For VHF enthusiasts, especially in the 2-meter amateur radio band (~146 MHz), the quest is always for more gain and a lower radiation angle for greater distance. The design in these schematics presents a clever, compact solution Stacked 5/8-wave VHF Antenna: a stacked array of two 5/8-wave vertical elements fed with a unique “bazooka” coaxial balun.
It’s a dual-5/8-wavelength colinear array — basically two 5/8λ radiators stacked vertically with a matching network in between to improve gain and impedance. This design is attributed to Ramón Miranda,YY5RM , and has circulated in the amateur radio community in Spanish/English plans and on QRZ.com profiles.
A colinear array is multiple radiating elements stacked in phase to increase gain and narrow the vertical radiation angle — great for local/medium VHF coverage.
This design have:
- Two 5/8λ elements (L1 and L2) ~122 cm each at ~146 MHz.
- A matching section (B1) ~48 cm of wound turns (coil) between them.
- A 7-turn choke or coil at the feed point, with a tap on the 5th turn for coax feed.
- A ground/radial plate ~49 cm wide at the bottom.
Dimensions shown (e.g., 122 cm and 48 cm) are based on roughly 5/8 of the 2 m wavelength and are adjustable for best SWR.
Stacked 5/8-wave VHF Antenna – Why It’s Unique
This isn’t a standard J-pole or ground plane. It’s a two-element, verticallyStacked 5/8-wave VHF Antenna Here’s what makes it tick:
- The Core Principle: Stacking for Gain. Two 5/8-wave vertical radiators (
L1andL2) are placed one above the other. When fed in-phase, this “stacking” focuses the signal’s energy toward the horizon, providing significant gain over a single element and pushing the signal farther. - The Magic Component: The Bazooka Balun (B1). This is the coil you see between the two elements. It’s not just a phasing coil; it’s a 1:1 coaxial choke balun. Its primary job is to prevent the feedline shield from carrying RF current, which would distort the antenna’s pattern and cause feed line radiation (making your cable part of the antenna).
- Telescopic Tuning. The top element (
L2) is telescopic. This allows for a fine-tuned adjustment of the antenna’s resonant point to achieve the lowest possible SWR (Standing Wave Ratio) at your exact operating frequency.
Understanding the Design
This Stacked 5/8-wave VHF Antennais essentially a 5/8 wavelength radiator that stands approximately 292 cm tall from base to tip. The beauty of this design lies in its extended electrical length, which provides lower takeoff angles and better DX performance compared to a standard quarter-wave ground plane antenna.
The antenna consists of three main sections. At the top, you’ll find the L2 radiating element measuring 122 cm, which acts as a telescopic adjustable section. This adjustability is crucial because it allows you to fine-tune the antenna for minimum SWR. The middle section features the B1 matching coil, which is 48 cm long and contains between 65 to 85 turns of wire. The exact number of turns depends on both the L2 length and the coil diameter you choose. At the bottom, there’s the L1 section, another 122 cm radiating element that connects to your feed line.
Stacked 5/8-wave VHF Antenna –Critical Adjustments
- Maximize Signal First: You adjust the number of turns on the B1 balun coil (between 65 and 85 turns, depending on its length and wire thickness) while monitoring an RF field strength meter. You add or remove turns until the radiated signal is at its absolute maximum. This ensures the elements are correctly phased.
- Minimize SWR: Only after step one do you adjust the section (L2) to fine-tune the electrical length and achieve the lowest SWR. This sequence is crucial for optimal performance.
The Ground Plane System
At the base of the antenna, you’ll notice a ground plane system consisting of 7 radial elements. These radials are approximately 49 cm long and should be positioned at a downward angle. There’s also a tap point on the 5th turn of a 7-turn loading coil at the base, which helps with impedance transformation and provides a connection point for your coaxial feed line.
The radials don’t just provide a ground reference; they also contribute to the antenna’s radiation pattern by helping to establish the proper current distribution along the radiator. The slight downward droop helps to lower the feed point impedance closer to the 50-ohm characteristic impedance of standard coaxial cable.
Practical Construction Tips
When building this antenna, wire gauge and coil form diameter for B1 will affect the number of turns needed. Larger diameter coils generally require fewer turns, while smaller diameters need more. Start somewhere in the middle of the 65-85 turn range and adjust from there based on your measurements.
The 65 cm spacing shown between the top of your equipment (the SWR meter or RFS meter in the diagram) and the start of L2 is important for keeping the feedline away from the radiating element to minimize interaction.
Using telescopic tubing for L2 makes adjustment much easier during the tuning process. You can gradually extend or retract this section while monitoring your SWR meter until you find the sweet spot where SWR is minimized.
Performance Characteristics
The 5/8 wavelength design offers several advantages over shorter antennas. The radiation pattern is compressed vertically, concentrating more energy toward the horizon rather than straight up. This makes it ideal for distance communications on VHF frequencies. You can expect approximately 3dB gain over a standard quarter-wave ground plane, which translates to roughly doubling your effective radiated power.
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