not in itself affect the level of the water table. It simply creates an imperfectly-conducting ground plane over surfaces that, in better weather, are almost non-conducting. The effect of the true water table, which is normally well below ground level, depends on the depth and nature of soil cover. If there is a saturated, permeable layer, then that, too, is an imperfectly-conducting ground plane, but a better conductor than snow because its salt content is normally much higher. However, most frequencies are rapidly attenuated by soil, so the radiation may never 'see' the water table as a ground plane. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk After swimming across the Hellespont, I felt like a Hero. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
