Vertical Polarized Half (1/2) Rhombic Array
- skylarkcolo
- Aug 30, 2023
- 6 min read
Updated: Nov 24
In the year 2021, the K0UO station undertook a significant enhancement to its communication capabilities by installing a vertical polarized 1/2 Rhombic antenna, specifically designed to operate across the 40 to 6 meter frequency bands. This particular antenna configuration is known for its efficiency and effectiveness in both transmitting and receiving signals, making it an excellent choice for amateur radio operators and professionals alike. With a center height of 160 feet, the antenna is strategically positioned to maximize its range and performance, allowing for clearer communication over long distances.
Above the ground plane, the half-rhombic antenna exhibits the radiation patterns of a full-rhombic. antenna while the input impedance is half that of a full-rhombic antenna.
One of the crucial factors influencing the performance of this antenna is its dependence on a high-quality galvanic ground connection to the earth. The Ohmic resistance of the ground rod system plays a vital role in ensuring that the antenna functions optimally. In this installation, a 5400-foot deep oil-well casing has been utilized as the grounding mechanism. This choice is particularly significant because deep oil-well casings are often made from conductive materials that provide an excellent grounding path, which is essential for minimizing the risk of electrical interference and enhancing signal clarity.
This grounding system serves a dual purpose; it not only provides an effective ground for the antenna's operation but also acts as a protective measure against lightning strikes, a common hazard in outdoor antenna installations. The environmental conditions at the K0UO site further contribute to the antenna's performance. The area is characterized by its distinctive red soil, which is notably high in iron content. This particular soil composition is advantageous because iron-rich soils tend to exhibit superior electrical conductivity (EC). High EC is critical for ensuring that the ground system effectively dissipates electrical energy, which can improve the overall efficiency of the antenna. Additionally, the conductive properties of the soil can enhance the antenna's radiation pattern, allowing for better signal propagation and reception. In summary, the installation of the 40-6 meter vertical polarized 1/2 Rhombic antenna at K0UO not only showcases advanced engineering and design but also highlights the importance of environmental factors and grounding techniques in optimizing radio communication systems. The combination of a high center height, a robust grounding system using a deep oil-well casing, and the naturally conductive red soil creates an ideal scenario for effective amateur radio operations, ensuring that the K0UO station remains a reliable and efficient hub for communication.
The antenna spans 10 wavelengths on the 40-meter band (1350 feet) and is positioned at a height of 160 feet. It is constructed from a triple galvanized wire rope cable with a diameter of 1/4 inch, meaning it is not merely steel, but triple coated with galvanization. The galvanized cable consists of zinc and other components with higher conductivity. Most commercial AM broadcast towers are zinc-plated. All the large wire antennas are tensioned to withstand a pull of 2500 lbs.
The vertical polarized 1/2 Rhombic has a wider beam, but less gain than the full Rhombic; however, it only requires one tall support, so just make it longer for more gain!
The directivity is in the plane of the legs. Feeding one end with a 9:1 balun and the other end open produces a bi-directional signal. While terminating the far end produces a unidirectional signal at the terminating end. This high gain antenna is used where low angle of radiation is needed.
This antenna also has some higher angle, which can be an advantage for amateur use, for talking to nearer stations.
When considering the design and application of the vertical polarized 1/2 Rhombic antenna, it is essential to understand its unique characteristics and how they can be leveraged for specific communication needs. The 1/2 Rhombic antenna is particularly noted for its ability to provide a wider beamwidth compared to the full Rhombic configuration. This wider beamwidth allows for a broader coverage area, making it advantageous in situations where signals need to be transmitted or received over a larger spatial region. However, it is important to note that this comes at the cost of gain; the full Rhombic antenna typically exhibits greater gain due to its more focused radiation pattern. Despite this trade-off, the 1/2 Rhombic's design is inherently simpler, requiring only a single tall support structure, which can significantly reduce installation complexity and costs.
To enhance the performance of the 1/2 Rhombic antenna, one can simply increase its length. By extending the antenna, it is possible to achieve higher gain, which is particularly beneficial for long-distance communications. The gain characteristics can be adjusted to suit the user's needs, allowing for flexibility in various operational contexts. The directivity of the antenna is oriented in the plane of the legs, which means that the signal strength is maximized in that direction. When the antenna is fed at one end using a 9:1 balun, it facilitates the creation of a bi-directional signal, allowing for effective communication in both directions along the axis of the antenna. This feature is particularly useful for point-to-point communications where signals need to be sent and received without needing to reposition the antenna.
On the other hand, if the far end of the antenna is terminated, it converts the setup into a unidirectional antenna. This configuration is advantageous when the user wants to focus the signal in a specific direction, effectively eliminating any unwanted reflections or interference from the opposite side. This high-gain antenna is especially valuable in scenarios where a low angle of radiation is essential, such as in long-range communications where signals need to penetrate the ionosphere and reach distant stations. The low angle of radiation helps in achieving better propagation characteristics, which is crucial for effective communication over vast distances.
Additionally, the 1/2 Rhombic antenna does exhibit some higher angle radiation, which can be particularly beneficial for amateur radio operators. This characteristic allows operators to establish reliable communication with nearby stations, facilitating local contacts and enhancing overall communication capabilities. The ability to communicate effectively with both distant and nearby stations makes the 1/2 Rhombic antenna a versatile choice for amateur radio enthusiasts. By understanding the different configurations and optimizing the antenna's length and feed methods, users can tailor their setup to maximize performance based on their specific communication requirements.
The half-rhombic antenna is essentially one side of a rhombic antenna used against the ground. However, because of the lossy soil, it cannot function like a true rhombic antenna due to ground reflections and losses. Despite its name, this antenna operates more like a terminated, end-fed, inverted V, achieving its best performance when the centerpoint is slightly elevated above the ground. In Bruce's 1931 article, it is referred to simply as an inverted-V. The term "half-rhombic" was later coined by other builders. Various adaptations of the rhombic antenna have been developed to meet specific commercial and governmental and DOD communication requirements, resulting in highly complex wire structures that go beyond the scope of these introductory notes. Nonetheless, the variations we have chosen should provide a solid foundation for you to understand the classical literature on advanced rhombic designs.
All long Traveling wave antennas are known for fantastic Improvements in the reduction of QSB fading, for both transmit or receive.
It is like Diversity, theses large arrays cover a lot of area. My station uses over a mile of wire, so you are both listening and transmitting signals coming and going at different angles. Signal-to-noise ratio (S+N/N ratio, or SNR) is one technical aspect not too many amateurs give a second thought about, however if you can't hear them you can't work them. This is very apparent on audio reception,long Traveling wave antennas eliminates much of the audio amplitude fading for both transmit or receive. The RF signal is almost never in a stable phase relationship at both places at the same time. This means the signal will have random phase and amplitude differences. The arrival angle and polarization of incoming signals will change. This generally results in the fading, by having many wavelengths of wire in the air, the chances are that while one experiences a fade, the other will not. The power is in the diversity size of the array and what you can now hear with out QSB fading. Traveling wave antennas are just quieter and have substantial noise reduction. That is why so many people use the Beverage receive antennas.
The K0UO antenna test range site makes use of the 4KS Walz airport and its surrounding area as a practical learning environment for STEM (Scientific, Technical, Engineering, & Mathematics) antenna projects in a real-world outdoor setting. If your group has a university aerospace or antenna research STEM program, please let me know.
TO SEE the complete Blog list check @ https://www.k0uo.com/k0uo
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