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The G5RV antenna, a popular multi-band wire antenna, typically employs a center-fed design with a specific length of 300-ohm or 450-ohm open-wire line acting as an impedance transformer, feeding a coaxial cable run to the shack. Its overall length for 80-10 meters is approximately 102 feet (31 meters) for the flat-top section, with a 34-foot (10.36 meter) matching section. The original design by Louis Varney, G5RV, aimed for efficient operation on 14 MHz (20 meters) as a 3-half-wave antenna, with the matching section providing a good match to 50-ohm coax on that band. While the G5RV offers multi-band capability, its performance varies across bands, often requiring an antenna tuner for optimal SWR on bands other than 20 meters. The matching section's length is critical for its impedance transformation properties, influencing the feedpoint impedance presented to the coaxial cable. Variations like the G5RV Junior and ZS6BKW utilize different flat-top and matching section lengths to optimize performance for specific band sets or to achieve a lower SWR without a tuner on certain bands, demonstrating the adaptability of the basic G5RV concept.

This resource details the computer-optimized design of the _ZS6BKW_ multiband dipole, an evolution of the classic _G5RV_ antenna. It begins by referencing the original 1958 RSGB Bulletin article by Louis Varney G5RV, explaining the operational principles of the G5RV's flat-top and open-wire feedline on 20m and 40m, noting its impedance transformation characteristics for valve amplifiers of that era. The article then transitions to the rationale for optimizing the design for contemporary solid-state transceivers requiring a 50 Ohm match. The core of the project involves using computer modeling to determine optimal lengths for the flat-top and matching section, aiming for a VSWR of less than 2:1 on multiple HF bands. It discusses the process of calculating feedpoint impedance based on antenna length and frequency, referencing professional literature from Professor R.W.P. King at Harvard University. The analysis also considers the characteristic impedance (Z(O)) of the open-wire line, identifying a broad peak of adequate values between 275 and 400 Ohms. Specific design parameters for the improved ZS6BKW are presented, including a shorter flat-top and a longer matching section compared to the original G5RV, with a velocity factor of 0.85 for the 300 Ohm tape. The article confirms acceptable matches on 7, 14, 18, 24, and 28 MHz bands when erected horizontally at 13m, and also discusses performance in an inverted-V configuration, noting frequency shifts. The author, Brian Austin ZS6BKW, emphasizes the antenna's suitability for modern 50 Ohm coaxial cable without a balun.

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