The ellipse is the area clear of any reflecting obstruction above ground. I don't see a need to tie the ground plane extent to the ellipse area. Although theoretically keeping the ellipse clear should suffice to meet the NSA curve, I wold be concerned about the fence near the perimeter, regardless of its orientation relative to the major axis. Before risking the time and expense of building the OATS, why not try a quick site attenuation at the place you plan on building the OATS, and another ten meters further away if that is possible. I don't think height surveys are necessary here, the main thing is to see how many dB different the planned site attenuation is from the one further away.
From: [email protected] Reply-To: [email protected] List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] Date: Wed, 18 Jun 2003 20:13:25 EDT To: [email protected] Subject: Question about OATS Hello, I'm building an open area test site, and have some questions about the ellipse and ground plane. I'm following ANSI C63.7:1992. I have used several OATS and done site attenuation before, but this is the first time building one from the ground up. I'm building a 10 Meter OATS with a 14 foot turntable. Figure 1 in ANSI C63.7 says that the minor diameter of the ellipse shall be 17.3 Meters and the major diameter shall be 20 meters for a 10 meter site. For the ground plane, Table 1 in ANSI C63.7 says for a 10 meter site, the width shall be 12 meters and the length shall be 15.3 meters. The corners of the ground plane will be outside the ellipse. Is this ok, or should the ground plane be smaller, to fit inside the ellipse? What would be the minimum ground plane size I could use for this 10 meter site with a 14 foot turntable? Also, there is a chain-link fence running parallel with the proposed site, but the fence is just outside the ellipse. Would there be any problems with site attenuation? I can alter the ellipse so the site is not exactly parallel with the fence. (Antenna would be somewhat diagonal to the fence) Would that help avoid any problems? Thanks in advance for any input you may have. Tim Pierce EMC Engineer
