A Loop on Ground, or simply LOG antenna, is a type of horizontal loop antenna installed directly on or very close to the ground. Unlike traditional antennas that are elevated to maximize their reception and transmission capabilities, the LOG is designed for excellent reception while being practically invisible and easy to install. This innovative approach to antenna design has gained popularity among amateur radio enthusiasts and professionals alike due to its unique advantages.
Benefits of a LOG Antenna
Signal-to-Noise Ratio and Performance
One of the standout features of a LoG antenna is its exceptional signal-to-noise (S/N) ratio. This is especially beneficial in environments with significant electromagnetic interference, such as urban areas. The proximity to the ground helps to attenuate unwanted noise, allowing for clearer reception of HF signals. Additionally, LOG antennas perform reliably in various weather conditions, maintaining stable reception regardless of environmental changes.
Space Efficiency and Pattern Shape Trade-offs
The compact design of a LOG antenna makes it highly space-efficient. A typical Loop On Ground can be as small as 15 feet per side, which is ideal for operators with limited space. While this small footprint might suggest a compromise in performance, the LOG's pattern shape is optimized for effective reception. The antenna’s low elevation pattern allows it to capture signals from a broad range of arrival angles, making it versatile for different operating conditions.
Comparison with Beverage Antennas
Beverage antennas are well-known for their excellent reception capabilities, particularly over long distances. However, they require significant space and grounding to function effectively. The Loop antenna, on the other hand, does not require grounding, which simplifies installation and maintenance. It offers comparable performance in a much smaller area, making it a more practical choice for many operators.
Stealth and Unobtrusive Installation Benefits
For those living in areas with strict regulations or aesthetic concerns regarding antenna installations, the LOG Antenna is an ideal solution. Its ground-level placement makes it virtually invisible, avoiding the need for large, conspicuous structures. This unobtrusive nature allows it to be used in residential areas without drawing unwanted attention, preserving the visual appeal of the surroundings.
Construction Details
Feedpoint Isolation Transformer and Cable Considerations
The feedpoint isolation transformer is a crucial component of the LOG antenna. It isolates the antenna from the feedline, preserving the integrity of the reception pattern. Typically, a 6.25:1 transformer is used, with the antenna side consisting of five turns of wire and the coaxial side having two turns. The choice of cable is also important; a high-quality, low-loss 75-ohm coaxial cable is recommended to minimize signal degradation over long runs.
Constructing the Loop
To construct the Loop of the antenna, start by selecting high-quality insulated wire suitable for outdoor use, such as PVC-coated or enameled wire. Cut the wire to the desired length, typically forming a square loop with sides around 15 feet long, though the exact dimensions can be adjusted based on available space and target frequency range. Lay the wire flat on the ground, forming a square shape, and ensure that the ends meet at the feedpoint where the isolation transformer will be connected.
Installation Methods
Use landscaping staples to secure the wire to the ground at regular intervals, approximately every 18 to 24 inches, to prevent movement caused by wind, animals, or foot traffic. These staples should be placed over the wire, pressing it firmly into the soil without damaging the insulation. This method not only secures the wire in place but also helps to keep it out of the way of lawnmowers and other garden equipment. Once the wire is securely fastened, connect the ends to the feedpoint transformer, ensuring good electrical contact and insulation from the ground. This simple yet effective construction method allows the antenna to blend seamlessly with its surroundings while providing excellent HF reception.
Grounding and Isolation for Pattern Preservation
Although the LOG itself does not require grounding, grounding the coaxial cable shield at the building entry point is essential for safety and pattern preservation. This grounding method provides lightning and static immunity, similar to that of a Beverage antenna, without compromising the antenna’s performance.
Preamplifiers and Larger Antennas
Necessity of Preamplifiers
For most operations, especially on higher bands, the Loop On Ground antenna does not require a preamplifier. The signal strength is typically sufficient to set the noise floor of modern receivers. However, on lower bands like 160 meters, a preamplifier might be beneficial to enhance weak signals. Operators should evaluate their specific needs and test their setups with and without a preamplifier to determine the best configuration.
Larger Antennas
Expanding the size of the LOG antenna can increase signal strength, particularly on lower frequencies. Larger loops can capture more signal, making them suitable for very low-frequency operations. However, on higher frequencies, the pattern may become less predictable, so it is important to balance size with intended frequency use. For versatile operation across multiple bands, maintaining a loop size that does not exceed one wavelength of the highest intended frequency is advisable.
Final Thoughts
The Loop on Ground antenna is a versatile, efficient, and discreet solution for HF reception. Its excellent signal-to-noise ratio, ease of installation, and minimal space requirements make it an attractive option for both amateur radio enthusiasts and professionals. Whether dealing with space constraints, aesthetic concerns, or harsh weather conditions, the LoG antenna offers reliable performance and flexibility, making it a valuable addition to any HAM shack.