Report: Frequently Observed - Parasitic Phenomena

In a recent response to Mark Persons' story titled "A Visit to 'Shine 800 AM'", Ben Dawson, consulting electrical engineer and co-founder of Hatfield & Dawson Consulting Electrical Engineers, has shed light on a misinterpretation about Kintronic Labs Senior Staff Engineer Jim Moser's comment regarding parasitic elements in directional AM arrays.

Parasitic elements in directional arrays can be either grounded or loaded with a passive load having a suitable impedance. This technique, while not common in the U.S., has been employed in quite a few high power arrays outside the western hemisphere, as Moser stated. This approach is particularly useful for linear arrays with high RSS/RMS ratios, as it increases stability.

Historically, grounded parasitic arrays, where towers are simply grounded, were rare due to the lack of control over current magnitude and phase. However, with advancements in technology, arrays with parasitic towers loaded with resistance, reactance, or a combination are common. Before the moment method (MM) analysis techniques became common, predicting the current values in grounded parasitic arrays could be challenging.

Ben Dawson himself has used this technique in a recent installation and for both new designs and repair projects. One of his notable works includes the design of a 2 MW, 4-element array. His colleague Ron Rackley was uncertain about the MM model, so they constructed the top of the parasitic towers in 10 ft. sections to allow for removal if necessary.

Rackley's application to the FCC was significant in allowing this technique to be more widely used. The FCC now allows the transmitter output power to include both the radiated power and the power terminated in a resistive load on the parasitic tower. This technique is beneficial in certain scenarios beyond linear arrays with high RSS/RMS ratios.

Despite its rarity in the U.S., this type of parasitic array is becoming more common, especially since the FCC eliminated the discrete transmitter power output rules. It is believed that this is the type of parasitic array that Moser at TWR was referencing.

Ben Dawson and his team at Hatfield & Dawson Consulting Electrical Engineers are involved in consulting, planning, and implementation services such as photovoltaic systems, battery storage, and electric vehicle charging stations. Their expertise in parasitic array design and implementation could potentially contribute to its increased usage in the U.S. and beyond.