The Fascinating History of the Cubical Quad Antenna

The Fascinating History of the Cubical Quad Antenna

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Introduction

The cubical quad antenna is a unique and intriguing design that has a fascinating origin story. Born out of necessity in the early 1940s, this antenna has become a staple in the ham radio community, offering distinct advantages over traditional Yagi antennas. Let's dive into the captivating history of the cubical quad and explore why it continues to be a popular choice among radio enthusiasts.

The Birth of the Cubical Quad

The story of the cubical quad antenna begins at the radio station HCJB , located high in the mountains of Ecuador. In the early 1940s, HCJB, a Christian radio station, decided to upgrade its transmitter to a powerful 10 kilowatt system. However, this increase in power posed a significant challenge – the station's antenna system was literally melting due to the intense electrical activity.

As the station faced this crisis, a team of engineers, led by Clarence Moore (W9LZX), was assembled to find a solution. After poring over radio books for days, Moore had a "divine inspiration" that would ultimately lead to the birth of the cubical quad.

The Folded Dipole Breakthrough

Clarence Moore's eureka moment came when he turned his attention to the folded dipole. The folded dipole, with its lower Q and complete circuit, had a lower voltage at the extremities compared to a conventional dipole. Recognizing the potential of this design, Moore took the next step and pulled the folded dipole open into a square loop, creating the quad element.

To further enhance the design, Moore added a second square loop as a reflector, tuned slightly lower in frequency. This combination of the driven quad element and the reflector loop became the foundation of the cubical quad antenna.

Testing and Validation

With the new antenna design in place, the HCJB team held their breath as they fed 10,000 watts into the cubical quad. To their delight, the antenna performed flawlessly, with no signs of the dreaded corona discharge that had plagued the previous system. Moreover, the cubical quad appeared to provide similar forward gain to the Yagi, solving the station's pressing issue.

Word of the cubical quad's success quickly spread among the ham radio community, and operators began experimenting with and building their own versions of this innovative antenna. One of the key figures in the early exploration of the cubical quad was William Orr, W6SII, who conducted extensive research and published his findings.

Advantages of the Cubical Quad

The cubical quad offers several distinct advantages over traditional Yagi antennas. Firstly, the quad loop takes up significantly less lateral space, with a turning radius of just 8 feet for a 20-meter quad. Additionally, the lower Q of the loop provides better bandwidth, and the antenna is quieter on receive compared to a dipole.

While the forward gain of a two-element quad is similar to a two-element Yagi, the quad benefits from a slightly higher gain in the driven element, making up for the slightly lower gain from the reflector. The quad also exhibits an impressive front-to-back ratio, often exceeding 20 dB, comparable to a Yagi.

Feeding and Multiband Configurations

Feeding a cubical quad can present some challenges, as the inherent impedance of the loop is higher than the standard 50 ohms. This often requires the use of a matching system or the implementation of a remote antenna switch to select the appropriate band when using a multiband configuration.

Constructing a multiband cubical quad can be a complex endeavor, as the elements of each band can interact with and affect the elements of other bands. Careful tuning and adjustment are necessary to ensure optimal performance across multiple frequencies.

Compact and Versatile

One of the appealing aspects of the cubical quad is its ability to be scaled down in size while maintaining reasonable performance. By incorporating loading coils on the vertical sides of the loop, it is possible to create a 20-meter quad that is the size of a 15-meter quad, making it a more compact and versatile option for those with limited space.

While the cubical quad may not be as streamlined in appearance as a Yagi, its performance and unique characteristics have kept it relevant in the ham radio community. Despite falling out of favor in recent years, there are still manufacturers producing cubical quad antennas, and many radio enthusiasts continue to appreciate the advantages this antenna offers.

Conclusion

The cubical quad antenna is a testament to the ingenuity and problem-solving skills of radio engineers. Born out of necessity, this unique design has endured and evolved, offering ham radio operators an alternative to traditional Yagi antennas. Whether you're a seasoned veteran or a newcomer to the hobby, the cubical quad is a fascinating and captivating piece of radio history that continues to inspire and intrigue the ham radio community.

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