The notation 12.7-j15.4 means a resistance of 12.7 ohms in series with a reactance of -15.4 ohms. Z stands for impedance.There are many variables and an almost infinite number of permutations of element position, length, and diameter.Each set of build dimensions gives rise to a completely different design.
K6Sti Yagi Optimizer Series With AAbove is a 2M Band OWA Dipole example based on Jims original 80M implementation, and configured in K6STIs AOP (professional version) software. Antenna file (.ANT) using Symbolic Dimensions can be seen here. OWADIPOLE.ANT.txt Raising feed-point impedance is particularly useful in yagi design where mutual coupling and loading effects can drop feed-point impedance to very low values, and then become difficult to match whilst also incurring greater losses. Note that to more accurately simulate the original OWA antenna concept, the 144MHz version requires wires (elements) of only 0.5mm diameter in proportion to the increase in frequency and shorter wavelength. Flanking the Split Dipole (the driven element) there are two shorter parasitic elements spaced some 0.01 from the driven element, without this configuration the resultant polar pattern becomes distorted (not symmetrical). Those familiar with yagi design will see these parasitic elements in the same context as the yagis first director (D1) which enhances gain in the forward direction. From a commercial point of view ease of construction and repeatability were of paramount importance After tryingtesting a Hairpin Match detailed in the ARRL VHFUHF handbook and encountering build problems along with poorinconsistent results, time for something different. It was then that I triedtested the concept of Direct Feed and simple Split Dipole driven element. This idea was just starting to become popular and adopted by others. Hairpins are highly reactive located right on the feed-point and so tiny variations in construction give rise to volatility. Software by Lew is very easy to use and true enough delivered a stable and reliable design. Despite these limitations 2M0818SK has a remarkably flat frequency response. Note the OWA style close spacing between the Split Dipole driven element and D1. However, compare overall performance with modern WA9XX AOWA (lower temperature and better GTa in a noisy residential environment simulation) and you will see the difference. It runs hundreds of times faster than NEC- or MININEC- based antenna-analysis programs. YO models tapered elements, mounting brackets, the boom, matching networks, dual driven elements, and conductor loss. It can model two identical Yagis stacked in the H-plane in free space. YO calculates mutual-impedance interactions for all of these cases. It also can ignore Yagi-to-Yagi interaction and model large rectangular arrays of Yagis. Elevation Angle or Gain FOM YO displays elevation angle for Yagis over ground and gain figure-of-merit for single-Yagi, free-space models. YO defaults to a generalized definition of front-to-back ratio. The notation 12.7-j15.4 means a resistance of 12.7 ohms in series with a reactance of -15.4 ohms. Z stands for impedance.
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