80m Antenna Design

[ARDF Coordinator]

All 80m antennas used during the 2021 USA ARDF Championships (except for foxoring) were center-fed tuned vertical dipoles which required no ground radials --- thus avoiding that trip hazard and antenna setup step.

The basic design is described here: https://openardf.org/ardf-open-equipment-project/open-80m-fox-antenna/

The vertical dipole design has been used regularly at local ARDF practices for almost 2 years now and has worked reliably. I would call the antenna design "experimental" but pretty well proven, given that more than 20 antennas of this design have been constructed, tested, and shown to work reliably.

The sprint antennas used the same dipole design but with shortened radiating elements of about 1 meter length, thus making the sprint antennas 2 meters high. The shortened radiating elements required a slightly higher capacitance for C101 in order to achieve resonance for proper antenna matching. The latest PCB design (OSHPark) provides an additional C101 mounting holes that can accommodate a ~10pF - 20pF capacitor to be added in parallel. The sprint antennas were constructed on two 1-meter lengths of 6mm fiberglass rod that comes pre-terminated with brass screw-together fasteners. Enough rods to build ten sprint antennas is provided in a single 66-foot length (or two 33-foot lengths) "wire puller" product similar to this one:  https://www.amazon.com/dp/B07WFMRRNX/ref=cm_sw_em_r_mt_dp_3B4PQCBSF0P7W11QYECN?_encoding=UTF8&psc=1 I prefer the fiberglass rods to be at least 6mm diameter, but those can be hard to find. Thinner fiberglass makes the antennas "floppier", but lighter and still very usable for this application. By soldering the radiating element connections to the brass screw connectors, the sprint antennas can be disassembled by unscrewing them in the middle, making them 1 meter long for easy transport. A nylon strap mounted 1/4 down from the top of the antenna provides an easy and reliable way to attach the antenna to a small tree, shrub, or post.

[Vadim Afonkin]

Been using and pushing this deal gn for last 10 years :)

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