The G5RV Jr. (Half Size) Ham Radio Antenna is a portable, multi-band solution for amateur radio enthusiasts seeking a compact alternative to the traditional full-size G5RV antenna. Originally designed by Louis Varney in 1946, the G5RV Jr. adapts the same principles to a smaller scale, supporting the 10-40 meter bands (28 MHz to 7 MHz). This article provides a step-by-step guide for constructing and installing the antenna based on a user’s documented experience, focusing on the components, tools, and techniques involved in the process.
The G5RV Jr. is particularly well-suited for portable operations and temporary setups, making it a valuable option for hikers, field operators, or those with limited space. The antenna can be constructed using lightweight materials, allowing it to be rolled up and stored in a backpack for on-the-go use with a low-power QRP transmitter.
This guide draws from a detailed build log and offers practical advice on materials, assembly, and tuning considerations. It also highlights the importance of SWR matching and the use of an HF tuner for optimal performance across multiple bands.
Understanding the G5RV Jr. Antenna Design
The G5RV Jr. is a scaled-down version of the original G5RV antenna, which was designed to be a multi-band dipole that could operate on six amateur radio bands without the need for an additional matching system. The Jr. version reduces the size to accommodate four bands—10 meters (28 MHz), 20 meters (14 MHz), 30 meters (10 MHz), and 40 meters (7 MHz)—while maintaining the core principles of the original design.
The antenna is constructed using two 26-foot sections of phosphor bronze stranded wire, which are joined by a ladder line feed system. The use of phosphor bronze offers several advantages: it is highly resistant to stretching, which prevents detuning over time, and it is extremely strong, capable of withstanding significant tension.
To support the antenna, the builder used ceramic egg-style insulators, which are robust and provide good electrical insulation. These insulators also allow for creative mounting solutions, such as inserting ½-inch PVC pipe for additional support. The antenna is intended to be hung at a height of at least 20 feet, ideally on a non-conductive support such as a tree branch.
Components and Materials
The G5RV Jr. requires a combination of conductive materials and insulators to ensure both structural integrity and electrical performance. The following materials are necessary for the construction of the antenna:
- Phosphor bronze stranded wire (26 feet each): Two sections of this wire are used for the main elements of the antenna. The wire is chosen for its strength and resistance to stretching, which helps maintain the antenna's tuning over time.
- Ceramic egg-style insulators: These insulators are used at both ends of the wire elements. They provide electrical isolation and allow for various mounting options.
- Ladder line (window line): This is a 450-ohm impedance line used to connect the antenna to a tuner. A length of 16.5 feet is recommended, with an extra 6–8 inches added to allow for soldering and attachment.
- Coaxial cable (50 ohms): A piece of coaxial cable is needed to connect the tuner to the radio. Recommended types include RG-8, RG-8X, or RG-58U, depending on the power output and desired signal loss.
- RF connectors: These are necessary to connect the coaxial cable to the tuner and the radio. Common connector types include PL259, N-type, or BNC.
The choice of materials can affect the portability and durability of the antenna. For instance, the use of smaller stranded wire or TV twin lead can significantly reduce the weight and allow the antenna to be packed into a backpack for field operations.
Assembly and Construction
The assembly of the G5RV Jr. involves several precise steps to ensure both mechanical stability and electrical performance. Below is a detailed breakdown of the construction process:
Cutting the Wire Elements: Begin by cutting two 26-foot lengths of phosphor bronze stranded wire. These will form the main radiating elements of the dipole. Allow for extra length at both ends to accommodate the insulators and solder connections.
Attaching Insulators: Attach ceramic egg-style insulators to both ends of each wire element. This ensures electrical isolation and provides a secure point for hanging the antenna. The insulators should be positioned so that the wire is centered and balanced.
Preparing the Ladder Line: Cut a 16.5-foot length of 450-ohm ladder line. Add an extra 6–8 inches to each end to allow for soldering. The ladder line will serve as the feed line between the antenna and the tuner.
Connecting the Wire Elements to the Ladder Line: Solder one end of the ladder line to the two wire elements at their center point. This creates the feed point of the dipole. Ensure the connections are secure and well-insulated.
Mounting and Support: Use 550 Para cord to hang the insulators from a suitable support, such as a tree branch or PVC pipe. The antenna should be positioned at least 20 feet above the ground to maximize performance.
Connecting the Coaxial Cable: Connect a 50-ohm coaxial cable to the other end of the ladder line. Use an HF tuner between the coaxial cable and the radio to match the impedance and achieve a good SWR on all bands.
Final Testing: Once the antenna is assembled and mounted, use an SWR meter to check the standing wave ratio across the intended bands. Adjust the length of the coaxial cable if necessary to achieve the best match.
Tuning and Optimization
The G5RV Jr. is designed to work with an HF tuner, which allows for impedance matching across multiple bands. This is a critical aspect of the antenna's performance, as the ladder line feed system has a higher impedance than the 50-ohm coaxial cable used in most modern transceivers.
When using the G5RV Jr., it is important to note that the exact length of the coaxial cable can affect the SWR. Some sources suggest that the coaxial cable can be any length, but this is a disputed point. In practice, it may be necessary to experiment with different lengths to achieve the best match on each band.
An HF tuner can help overcome these challenges by adjusting the impedance to match the antenna's feed point. This allows the antenna to operate efficiently across a wide range of frequencies without the need for additional matching systems.
Portability and Field Use
One of the key advantages of the G5RV Jr. is its portability. The use of lightweight materials and a compact design makes it ideal for field operations, hiking trips, or emergency communications. The antenna can be rolled up and stored in a backpack, making it easy to transport and deploy in various environments.
For portable use, it is recommended to use a low-power QRP transmitter, which is well-suited for the G5RV Jr. The combination of a lightweight antenna and a small transmitter allows for efficient and discreet operation in the field.
When setting up the antenna in the field, it is important to choose a location with minimal obstructions and good elevation. This helps to maximize the antenna's performance and reduce signal loss. The use of a simple support system, such as a tree branch or PVC pipe, can help keep the antenna at an optimal height.
Maintenance and Longevity
The G5RV Jr. is built to last, thanks to the use of durable materials such as phosphor bronze wire and ceramic insulators. These components are resistant to corrosion and wear, ensuring the antenna remains functional for many years with minimal maintenance.
However, it is important to inspect the antenna periodically for signs of damage or wear. This includes checking the wire elements for stretching or breaks, the insulators for cracks or electrical leakage, and the connections for corrosion or loosening.
If the antenna is used in harsh conditions or exposed to extreme weather, it may be necessary to reinforce the support structure or apply protective coatings to the wire elements. Regular maintenance ensures the antenna continues to perform reliably over time.
Conclusion
The G5RV Jr. is a versatile and portable multi-band antenna that offers excellent performance for amateur radio operators. Its compact design and use of durable materials make it ideal for both fixed and portable operations. By following the detailed construction and installation steps outlined in this guide, users can build a functional and reliable antenna that supports the 10-40 meter bands.
The use of an HF tuner is essential for achieving a good SWR match across all bands, and careful selection of materials can enhance the antenna’s performance and longevity. Whether used for emergency communications, field operations, or casual ham radio activity, the G5RV Jr. is a valuable addition to any amateur radio setup.