WAOK MoM Proof Methodology

A Model VSU-1 unit installed at the base of one of the four towers in the WAOK array

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Following the installation of the voltage sampling system in the WAOK array Don Crain visited the site to conduct phase 1 of the MOM proof process. All the WAOK towers are 179.3° electrical height. Towers 1 and 2 are fixed cross-section guyed towers each having a facewidth of 30.25". Towers 3 and 4 are tapered cross-section triangular self-supported towers having a base cross section of 24.75' tapering to a cross section of 30.25" at the 290' level and having a fixed cross section of 30.25" for the top 65'. Robert LaFore, the CBS Atlanta market chief engineer, had to arrange for a tower rigger to climb one of the self-supported towers and measure the facewidth as a function of height due to the lack of any tower drawings at the station. This information was critical for the tower modeling effort required for the MOM proof.

Upon arrival at the station Crain measured the impedance of each tower with the other towers either open or shorted. Figure 2 shows the tower base installation configuration for the voltage sampling units.

Figure 2. The installation configuration of the Model VSU-1 voltage sampling units at each WAOK tower base (click to enlarge)

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A four-port network analyzer with an RF power amplifier and a Tunwall Radio directional coupler based on the technique developed by Ron Rackley was used to make the measurements as shown in Figure 3.

Figure 3. The network analyzer setup used to make tower impedance measurements (click to enlarge)

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The impedance measurements were made at the tower side of the open J-plug in each VSU unit as shown in Figure 2 with the ATU output J-plug open as well. The impedances measured for the shorted case are shown in Table 1.

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