The Folded Beverage antenna is a legendary tool for amateur radio enthusiasts, particularly those chasing weak signals on the low bands. Unlike high-gain vertical or dipole antennas, the Beverage is a traveling-wave antenna that excels at providing a quiet, directional receive path. In this post, we break down the specific configuration shown in the diagram and explain how to build a robust termination load capable of handling 100 watts of transmitter power.
Understanding the Beverage Antenna Layout
The diagram illustrates a non-linear Beverage antenna with a total wire length of 41 meters. While traditional Beverage antennas are long, straight wires, this configuration uses a “zig-zag” or dog-leg path to fit into a smaller footprint. The wire used is standard 18 AWG (1 mm diameter).
The antenna begins at a matching transformer and terminates at a 450-ohm resistor connected to a ground rod. The vertical heights vary from 1.5 meters to 15 meters, creating a unique profile that captures electromagnetic waves as they travel along the wire towards the termination.
The Heart of the System: The 9:1 UNUN
Because the antenna wire typically has an impedance of around 450 to 600 ohms, you cannot connect it directly to a standard 50-ohm or 75-ohm coaxial cable without significant signal loss. This is where the 9:1 UNUN (unbalanced-to-unbalanced) transformer comes in. Refer 9:1 UN-UN Long Wire Transformer for HF Antennas
To build the transformer shown in the green box, you need a high-permeability ferrite toroid (like an FT140-43). You wind a trifilar primary (three wires twisted together) around the core. By connecting these windings in series, you achieve an impedance transformation ratio of 9:1. This effectively steps down the antenna’s high impedance to match the 75-ohm coaxial feedline shown in the diagram, ensuring maximum signal transfer to your receiver.
Building a 100-Watt Termination Load
The termination load is critical because it makes the antenna directional. It absorbs signals coming from the “back” of the wire, preventing them from reflecting toward the receiver. While most Beverage antennas are used only for receiving, building a load that can handle 100 watts adds a layer of safety in case of accidental transmission.
To construct a 450-ohm load for 100 watts, you should avoid using a single large wire-wound resistor. Wire-wound resistors have internal inductance that will ruin the antenna’s performance at high frequencies. Instead, use a “parallel array” of non-inductive carbon film or metal oxide resistors.
You can achieve 450 ohms and 100 watts of power handling by connecting ten 4.5k ohm, 10-watt non-inductive resistors in parallel. Alternatively, you can use two 225-ohm “thick film” power resistors in series, mounted on a substantial aluminum heat sink. Always house the resistor bank in a weatherproof, ventilated box to dissipate heat and protect the components from the elements.
By grounding the termination through a 450-ohm resistor, you ensure that the antenna acts as a “one-way street” for radio waves. The signal enters from the direction of the termination and travels toward the transformer. This design reduces atmospheric noise and interference from other directions, allowing you to hear distant stations that would otherwise be buried in static.
Related Posts
- Full Wave Loop Antenna for VHF UHF FM Radio Bands
- DIY Moxon Rectangle Beam Antenna for 10m, 15m, and 20m Bands
- 20–40–80 Meter Loaded Multiband HF Dipole Antenna
- Morgain Antenna: Dual-Band Dipole that Beats Traps
- How to Build a Reduced Size 40M Antenna – Complete DIY Guide