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What to use for an underground transponder?
Roy Lewallen wrote:
Attenuation through the ground depends on the soil conductivity and dielectric constant, and the frequency. Here's the attenuation in dB/ft for two ground types and a number of frequencies: Freq MHz Avg soil(1) Vy good soil(2) 0.01 0.037 0.091 0.1 0.12 0.29 1 0.35 0.90 10 0.66 2.4 100 0.69 3.3 10,000 0.69 3.4 So if I get this right, a 2.4gHz signal in normal soil would be anttenuated 6.9 db (less than 2 "S units). In very good soil, it would be anttenuated around 34 db, which would make it difficult to receive. A Pringles can antenna has a gain of about 18db, that would certainly be enough for average soil, and might be good enough for very good soil. It also has the advantage of possibly being a 2 way link. Geoff. -- Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM New word I coined 12/13/09, "Sub-Wikipedia" adj, describing knowledge or understanding, as in he has a sub-wikipedia understanding of the situation. i.e possessing less facts or information than can be found in the Wikipedia. |
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