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Simple Baluns in Parallel Probes for Time Domain Reflectometry

1993; Wiley; Volume: 57; Issue: 3 Linguagem: Inglês

10.2136/sssaj1993.03615995005700030006x

1435-0661

Egbert J. A. Spaans, John M. Baker,

Microwave Engineering and Waveguides

Soil Science Society of America JournalVolume 57, Issue 3 p. 668-673 Division S-1—Soil Physic Simple Baluns in Parallel Probes for Time Domain Reflectometry Egbert J. A. Spaans, Corresponding Author Egbert J. A. Spaans n/a@.dne Soil Science Dep.Corresponding author.Search for more papers by this authorJohn M. Baker, John M. Baker USDA-ARS, 1991 Upper Buford Circle, Univ. of Minnesota, St. Paul, MN, 55108Search for more papers by this author Egbert J. A. Spaans, Corresponding Author Egbert J. A. Spaans n/a@.dne Soil Science Dep.Corresponding author.Search for more papers by this authorJohn M. Baker, John M. Baker USDA-ARS, 1991 Upper Buford Circle, Univ. of Minnesota, St. Paul, MN, 55108Search for more papers by this author First published: 01 May 1993 https://doi.org/10.2136/sssaj1993.03615995005700030006xCitations: 53AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract Time domain reflectometry (TDR) is used for the simultaneous determination of soil moisture content and electrical conductivity (EC). Limitations of parallel probes compared with coaxial probes have been signal losses in the antenna wire leading to the probes, and the required use of an expensive balun. In addition, signal attenuation in the balun hampered accurate EC determination. We describe a balun that avoids these limitations. It is a 1:1 balun, which means that it converts the electrical field from unbalanced to balanced, but no impedance transformation takes place. Consequently, this balun does not attenuate low-frequency signals, which is inherent to commonly used commerical 1:4 baluns. The balun is inexpensive and easy to fabricate, and is attached directly to a parallel pair of waveguides. This permits a system with coaxial transmission line from the TDR to the parallel waveguides. For soil moisture content determinations, the new balun performs at least as well as a conventional balun. Furthermore, EC of NaCl solutions determined from the TDR trace showed excellent agreement with EC measured with a conductance meter. Citing Literature Volume57, Issue3May-June 1993Pages 668-673 RelatedInformation