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WAOK-AM Uses Method of Moments Proof
The antenna system employs Kintronic Labs VSU-1 voltage sampling units.
Following the completion of the tower models the final segment data was input into the MININEC Broadcast Professional DA model. The drive impedances, power division and operating parameters for the required pattern were derived using FCC database theoretical information for operational constants. Table 5 shows the final computed results.
|Tower||Model Current Pulse||Model Voltage Magnitude (amperes)||Model Voltage Phase (degrees)||Model Drive Impedance (ohms)||Model Drive Power (watts)|
|1||1||1218.04||2.8||129.67 - j335.46||1487.32|
|2||20||1160.18||82.7||81.076 - j411.30||620.97|
|3||39||573.908||22.2||74.466 - j217.49||464.129|
|4||58||593.784||-85.1||72.681 - j102.29||1627.58|
|Table 5. Final computed results|
Now taking into consideration the measurement derived series and shunt tower base reactances the corrected self impedance at each of the VSU measurement locations was computed using the WCAP network analysis program developed by Jerry Westberg. With equal length sample lines the operating parameters are equal to the base sampled voltages and phases. The final derived operating parameters are shown in Table 6.
|Tower||Drive Impedance at VSU (ohms)||Voltage Magnitude at VSU (volts)||Voltage Phase at VSU (degrees)||Antenna Monitor Ratio||Antenna Monitor Phase|
|1||106.92 - j267.83||1075.607||5.4851||108.1||-78.7|
|2||53.19 - j286.19||994.7057||84.1663||100.0||0.0|
|3||44.78 - j159.26||532.5942||23.3579||53.5||-60.8|
|4||56.60 - j71.77||490.1382||-77.5847||49.3||-161.8|
|Table 6. Final derived operating parameters|
At this point it was time to return to the station and adjust the array to the predicted parameters. The previous measured proof monitoring points were used as reference points for the MOM proof. Following adjustment of the array to the predicted parameters all of the measured proof monitoring points were found to yield a reduced field intensity with the MOM proof parameters. This process was accomplished in record time compared to the weeks that typically would be involved in collecting multiple radial field intensity measurements followed by an exhaustive report. As stated earlier, the MOM proof was filed on April 5, 2011, and the license was granted on June 9, 2011.
We want to affirm with anyone considering the use of these voltage sampling units that they are resilient in lightning environments as attested to by an unsolicited report from Robert LaFore, the WAOK chief engineer.
"The VSUs are indeed coping with lightning very well. I just had a tower crew on tower 3 of the WAOK array. The insides of the beacon assembly are pretty much vaporized, and the wiring to that beacon is melted and charred badly. Paint is gone on the top of the tower. At the same time we lost several microswitches at tower 3. The VSU is showing nice steady numbers night after night."
When this report was prepared we had no reports of any problems with the Kintronics voltage sampling system.
The authors thank Ron Rackley for his exceptional involvement in the development of the voltage sampling units and in his oversight of the MOM proof.
Crain is principal of M. Donald Crain, Inc, Boiling Springs, SC. King is president of Kintronic Labs, Inc., Bristol, TN.
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