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Normal mode helix antennas offer a solution for HF mobile operators facing significant height restrictions, such as those parking in indoor garages with limited overhead clearance. This design, adapted from concepts typically applied to VHF/UHF rubber duck antennas, allows for extremely shortened HF radiators that remain effective for county hunting and general mobile operation. The resource details the construction of a 20-meter helix antenna, approximately 10 inches long, wound with #14 AWG THHN wire on a 1 1/2-inch CPVC form, mounted on a standard 3/8 x 24 antenna stud. Mark Herson, _N2MH_, shares his experience developing these antennas, including initial research from the _RSGB VHF UHF Manual_ and practical winding experiments to establish the relationship between turns and resonant frequency. He provides coil data for various frequencies, emphasizing that these measurements were taken with an _MFJ-259a_ antenna analyzer and are dependent on the vehicle's grounding system. Despite their shortened nature, N2MH confirms the antennas' operational effectiveness, citing contacts with KL1V in Alaska on 20 meters and E-skip contacts on 10 meters. The design prioritizes continuous deployment without removal, making it suitable for operators who frequently navigate height-restricted environments.

Operating a ham station often involves encountering radio frequency interference (RFI), RF feedback, or RF burns, which are frequently misattributed to poor equipment grounding. This resource meticulously dissects these assumptions, asserting that RF grounds on the operating desk often merely mask more significant system flaws. It identifies five primary causes for RF problems, including antenna system design flaws, proximity of the antenna to the operating position, DC power supply ground loops, equipment design defects, and poorly installed connectors or defective cables. The content emphasizes that issues like "hot cabinets" or changes in SWR when connecting a ground indicate substantial RF flowing over wiring or cabinets, a phenomenon known as common-mode current. The article provides detailed explanations of common-mode current generation, particularly from single-wire fed antennas like longwires, random wires, and OCF dipoles, which inherently present high levels of RF in the shack. It also illustrates how vertical antennas, lacking a perfect ground system, can excite feed lines with significant common-mode current. Through simulations, the author demonstrates how a dipole without a proper _balun_ can cause RF problems at the operating desk, showing current patterns and voltage distributions on feed line shields. The discussion extends to the proper application of _RF isolators_ and _ferrite beads_, clarifying their role in modifying common-mode impedance on cable shields and cautioning against their use as a band-aid for fundamental system defects. The resource advocates for correcting the actual source of RF problems, such as antenna system issues or poor connector mounting, rather than relying on internal shack grounding or isolators. It highlights that properly functioning two-conductor feed lines, like coaxial or open-wire lines, should result in minimal RF levels at the operating position, even without a desk RF ground. The author shares personal experience, noting that his stations since the late 1970s have operated without RF grounds at the desks, relying instead on proper antenna system design and feed line integrity.

This document details the construction of a multi-band end-fed antenna, suitable for situations with limited space for larger antennas. The design utilizes a 1:49 to 1:60 impedance transformer to match a half-wave wire antenna fed at one end. Compared to a traditional dipole, this antenna resembles a highly unbalanced Windom antenna with one very long leg and a virtual short leg. The design eliminates the need for radials but relies on the coax cable shield for grounding. The document recommends using at least 10 meters of coax and installing a common mode filter at the entry point to the shack for improved performance.