Antenna Construction Ideas (6 Meter Vertical Build)

Improving ionospheric conditions and a radio otherwise useless on 6 meters without an antenna (aren’t they all?) motivated me to whip up a vertical that would sit within the limits of the HOA on my flat roof. You may not have the same interest in mind, but perhaps some of the construction details may help in a project you would like to do.

First, I scrounged pieces of 5/8-inch and 7/16-inch that telescoped and was 5 feet or so in length. Next, I rounded up a couple of 10-foot lengths of 1.25-inch PCV tubing, three T joints and 4 end caps. No one complained when I sawed the pieces in half in the parking lot to fit in my car. I also gathered some heavy gauge wire, ¾ inch copper plated steel strap with holes, a length if 1/8-inch brass rod, a 100pf capacitor from a neighbor ham, SS nuts bolts and washers, PCV glue, UV spray paint and a very strange PCV fitting. A lot of this stuff was on hand around the house, but some was obtained while engineering as I went roaming the plumbing, electrical and nut/bolts sections of the local hardware store.

FIG1

The frame was assembled with six 30-inch pieces of 1.25-inch PCV in an H shape on a flat floor with the third T located vertically to mount the driven element (FIG1). The base is painted with UV resistant paint when assembly is finished. For other projects I’ve used threaded rather than glued junctions so it can be dismantled. Using larger tubing that could be filled with pea gravel for stability has been successful as well. Electrical PVC, the gray stuff, is usually UV resistant and often found in larger sizes and heavier gauges.

FIG2

The ground plane is installed next. A 5-foot piece of ¾-inch copper plated steel strap (used by plumbers to support pipes) was run through the middle with a ¼-20 1-inch SS bolt exiting the center T fitting for feedline connection (FIG2). Wire conductors branch out at the T junctions extending to the ends of the legs (FIG3). Possibly using the copper plated strap instead of wire would make construction easier. While the length of these “radials” can affect matching, it is not particularly important at this stage.

FIG3

FIG4

You have top get lucky once in a while. While roaming the hardware store with sample pieces of aluminum tubing and PVC, I stumbled on a fitting designed to join irrigation tubing that the ID fit a ¾-inch piece of PCV perfectly and which was a close fit for the 1 ¼-inch ID of the PVC of the main structure on the outside. After sanding the fitting, it fit into the 1.25-inch PCV very nicely. Next, a wire was attached to the vertical aluminum element, parts assembled and epoxied to join and seal the parts from weather (FIG4). The wire was then attached to another ¼-20 SS bolt to provide feedline connection to the driven element.

A short PVC stub could be installed instead of the vertical element to mount other antennas like commercial UHF/VHF verticals. In most cases the ground plane wiring would then serve no purpose.

Electrically it is pretty rough at this point and it’s time to make it work. The first step is to measure and adjust the driven element length for minimum SWR. In this case it was 2.8 to 1 SWR, expected, but not very good. I used an AIM 4170 VNA for measuring purposes. The results of the VNA scan can be saved and imported to SimSmith software where it’s quite easy design an input match. The Figure 5 shows SimSmith resolving the SWR to 1.007 to 1 with an ideal high pass L match.

Figure 5

FIG 6

However, that is an ideal match and components with the exact values calculated usually do not exist. Using the VNA to measure components at the frequency in use, a doorknob capacitor that actually measured 100pf was found and a coil constructed from 1/8-inch brass rod that was close to 75nH was fabricated. Mini Ring Core Calculator software does air core calculations as well as toroid cores and was very helpful in sizing the inductor. The L match resulted in a 1.06 to 1 SWR (FIG 6).

It requires a 6-meter opening to report performance. A couple of days after placing the antenna on my flat roof I heard some signals on the band. This antenna must work as I made several contacts, the first three were with Argentina and Chile. I hope my use of materials, hardware and computer programs might help you in your antenna projects.

EST N9MW 2-23-24
TNX W0IVJ for software advice