[TowerTalk] Receive Verticals

[Roger Parsons]

I have made a receiving four square array using 25' masts with top loading much as described by W8JI. The verticals and ground systems are pretty much identical, the only significant difference being that two are on what passes for soil in northern Ontario, one is on rock, and one has its feet in shallow water.

Without any loading all four of them resonate at about 4 MHz. I added series inductance and resistance to bring the resonance to ~1850 kHz and the feed impedance to 75 Ohms. With exactly the same components in each, one three resonated at 1900 kHz and the wet one at 1850 kHz. Obviously I can add a bit more inductance to the three but I really can't understand why they should be so different. It's not the components as I have tried moving them between verticals. It's not the basic vertical as otherwise the unloaded resonances would also be different. I think the grounding is adequate and similar as the resistor required to produce 75 Ohms feed impedance is the same in each case.

The antennas are about 500' from any other antenna and are arranged with quarter wave spacing.

Any thoughts?

Thanks
Roger VE3ZI