Design Notes: Vertical Feedpoints

When I was outside yesterday investigating the problem with the verticals, one of the first things I did was to check their feedpoint impedances at resonance. This constitutes the first "Y" in the diagnostic logic tree, telling me whether or not the problem is with the aluminum verticals. When I checked with the MFJ 256B antenna analyzer, they were both perfectly tuned to 7.1 MHz, exhibiting zero reactance and 40 Ohms of impedance. This is where I set them after cleaning them over a month ago. Which means they are 90% efficient. 

It is likely that the 4 Ohms of ground loss is partially due to the means through which I connect the ground systems to the coaxial feedline. This connection is a bolt squeezing two large ring terminals (soldered to the ends of 1/4” copper tubing loops) sandwiched between which being wires leading to the coax shields and static bleed RF chokes. On the Northeast vertical, this connection by necessity gets swamped twice a day by saltwater. Not having a NSF grant, I am using what hardware is available in The Parts Department. And in this instance that means a steel wing nut to compress the connection. And that sumbitch gets rusty immediately after deployment. 

The center conductor connection can also stand improvement. Or perhaps replacement after 3 years of service. Its design merely replicates the design I came up with for the portable vertical. What happens is the center conductor connection serves two purposes. It acts as a mechanical stop for the aluminum tube in the PVC insulator tube. While also making the electrical connection between the center of the coax and the tube. This is done by inserting a stainless steel screw through the aluminum and PVC tubes, making sire to drill the hole through the PVC tube larger than that required for the stainless steel screw. This allows for the lacing of two aluminum standoffs on either side of the screw which, when a nut is run-down on the screw, squeeze against the aluminum vertical tube from either side of the the PVC tube. The center conductor of the coax is tightened down on the stainless steel screw with a second nut. This constitutes the electrical connection to the aluminum vertical. Naturally, I am using steel nuts which quickly corrode. And after years of service, the aluminum standoffs are in need of burnishing. Or I can just redesign the whole connection, which is what I did in the tilt-over design.

In the tilt-over contraption, we no longer require the PVC insulator tube to support the vertical tube and ground ring, as originally devised in the portable and elevated phased vertical applications. Instead, the vertical extends below the base PVC insulator so that a brass machine screw and wing nut can provide electrical connection to the center of the coax. To prevent vertical slippage, a hitch pin passes through the aluminum and PVC tubes at the top of the base insulator.

I would like to relocate the verticals deeper into the Marsh. Moving them over to the South a bit, and then deeper into the Marsh to the East. To do this what I would do is not touch either vertical; leave them right where they are. Instead, I would meticulously and anal-compulsively build two ground radial fields out of aluminum electric fence wire. This would mediate the corrosion problem if aluminum hardware was used at the bases of the verticals,

BILL W1ZY